AFTES Recommendations · Split Set® Swellex® Nominal diameter (mm) 31 to 80 28 to 37 28 to 37 20...

Rock Bolting Technology

GT6R4A1

www.aftes.asso.fr

FRENCH TUNNELLING AND UNDERGROUND SPACE ASSOCIATION

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32 M TUNNELS ET ESPACE SOUTERRAIN - n°241 - Janvier/Février 2014

RECOMMENDATION OF AFTES N°GT6R4A1

Rock Bolting Technology

Table of contents

1 - Introduction: bolting definition and typology- 3-1.1 - End-anchored bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

1.2 - Distributed anchor bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

1.3 - Mixed bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

1.4 - Friction bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

1.5 - Sliding and other types of bolts . . . . . . . . . . . . . . . . . . . . . . .9

1.6 - Face bolting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

1.7 - Raft bolting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

2 - Drilling 11-2.1 - Drilling techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

2.2 - Drilling works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

2.3 - Special works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

3 - Bolts 19-3.1 - The rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

3.2 - Tip or anchorage device . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

3.3 - The head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

3.4 - Distribution plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

3.5 - Corrosion protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

3.6 - Useful dimensioning characteristics . . . . . . . . . . . . . . . . . . .23

4 - Anchorages 24-4.1 - End-anchorage or mechanical anchorage . . . . . . . . . . . . . . .24

4.2 - Resin or grout bedding . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

4.3 - Hydraulically expandable friction bolts . . . . . . . . . . . . . . . . .32

4.4 - Driven friction bolts (forced) . . . . . . . . . . . . . . . . . . . . . . . . .33

4.5 - Mixed anchorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

4.6 - Self-drilling bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

5 - Safety during the bolting phase 38-5.1 - Reference texts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

5.2 - Risk evaluation and analysis . . . . . . . . . . . . . . . . . . . . . . . . .39

5.3 - Measures to be envisaged . . . . . . . . . . . . . . . . . . . . . . . . . . .40

6 - Bolting inspection 41-6.1 - Inspection principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

6.2 - Inspection of constituent parts . . . . . . . . . . . . . . . . . . . . . . .42

6.3 - Operational methods for tensile and bolt pull-out tests . . . .43

6.4 - Supervision of bolts during site works . . . . . . . . . . . . . . . . .48

7 - Interpretation matrix 49-

AFTES welcomes all suggestions relating to this text.

Text presented by Paul ROUX (Spie batignolles TPCI) Leader of Working Group 6

With the collaboration of:Patrick BIENFAIT (Egis Tunnels) - Stéphane BLOND (Bec Fayat) - Anne BOUVARD (Tractebel Engineering) - Guy CUEILLE (Retired) - Sylvain ECKERT (Vicat)

Michèle FEMELAND (CETU) - Romain GARNERO (Spie batignolles TPCI) - Daniel GILLE (Atlas Copco) - Christophe JASSIONNESSE (GEOS)Philippe KOENIG (Atlas Copco) - François LAIGLE (EDF/CIH) - Bernard LASNE (Consultant) - Renzo MARUCCO (Mecsider)

Patrick SABY (Metal Service/Thema) - Rémy WITTMANN (Minova)

This recommendation has been approved by the AFTES Technical Committee following a critical review of the text by:Pierre HINGANT (EGIS) - Alain MERCUSOT (CETU) - Jean PIRAUD (ANTEA) - Loïc THEVENOT (EIFFAGE) - Jean LAUNAY (VINCI) - Christian PLINE (GEODATA)

32_49recoGT6 uk_Mise en page 1 18/02/2014 13:04 Page32

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33

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TUNNELS ET ESPACE SOUTERRAIN - n°241 - Janvier/Février 2014


Bolting technology, the subject of this recommendation, represents one of the

most fundamental elements participating in tunnel support techniques using

conventional methods.

The recommendation concerns (Fig. 1):

• radial bolting, vault, side walls, raft

• face bolting (longitudinal)

• bolting by oblique longitudinal threading

Bolting may be completed by other means of support: arches, shotcrete,

mesh…

It is limited to works using standard materials. Specific technologies calling

on particular equipments such as very long bolts (over 15 m, cables or ties)

are not considered.

The length of radial bolts is generally between 1/3 and 1/2 of the greatest

excavation opening. Consequently and insofar as standard works are concer-

ned, their length does not exceed 6 m. For longitudinal bolting, the length of

the bolts is generally between 8 and 15 m.

Generally speaking, there are five main types of bolts:

1.1 - End-anchored bolts

End-anchored bolting consists in linking the plan area of the excavated surface

to a deep intact rock point. The anchoring is generally carried out using a

mechanical system (Fig. 2) but can occasionally be associated with the fixing

of the bar at the base of the hole using resin.

Generally, anchoring at the base of the hole is obtained by blocking an expan-

sion shell on the face of the hole following the driving in of a wedge using the

mechanical traction obtained by screwing. The tensioning of the bolt by pres-

tressing – by tightening the head nut or by expansion or decompression of the

ground – is essential to obtain optimal efficiency for this support system.

The major advantage of end-anchored bolting is its rapid installation and imme-

diate efficiency. However, this efficiency is only maintained over time if the

rock does not creep near the anchorage point.

In addition, this type of bolt can be installed in the case of water seepage in

the borehole.

The standard characteristics are 16 to 20 mm diameters for lengths of between

1.50 and 3.00 m.

1.2 - Distributed anchor bolts

Distributed anchor bolting consists in sealing metal (or other) bars over their

entire length in the anchorage hole. The sealing product is generally resin,

cement mortar or grout (Fig. 3).

The sealing distributed over the entire length of the anchorage hole ensures

the bolt’s long service life.

1.2.1 - Resin sealing

The resin is generally introduced into the anchorage hole in the form of

cartridges.

This type of sealing is generally used for bolts up to 4 m in length. Efficiency

is generally obtained in 5 to 15 minutes.

1 - Introduction: bolting definition and typology-

Screwing to the plate

groove wedges

Fig. 2 - Diagram showing the

end-anchored bolt.

Screwing in the groove

nut

bar

single bearing plate

Fig. 3 - Distributed anchor bolt diagram.

Radial bolting Longitudinal face bolting

Forepoling

Fig. 1 - Diagram showing the various types of bolting used.


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RECOMMENDATION OF AFTES N°GT6R4A1 M

1.2.2 - Mortar sealing

This sealing consists in driving the bolt into the anchorage hole which has first

been filled with a thixotropic mortar. This allows the mortar to be held in posi-

tion, even in vertical holes bored into the roof, as well as an excellent filling of

the borehole.

This type of sealing is generally used for bolts less than 5 m long. Its efficiency

depends on the time it takes for the mortar to set.

1.2.3 - Grout sealing

This sealing consists in injecting the bolt with grout once it has been positioned

in the borehole through the intermediary of a tube or a flexible pipe attached

to the rod.

This type of sealing is generally used for bolts longer than 5m. Its efficiency


1.2.4 - Particular case of self-drilling bolts (Fig. 4)

These types of bolts consist of a hollow metal rod with, at its end, a lost drill

used to bore out the anchorage hole. The sealing is carried out by injecting the

sealing product through the interior of the bolt.

The self-drilling bolt is particularly well-adapted to fractured ground and long

anchorage lengths.

Its efficiency depends on the time it takes for the sealing product to set (cement

grout, mortar or resin).

This type of bolt is also used for threading.

1.3 - Mixed bolts

The mixed bolt is one that is

locally anchored and, in a

second stage, sealed by

injecting a sealing product.

These bolts present the

advantage of providing

immediate efficiency thanks

to their local anchorage and

their capacity to subse-

quently be injected, thus

improving their service life

and performance levels.

Certain friction bolts can be equipped with a lost drill which is used for drilling

(self-drilling) and become mixed by injection (Fig. 6).

1.4 - Friction bolts

Friction bolts are thin, hollowed metal profiles in close contact with the rock

over their entire length. This allows them to be held in place by friction. They

are immediately efficient.

The friction between the ground and the bolt can be provided in two different

ways:

• Either by hydraulic expansion of the profile in the borehole, using pressurised

water injection within the closed tube profile (Fig. 7).

Nut Flat plateCoupler with centre stop enabling direct end-to-end bearing between rods thereby minimizing energy loss during drilling

Fig. 4 - Diagram of a self-drilling bolt, type MINOVA SDA®.

The anchor rod made of high-qualitytubes with continuous cold-rolled drillthread (standard left-hand rope or trapezoidal thread)

Domed platemade of cold-formed flat steel

Protection tube if required Grout

Various drill bits enablequick drilling of boreholes

in diverse soil and rockconditions

Injection hoses and vent

Mechanical anchoragesystem

Steel rod

Bolting drill hole filledwith grout or mortar

Fig. 5 - Schematic diagram of the mixed bolt.

Fig. 6 - Diagram of a self-drilling friction bolt.

1. Friction bolt2. Anchor plate3. Drill bit

4. Drilling rod5. Strike ring6. Sleeve

Steel expansion tube

Bearing plate

Fig. 7 - Diagram of a Swellex® type bolt.


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• Or by forced pushing of a split tube in the borehole, with the initial diameter

of the split profile being greater than that of the hole (Fig. 8).

The friction bolt works by rubbing against the hole walls. In the case of the

Split Set®, the possibility of injecting and bedding the profile increases the

anchor’s capacity.

1.5 - Sliding and other types of bolts

There exist sliding bolts adapted to the brutal rock burst conditions.

These can be mixed type bolts

such as “Cone Bolt®”: The forces

produced by the brutal deforma-

tion of the rock are transferred to

the rod via the anchor plate. For

these forces to attain the opera-

tional distributed anchorage limit,

a special rod coating allows for

greater sliding.

The sliding of the rod in the bedding results in the punching of the grout by

the anchor and permits a bolt movement that retains its efficiency (Fig.10).

Other systems aiming to absorb brutal rock deformations have been developed

using, for example, the deployment of angled elements forming several

segments of the “D-Bolt®” rod (Fig.11).

1.6 - Face bolting

This technique is used to anticipate a deformation of the working face. The

bolts are positioned perpendicular to the face.

The resumption of tunnelling in the bolted face requires the use of easily

destructible bolts. These are generally in fibreglass and sealed over their entire

length using cement grout.

For geotechnical and site reasons, these are generally very long bolts: 1.5 to

2 times the diameter of the excavation. As the works progress, the bolts are

installed in such a manner as to maintain an overlap over approximately a

third of their length.

1.7 - Raft bolting

In certain cases, rafts can receive reinforcement provided by radial type bolting,

metal bolts or fibreglass bolts for excavations carried out in several phases in

swelling ground.

Fig. 8 - Diagram of a Split Set® type bolt.

Fig. 9 - Diagram of the Cone Bolt® type mixed bolt.

Fig. 10 - Diagram showing the operation of the "cone bolt®".(based on McKenzie, R, Use of Cone Bolts in Ground Prone to Rockburst, Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2002).

Fig. 11 - Diagram of the D-Bolt® type bolt.

Before rockburst After rockburst

2 - Drilling-

Type of bedding LocalFriction

Resin MortarSplit Set® Swellex®

Nominal diameter (mm) 31 to 80 28 to 37 28 to 37 20 to 32 20 to 32

Drilling diameter (mm) 32 to 89 33 to 46 32 to 45 28 to 41 38 to 64

In accordance with the manufacturer’s recommendations, the recommended drilling diameters are as follows:


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For bolts bedded in mortar, the drilling diameter depends on the quality of the

ground and the length of the bedding. It varies between 1.5 to 2 times the rod

diameter.

For bolts bedded in resin, it is necessary to pay attention to the drilling per-

formance to respect the optimum cover for the bolt rods.

2.1 - Drilling techniques

In “normal drillability” ground, being one that can be drilled without excessive

wedging or loss of fluids, and within which the holes can be left open for the

time needed to install bolts without any deterioration, the main drilling methods

are as follows (Fig. 15 and Fig. 16):

2.1.1 - Rotary percussion drilling (rotation fracturing)

Rotary percussion drilling (Fig. 12) is generally carried out using “jumbos”

equipped with hydraulic drills. The tool is a bar with a drill bit screwed onto

the end.

A manual method using pneumatic hammers allows small diameter holes with

a limited length to be drilled.

2.1.2 - Rotary drilling (with scaling)

The rotary drilling boring rigs (Fig. 13) do not have a striking system. The drill

bit generally has two tungsten carbide or polycrystalline diamond inserts.

This method, reserved for certain types of ground, is highly productive and

permits relatively small drilling diameters.

2.1.3 - Other drilling methods

2.1.3.1 - Rotary – rotative drilling by grinding (Fig. 14)This drilling method, which uses a tricone bit as a tool, is for large diameters

holes not used for bolting.

2.1.3.2 - Down-the-hole hammer drillingThis type of drilling, not much used for bolting, is reserved for large hole dia-

meters. This type of hammer transmits the percussion energy straight through

to the drill bit without the intermediary of rods. These are compressed air ham-

mers and have standard dimensions ranging from 80 to 500 mm.

Fig. 14 - Rotarydrilling bit.

Free surface

Crushed zone

Fractured zone

Movement direction Impact force

Rock

Fig. 12 - Rotary percussion drilling.

Drill bit

Movement direction

Cutting of a slice by shear force

Rock

Fig. 13 - Rotary drilling. Fig. 16 - Eimco-Secoma Nomagram no.2.

AFTE

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AFTES DU hardness rating

Rota

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drill

ing

area

AVER

AGE/

STRO

NG T

HRUS

T

Rotative drilling

areaSTRONGTHRUST

Rotative drilling areaAVERAGE THRUST

Drilling areaSTRIKING

Fig. 15 - Eimco-Secoma Nomagram no.1.

AFTE

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unia

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RC

com

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Drilling diameter in mm

Rotation

Rotary

down-the-holehammerHammer outside

hole

Bolting area

Two-lipped PCDdrill bit

Two-lipped tungstencarbide drill bit


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2.1.4 - Summary: indicative data applicable to bolting

2.1.5 - Tools

Drilling tools comprise drill bits, rods and connection accessories (couplings,

fittings, etc.).

For standard bolting, the holes to be made have small diameters (less than

50 mm) and lengths of no more than 4 to 6 m. As from 6 m, the bars shall be

coupled and have much larger drilling diameters.

2.2 - Drilling works

2.2.1 - Removal of cuttings

To remove cuttings in tunnels, drilling using water injection is preferred over

foam or compressed air.

The hole is cleared either by cleaning out and/or blow-out using compressed

air when the bar is removed. Cleaning is necessary for all ground reinforcement

systems. However, it is necessary that cleaning be carried out very carefully

in the case of sealed bolting and, in particular, resin sealings.

2.2.2 - Drilling machines for bolting

Expressed simply, the installation of a bolt requires three stages:

• The drilling of a bolt hole

• The installation of the bolt

• The tightening and/or sealing

There are several possible ways to mechanise the installation of the bolts and

several levels of mechanisation.

It is possible to use the same “jumbo” for drilling both blast holes and bolting

holes (Fig. 17). These “jumbos” can be equipped with telescopic guides to

adapt the drilling lengths to the blasting and bolting boreholes. The equipment

can be provided with articulations to ensure that the (radial) bolt can be posi-

tioned with perfectly adapted kinetics.

However, the current trend is towards drilling further with parallel blast holes

and using jumbos with two or three arms. However, the kinetics of the arms

permitting deeper drilling then becomes incompatible with the radial drilling

of bolt holes. To that end, specific machines are now available, either with

mechanical drilling and manual positioning, or that completely automate the

process for positioning the bolts.

There are therefore machines equipped both with an arm provided with a

drilling guide for blasting and a cradle arm from which the operators install

the bolts.

There are also rock bolting rigs that fully mechanise the installation operation.

These are equipped with a guide on which is positioned the drilling tools, a

bolt rack and the mechanism for installing the bolts. The magazine is generally

limited to 10-12 bolts (Fig. 18). The size of the plates that can be positioned

in the rack is limited. There are also racks and installation systems suitable

to several types of bolts.

Currently, automated rock bolting rigs are used for:

• Local mechanical anchor bolts

• Distributed anchor bolts, resin sealed

• Split Set® type friction bolts

• Swellex® type friction bolts

For mechanical anchor bolts and resin sealed distributed anchor bolts, the bol-

ting turret is equipped with a rotative device to tighten the bolt or turn the rod

in the resin. Certain automated bolting rigs permit the simultaneous placing

of a mesh.

For Split Set® type friction bolts, the rotative device is replaced by a hammer.

For Swellex® type friction bolts, it is replaced by an insert and an end fitting

permitting the injection of water into the bolt.

Depending on the machinery and type of ground, it is now possible to econo-

mically drill boreholes with diameters ranging from 32 to 89 mm for standard

lengths of 4 to 8 m with a potential bar lengthening operation. It is therefore

in this “range” of boreholes that bolting should preferably be used. The choice

Fig. 17 - : Mixed drilling / bolting arm.

Fig. 18 - Bolting turret.

Drilling methodStandard min.

diameterStandard max.

diameterCommentaries

Rotary percussion drilling (drill bits) 32 mm 89 mm Ø max = 127 mm

Rotary percussion drilling(monobloc borer) 28 mm 34 mm

Ø min = 24 mmLength limited to 3 m


Possibility of 15 m longholes


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of the type of bolt to be installed helps in specifying the type of drilling to be

envisaged, especially in terms of diameters.

Given the overall dimensions, especially of the rock-hammer and hoses, it

is important that the length of bolts that can be installed in a gallery of a

given size be determined during the design phase. Depending on the equip-

ments used, the length of the boom is equal to the length of the bolts plus

1 to 2 m.

2.3 - Special works

In ground that is “difficult to drill", it is necessary to either envisage drilling

with pipe driving, or to use bolts from the self-drilling range.

It is also possible to envisage using a grout type borehole fluid during drilling.

For these special applications, non-standard machines specially equipped for

these works are used.

3 - Bolts-

3.2 - Tip or anchorage device

This term designates the end of the bolt at the end of the borehole.

Its function varies according to the types of bolts considered:

• Straight cut for bolts sealed by injection.

• Tip or bevelled cut for cartridge sealed bolts: it permits the piercing of the

resin or mortar cartridges and favours a good mix.

• Truncated cone end with reduction of diameter to simplify the introduction

of friction bolts.

• Equipped with a drill bit, it permits the hole to be drilled for self-drilling

bolts: the various versions of the drill bits can be treated or equipped with

carbide inserts or teeth in the form of a cross, an arch, etc.

• Equipped with a shell, it provides local anchorage for the bolt: these ancho-

rages are formed from a central plug into which, depending on the contact

surface being sought on the borehole wall, between 2 and 6 leaves are

inserted. They are constructed from steel or an aluminium alloy. Traction

exerted on the rod causes the shell to expand. The choice of type of shell

must be adapted to the geological conditions encountered and be validated

by tests (see § 6).

3.3 - The head

This term designates the projecting end of the bolt that permits the inter-

locking of the distribution plate and the bolt.

In most cases of local anchor bolts or distributed sealing bolts, it has a thread

of between 100 and 200 mm receiving a hexagonal coupling nut. These

threads can be trimmed but are generally rolled. The type of threading can

have an influence on the bolt capacity.

There can also be specific versions:

• Forged hexagonal heads to allow the rotational drive of resin sealed HA rods

or to reduce the projecting part of local bolts. In this case, the bolt is tightened

by rotating the rod in the anchorage head.

• Threaded ends completed by a rotational drive device for the HA rods, such

as flats and driving squares, resined or forged feed nuts, rivet or pinned

nuts.

In the case of self-drilling or threaded profile steel bolts, or in the case of glass

This chapter is devoted to the properties of the bolt, including its accessories

and particularities (thread, flanges, head, and bearing plate).

The following must be defined for each type of bolt:

• The materials used for the rod and its accessories

• The mechanical characteristics of the rod and its accessories (see §3.1)

• The geometrical characteristics of the rod and its accessories

The main materials used are steel alloys, fibreglass or, exceptionally, carbon

fibre. The choice of materials used must be adapted to the sought-after per-

formances (elastic limit, elongation at rupture, destructibility, etc.).

3.1 - The rod

This is the central part of the bolt. Depending on the type of bolt, it either has

a solid or hollow section.

The rod can be smooth in the case of friction bolts and local anchor bolts or

ribbed in the case of distributed sealing bolts. In the latter case, the flanges

improve the mixing of the sealing resin and thus the sealing itself.

It is also worth mentioning the bolt whose flanges provide a continuous thread

and permit the length to be adjusted on site (GEWI® type bolt).

In the case of self-drilling bolts, the rod can potentially be formed from several

elements connected by a threaded sleeve.

The standard thread profiles are:

“chord” type (the most common) “T” type

The “chord” type thread provides a good seal around the sleeves. The “T” type

thread makes unscrewing easier.

Non-standard thread profiles are also used.

In the case of bolts made from composite materials, all types of sections can

be used.


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fibre bolts with threaded profiles, the bolt heads are simply equipped with

a nut.

Friction bolts either have a ring or a welded end fitting that bears on the

anchorage plate installed prior to prior to driving the bolt.

3.4 - Distribution plate

The bearing plates (Fig. 19) represent an important support element and can

be used independently or in association with mesh, straps or brackets. They

provide a containment of the rock mass at the head of the bolt.

It is also possible to use metal sheeting to increase the bearing surface of

these plates.

There are three main types of plates:

• Rigid plates dimensioned in such a way as to provide static bearing points

when compared with the bolts with which they are associated.

• Flexible or self-compensating plates permitting gradual deformations in

function of the loads on the bolts.

• Special plates for injection, doubling up to hold the mesh, and reinforce-

ment (“spider” type).

through the intermediary of the head, with tightening of the nut using an impact

wrench or, where required, a torque wrench. The tightening torque must be

adapted to the type of bolt and nut.

The dished plate permits a certain adaptation to deformation.

An auxiliary plate, clipped or screwed to the threaded bolt head, is generally

used to attach the reinforcement mesh or nets when this type of system is

used in addition to the bolting.

The use of the bolter and a storage turret calls for the use of plates with

dimensions adapted to the equipment (≤15x15cm). This can be unfavourable

for the mobilisation of the ground cone at the top of the bolt and the connection

with the facing.

For glass fibre bolts, the plate can be held by a wedge inserted into the head

of the bolt separating the blades or the two parts of the bolt. However, this

procedure does not provide optimal tightening. There are also cylindrical glass

fibre bolts with threading on the head that permit the fixing of a plate through

the use of a nut. In general, the head of the glass fibre bolt represents a low

resistance area.

3.5 - Corrosion protection

When the operational duration of the support makes it necessary, corrosion

protection can be provided:

• Continuous mortar, grout or resin sealing

• Excessive thickness of the parts

• Hot dipped galvanisation of the parts

• Epoxy protection (hot painted)

• Coating by cold bituminous dipping

• Injected sheathed bolts (Fig. 27)

• Stainless steel bolts

3.6 - Useful dimensioning characteristics

In agreement with the recommendations of the AFTES (GT 30) work group on

“the design and dimensioning of radial rock", the main mechanical characte-

ristics useful for the dimensioning of bolting, and dependent on the types of

bolts and manufacturer references, are as follows:

• The resistance of the rod in traction at the yield strength, in kN

• The resistance of the head (plate fixing system) in traction at the elastic limit,

in kN

• The resistance of the rod at breaking strength, in kN

• The resistance of the head (plate fixing device) at breaking limit, in kN

• Relative elongation of the rod in traction at the yield strength, in %

• Relative elongation of the rod at breaking strength, in %.

These characteristics, obtained by laboratory traction tests on all or part of the

elements forming the bolt on completion of the manufacturing process, must

be guaranteed (“minimum guaranteed value”) and are independent from

installation conditions (drilling, sealing, etc.).

Rigid plates Adjustable jointed plates

Fig. 19 - Examples of plates.

Distribution plate for injected bedding

Injection Évent

Spider plates

The bearing plates usually have 15 to 20 cm sides and are 4 to 10 mm thick.

They are either flat, dished or jointed with a circular or oblong hole. This permits

a better adaptation to the effective angle of the bar and nut borehole.

For friction bolts, the plate is immediately operational without tightening.

For local or distributed anchor bolts, the plate is tightened against the facing


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The rod characteristics can theoretically be ascertained from the geometrical

characteristics of the bolt and the mechanical characteristics of its parts, such

as:

• The resistant section of the rod, in m²

• The elastic limit stress at the traction strength of the material, in MPa

• The elastic deformation module (Young module) of the material, in MPa

• The maximum tensile stress of the material, in MPa

• The deformation at maximum tensile stress, in %

These characteristics are theoretically accessible with a HA B500B bolt, (HA

= High Adherence, B = Bar, 500 = elastic limit in MPa, B = ductility rating)

but need to be adapted for more specific bolts such as friction bolts and mixed

bolts. This is why it is always better to privilege the knowledge of characte-

ristics that can be directly measured on the bolt.

Bolting in a rock mass also implies the mobilisation of the shearing charac-

teristics of the bolts, in other words under the action-effect of relative move-

ment transversal to the rod axis. This would seem to be a complex operation

involving the combined characteristics of shearing and the traction of the bolt

itself, as well as those of the rock and, where applicable, the sealing

product.

No standardised test exists to characterise this operation but a number of

experimental or theoretical approaches are underway.

4.1 - End-anchorage or mechanical anchorage

The anchorage of the bolt is carried out using a shell that generally comprises

2 to 6 leaves and a central plug. A threaded rod is inserted into the groove (Fig.

20 and Fig. 21).

The shell branches are spread during the tightening of the bolt. The shell

wedges are positioned up against the hole walls and the rod is prestressed.

The bolt is installed by tightening the coupling nut located on the plate to a

torque recommended by the manufacturer.

The choice of the type of anchorage depends on the nature of the rock and

should be decided in accordance with the results of preliminary tests.

The anchorage depends on the following parameters:

• The quality of the rock around the anchorage point (min. compressive

strength): below a compressive strength of 10 MPa, it is necessary to use

special shells. In this case, local anchor bolting is not recommended

•The shell surface in contact with the ground: it progresses in inverse propor-

tion to the ground strength

• The materials forming the shell

• The respective diameters of the shell and the drilling hole

• The initial tightening of the nut

The main advantage of local anchorage is to produce an immediate contain-

ment after installation and thus immediate safety. Its installation is simple and

fast.

During installation, the adequate tightening of the bolt should be checked

alongside making sure that the plate is in very close contact with the ground.

Time and/or vibration caused by blasting can result in scaling around the plate.

The efficiency of the bolt is reduced to zero if the plate is no longer in contact

with the ground.

Where possible, it is worthwhile checking and retightening the plate at least

once.

4.2 - Resin or grout sealing


Resin permits the sealing of the bolt over its entire length. This type of sealing

4 - Anchorages-

PlugShell

rod

Fig. 20 - Operating principle for mechanical anchorage.

Two branches Six branchesThree branches

Fig. 21 - Examples of expansion shell.


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is only adapted to rock permitting a good anchorage hole calibration. There

are “fast” and “slow” resin setting times.

The resin is generally provided in the form of cartridges containing a catalyser

and a hardener (Fig. 22).

Currently, given the materials available and the high viscosity of the resins,

the mechanical installation of the sealed bolts can be carried out over a length

of up to 5 m. This limit is imposed on the resistance of the resin during mixing.

The resin hardening time, and thus the sealing, is generally between 5 and 15

min (depending on the product and the temperature) and provides this type of

bolt with extremely rapid efficiency. This is a vital choice factor for the type of

bolting used.

The important parameters for installing the resin bolt are:

The diameter of the bolt hole and its good performance over the entire length

The annular space between the hole and the chosen rod (Fig. 23).

• The cleaning of the hole which must have had all borehole residues (cuttings)

removed

• The depth of the hole: excessive depth will result in an increased consump-

tion of resin and inefficient mixing

• The resin loads must be introduced and pushed to the rear of the hole and

the position of the loads in the hole must be checked. A parachute can be

used to retain the resin loads in the hole while awaiting the introduction of

the rod

• The installation of the bolt must comply with the supplier’s recommendations.

The various stages in the procedure are as follows (Fig. 24) :

- The introduction of the rod, turning it while pushing it towards the rear

of the hole

- Mixing: maintain the rotation of the rod once it has reached the rear of

the hole to permit a good mix between the resin and the hardener

- Tightening once the resin has set

Using an automated rock bolting rig, the introduction of the cartridges in the

hole is generally carried out using a compressed air “blowpipe”. This requires

a hole that is clean and free from any elements that might damage or prevent

the installation of the cartridges. This is often the most delicate aspect of the

installation sequence.

The following parameters must be checked:

• The mixing time which depends on the type of resin: insufficient time will

not allow the resin to harden in a proper manner, but an excessive mixing

time will impair the polymerisation of the resin and consequently the satis-

factory anchorage of the bolt.

• The rotation speed which needs to be checked and the mixing time must be

adapted to the envisaged speed.

• The installation temperature influences the resin setting time.

The storage of the resin cartridges must be taken into consideration when set-

ting up and managing the work site:

• Storage life is short: maximum of a few months at an average temperature

of 20-25°C. This storage period reduces if this average temperature is not

maintained. It is recommended that the stock be rotated.

• The storage temperature must not fall below 0°C.

• The cartridges should preferably be stored in a cool, dry environment pro-

tected from direct sunlight.

• During installation procedures, if the storage temperature is too different

from the installation temperature, it will be necessary to leave sufficient time

for the resin temperature to attain that of the installation temperature.

• The elimination of residues and waste must use adapted channels.

The resin cartridges are delivered in boxes containing 20 units. The packaging

shall bear at least the following information:

• Supplier / Origin

• Type of product and contents of individual cartridges

• Pictograms and, where applicable, safety notices

• Date of manufacture

• Expiry date

• Lot number

For certain applications, the resin

can be injected by pumping.

Catalyser

Resin

Fig. 22 - Resin cartridge.

Diameter of drill hole D

Annular space e

Diameter of rodd

Fig. 23 - Annular space between the hole and the rod.

Fig. 24 - Stages for the installation of a resin bolt.


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4.2.2 - Mortar or grout sealing

This sealing product takes the form of mortar cartridges, dry mortar in sacks

or pumpable grout.

The mortar used (cartridge or sack) incorporates a high resistance, rapid set-

ting cement. For the grout, the sand used must be fine to be pumpable. Unless

expansive, its shrinkage must be limited.

The cement, additives and water based grout is generally more liquid and its

installation more complicated than the mortar-based operation. It can be pre-

pared on site

Parameters to be checked for grout or mortar specifications:

• The setting times must be adapted to the required work

• The product thixotropy must permit pumping

• The product must be of the limited shrinkage type and even be slightly

expansive

• The steel corrosion protection must not be attacked by the product

• Mechanical compression and bending

4.2.2.1 - Pumped anchorage mortarsPumped mortars are mixes specifically prepared for the work site or dry pre-

mixed, ready-to-use and prepared by the formulators.

The ready-to-use mortars have had additives added and generally have cha-

racteristics that make their installation easier and improve the quality of the

anchorage: thixotropy, lack of shrinkage, pumpability. They can provide rapid

hardening, allowing the bolts to be tensioned after 4 or 5 h depending on the

objectives being sought. At 24 h and depending on the product, strengths can

attain between 15 and 35 MPa.

Standard installation procedure:

a) Preparation of the mortar:

- Mixing of the mortar in compliance with the manufacturer’s recom-

mendations, especially insofar as the quantity of water is concerned

- Mixing

b) Mortar injection using a pump, filling from the base of the hole towards

the head:

- An injection hose is introduced to the rear of the hole

- The mortar injected by the pump pushes the hose towards the exterior.

There must be a certain resistance to the rising of the hose to ensure

the filling of voids and gaps

c) Introduction of rods simply by pushing:

- The introduction of the bolt permits the distribution of a certain quantity

of mortar in any gaps in the ground

- At the end of the operation, the mortar should normally come out at

the head of the bolt via the annular space between the rod and the

hole

- A wooden wedge is occasionally used to maintain the bolt in the hole

during the setting of the sealing (for sub-vertical bolts)

d) Tighten the bolts once the mortar has set: the mortar setting time depends

on the characteristics of the chosen product and the installation tempera-

ture.

Injection after the installation of the bolts can also be envisaged.

The parameters influencing the installation of the sealing products are:

• The time between the mixing and the installation (max. 15 to 20 mn), which

depends on the ambient temperature and the temperature of the mixing

water

• The time between the injection and the installation of the bolt bar

• The ambient installation temperature and the rock temperature. Installation

is not recommended if the temperature is too low (below 5°C)

• The water dosage

4.2.2.2 - Composition of site mortarsFor basic mortars prepared on side, the weight batched dose is as follows:

• 1 cement

• 1 sand (0-3 mm or less)

• 0.3-0.35 (water/cement)

It is possible to obtain mortars presenting considerable early strength by

using rapid setting hydraulic binders (Vicalpes® type) or quick-setting

cement.

Example of a one hour quick-setting mortar composition:

• Sand 0-2mm: 55%

• Filler: 11%

• Vicalpes® R 17%

• CEM I 52.5 R 17%

• Water

• Additives

This mortar has a strength of 6 MPa at 3h and 18 MPa at 24h.

4.2.2.3 - Anchorage mortars in cartridgesThe cartridges contain a ready-to-use dry mortar packaged in permeable

packing permitting water absorption. Their use is limited to small quantities

of bolting works and for short bolts. The cartridges are positioned by tamping

(rammer). The bolts are then introduced by being simply pushed in.

4.3 - Hydraulically expandable friction bolts

These bolts are steel folded in on themselves. They are introduced into the

hole and then inflated using high pressure water.

The expansion pressure for the installation is around 30 MPa. It is necessary

to check its compatibility with the quality of the rock. In all cases, it is essential

Type of mortarSetting time

(à 20°C)Rc 2 h Rc 1 day Rc 1 day

Fast 28 - 30 min 5 -10 MPa 20 - 35 MPa 35 - 70 MPa

Standard 1 - 2 h 25 - 40 MPa 35 - 70 MPa

Slow 4 - 8 h 25 - 40 MPa 35 - 70 MPa


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that it be defined and described in the site bolting procedures (preliminary tests).

The high pressure inflation pumps must be inspected and revision works car-

ried out on a regular basis.

Bolt installation procedure (Fig. 25):

• Drilling of the hole

• Insertion of the bolt in the hole, connection to the inflation hose

• Inflation, between 30 s and 1 min

• End of installation

Parameters influencing the anchorage:

• Quality of steel used: there are two main qualities of Swellex® type bolts

(standard range and manganese range)

• Corrosion resistance: it is possible to obtain bolts with an anti-corrosion finish

• Quality of the tube manufacturing process and the end welds

• Water injection pressure

• Quality of the rock in the ground: this type of bolt is adapted to a ground

whose resistance is compatible with the inflation pressure. For other types

of ground, sleeves are used to avoid damaging the ground near the head of

the hole

The drilling diameter is checked for each type of bolt and in compliance with

the manufacturer’s recommendations

4.4 - Driven friction bolts (forced)

These friction bolts take the form of a steel tube with a high elastic limit, slotted

along its full length.

Characteristics of the friction bolt:

• Easy installation (by percussion hammer)

• Active and dynamic friction reinforcement system. The bolt controls the

expansion of the ground thanks to its considerable elongation and failure-

free shearing

• Corrosion resistance: hot-dipped galvanised bolts can be obtained

• Currently, its length is limited to around 4 m

Installation procedure (Fig.26):


• Insertion of the bolt equipped with its plate in the hole

• The hammer is positioned and the bolt thrust into the hole. The thrust must

be maintained until contact is made between the plate and the facing

Parameters to ensure the satisfactory positioning of the friction bolts:

• The drilling diameter must be checked and the supplier’s recommendations

respected

• Ground characteristics: this type of bolt reveals its efficiency in fractured

ground where it can maintain the position of the blocks

• The quality of the water in the massif influences the durability of the bolt

The installation of the bolt is relatively simple, and this represents its main

advantage.

4.5 - Mixed anchorage

There are several mixed anchorage bolt combinations. Generally speaking,

the aim is to obtain the advantages of an immediate anchorage guaranteed

by an expansion shell, and the long-term resistance of a distributed anchorage

bolt.

While this is often a combination of local and distributed anchorages, other

combinations exist, such as:

• End-anchored bolt + injection of resin or cement between the hole and the bolt

• Friction + injection of cement in the bolt tube

4.5.1 - End-anchored bolt + cement Injection

It is possible to simultaneously obtain the advantages of a mechanical ancho-

rage and a distributed anchorage by using mechanical anchor bolts with a

subsequent injection of a resin or cement grout into the bolt hole.

Fig. 25 - Installation of a expandable rock bolt.

© A

tlas C

opco

Fig. 26 - Installation by thrusting of a friction bolt.

© M

etal S

ervic

e

Drilling- 35 à 38 mm (SS39)- 41 à 46 mm (SS46)

Installation

Bolt installed- Radial forces- Considerable

plate pressure


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Certain types of bolts have a hollow rod into which the sealing product can

be injected (as per self-drilling bolts) between the bar, the local anchorage

and the ground. Other bolts (CT Bolts®) permit the injection of the sealing

product between a PVC casing and the bolt rod up to the head of the ancho-

rage (Fig. 27).

4.5.2 - Friction + cement injection or filling

The thrust friction bolt (§ 4.4) can be injected with a mortar or grout after ins-

tallation.

There is also a percussion type of thrust driven friction bolt that can receive

cartridges containing a slightly expansive cement-based binder (Fig. 28).

When setting, the cement produces a pressure on the tube forming the bolt

and reinforces its keying in the ground, thus increasing the force needed to

slide the anchorage (10 to 15t/m).

Fig. 28 :- Example of a mixed anchorage (friction + cement injection), injected Split Set® type.

4.6 - Self-drilling bolts

4.6.1 - Steel bolts

Self-drilling bolts are formed from hollowed rods, equipped at their base with

a lost drill. Having drilled with the fluid returning through the annular gap, grout

is then injected via the rod providing the bolt sealing.

These systems directly replace the drilling bar and the drill bit. They are des-

igned to be positioned alongside standard rotary percussion machinery.

As the anchorage is of the distributed type, the factors influencing the quality

of the anchorage will be the same, although with certain additional difficulties:

the diameter of the drill bit must be sufficiently small to allow the annular

space to have a good mortar or grout sealing. However, it must also be suffi-

ciently large to permit the good evacuation of the cuttings.

Water, air or grout drilling is possible.

Although not widely used, it is possible to envisage a sealing

using a pumpable sealing.


• Drilling of the hole using the bolt rod

• Potential adding of a length through the use of a sleeve

• Injection

• Installation of the plate

4.6.2 - Glass fibre bolts

Glass fibre self-drilling bolts are available. Their main advantages are:

• They are injectable

• They are not heavy

• They do not suffer from corrosion

• They are easily destructible and therefore well adapted for temporary

supports in areas that will subsequently be excavated.

They are installed in the same way as the rotary drilling method.

4.6.3 - Self-drilling friction bolts

This type of bolt operates in the same way as the pipe driving method, but in

this case, the pipe is split, similarly to the rammed Split Set® type friction bolt.

The hammer, used for the drilling, also pushes the pipe into the hole, resulting

in a friction anchorage immediately after its installation (Fig. 30).

Fig. 27 - Example of the installation of a mixed anchorage bolt, CT Bolt® type.

Fig. 29 - Installation of a self-drilling bolt.

Fig. 30 - Procedure for the installation of a self-drillingfriction bolt (DSI®).

Power Set drill bit

AT - Pc

Power Setdrill

Power Set adapter

© A

tlas

Copc

o


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Once a type of bolting is chosen, the contractor needs to respect a certain

number of conditions to ensure that the installation of the bolting elements

takes place as safely as possible.

The bolting takes place after the purging of the walls and the face, or after the

application of a first layer of containment shotcrete.

5.1 - Reference texts

The "Guide des bonnes pratiques pour la Sécurité et la protection de la Santé

lors de travaux sousterrains" (guide to good safety and health protection prac-

tices when carrying out underground works) published by CARSAT-RA is a

reference document used by the client, the project manager and the contractor

to draw up engineering and site works documents relative to safety (SPS,

SSHPP, Procedures, etc).

Reminder of the logic to be respected for the implementation of the PGP (gene-

ral prevention principles) such as defined in article L 4121-2 of the French

Labour Code:

• Avoid professional and environmental risks

• As far as possible, evaluate unavoidable risks

• Privilege inherent protections by using operational methods adapted to the

workplace, using adequate equipment and materials and always take care

to respect the following rule which consists in adapting the work to the labour

force and not the other way round

• Always privilege collective protection systems and, where needed, install

adapted individual protection systems

• Provide personnel with training concerning the risks they are liable to encounter.

5.2 - Risk evaluation and analysis

Bolted support works present various types of risks. They can stem from a wide

range of sources, from the supply of materials and equipment through to the

installation of the support, without forgetting the “inspections” phase. They essen-

tially result from the installation of supports and the monitoring of their behaviour.

Risks linked to the ground must be taken into consideration as excavations

that have not yet been provided with supports present serious dangers, espe-

cially rock falls.

The analysis of the “bolting” activity begins as from the supply of the materials

and equipment. It is a phase during which the workers carry out repetitive

handling tasks that can occasionally call for physical efforts that can lead to

bad posture. The locations of materials and equipment delivery and return

areas shall be organised in such a way that these movements do not cause

any traffic accidents.

The drilling phase can be the source of several risks, some of which linked

to the materials and equipment. They can concern:

• Hand or fingers getting caught while, for instance, installing a rod or chan-

ging drill bits

• Impulsive impacts resulting from vibrations produced by jackhammers

The lack of lighting as well as excessive lighting in work areas can result in risk

situations. During drilling, the noise and dust from an insufficiently equipped drilling

machine can be a source of discomfort and occupational diseases for workers.

The bolt installation phase presents risks that are common to all types of

bolts as well as other risks specific to the types of bolts used. The handling

of the bolt and its introduction in the drilling hole can result in injuries to

hands and impacts resulting from the use of sledgehammers. Concerning

vault bolts, working on a cradle can be the cause of various tools and ins-

truments falling onto lower areas.

The installation of distributed bedded anchor bolts presents risk linked to

the use of injection pumps. The preparation of sealing products can lead to

risks of skin burns, inhalation and even ingestion of dust (fines). During the

injection phase, the breakage of a hose can take place, leading to the same

risks discussed for the preparation phase.

During the installation of local anchor bolts, the risks are essentially linked

to the handling of accessories and the positioning of the anchorage shells,

plates and tightening nuts.

For friction anchorages, the risks depend on the types of bolts. Bolts whose

efficiency is only effective once they have absorbed water, alongside bolts

rammed into the ground, present risks linked to the installation materials

and equipment; with water injection pump for the former and striking system

machinery for the second.

5.3 - Measures to be envisaged

The measures to be envisaged for monitoring the behaviour of the bolts,

whether during the excavation phase or during the working life of the struc-

ture where the supports remain surface mounted, call for inspections.

The stakeholders involved in the construction (specifier, client, project mana-

ger, health, protection and safety coordinator and contractors), as well as

infrastructure managers shall refer to paragraph 6.4 of the present recom-

mendation – “Surveillance des boulons” (bolt monitoring) during the works.

The measures to be envisaged insofar as risks linked to the ground are

concerned are:

• Ground monitoring: assignment of a person responsible for inspecting the

supports

• Systematic preliminary purge, privileging the use of mechanical purging.

The measures to be envisaged with regard to risks linked to materials and

equipment during drilling are:

• Set up training courses covering the use and maintenance of drilling

machinery

5 - Safety during the bolting phase-


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• Ensure that cradles meet the needs of safety regulations and their specific

uses.

• As far as possible, mechanise jobs (when the section and number bolts to

be installed make it possible): delivery of bolts, changing the borehole rods

and bars

• If drilling is carried out manually, provide for supports on which to place

materials and equipment (tripod) and lay out the work space at the base

of the wall to be bolted to avoid any risk of employees falling

• Prevent other employees from approaching: to guard against the risk of

personnel becoming involved in collisions or entanglements next to the

drilling machine should there be a sudden movement of the guide, it is

necessary to define a safety perimeter around the machines as well as

certain safety rules to attract the attention of the operator when someone

enters his working vicinity.

• Avoid generating dust and any projection of materials: privilege water or

air/water mix drilling. In granular ground or ground whose nature presents

health risks, install a dust collection system and ventilation in the work

area.

• Concerning noise: privilege electrohydraulic and soundproofed machinery

and equipment, but without reducing the requirements of wearing indivi-

dual protection gear.

The measures to be envisaged concerning the risks linked to the installation

of the bolt are:

• Privilege the use of bolting robots.

• If the bolting is to be carried out manually, provide training adapted to the

various types of bolts.

• Wear adapted individual protection gear.

6.1 - Testing principles

To ensure bolting quality and efficiency, several types of inspections and

tests can be carried out at various stages.

There are:

• preliminary tests carried out at the project stage to validate the envisaged

bolting system and, in particular, its dimensioning given the quality of the

ground to be bolted (tests that can go as far as pulling out the test bolt)

• suitability tests prior to the works, to check the adaptation of the chosen

bolting system with the installation procedure and the in situ conditions,

especially those concerning the ground

• on arrival on site, a systematic inspection of the various constituent parts

(bolts and sealings) as well as an inspection of the installation machinery

and materials

• inspection tests carried out during works on anchorages forming part of

the support system, to check their efficiency

It is also possible to examine the bolts over time by permanently fixing dyna-

mometric units at the head of the anchorage between the plate and the nut

and to occasionally note the deformation using a comparator.

These inspections and tests are further detailed in the following paragraphs.

6.2 - Inspection of constituent parts

The quality of the various constituent bolting parts (bolts, expansion shells,

self-drilling drill bits and other accessories) and the installation machinery

and equipment shall be inspected:

• During the approval procedure, by checking the laboratory tests carried

out by the supplier (yield load, ultimate load, elongation at failure, especially

for the rods, etc.). The supplier’s inspection reports must be checked on

delivery to the site.

• On delivery and installation: diameter, length, thread, head and tip,

absence of rust, grease, etc.:

- For HA rods whose diameters are set by AFNOR standards (14 - 16

- 20 - 25 - 32 - 40) and thus subject to an approval certificate, it is

essential that the supply be accompanied by a valid description

sheet concerning the NF AFCAB of the supplied steel,

- For HA rods whose diameters are not covered by AFNOR standards

(18 - 22 - 26 - 28 - 30 - 34, etc.), it is essential that the supply be

accompanied by a certificate from the producing steel mill; this docu-

ment shall indicate the data identifying the product (casting number,

chemical analysis, etc.) as well as the yield load values (Re, act), the

tensile strength values (Rm) and their relative “relations”, and finally,

the total elongation (Agt) expressed as a percentage. All this shall be

in compliance with the NF A 85-080-1 (2010-10) standards.

For the friction bolts, it is necessary to inspect the markings specific

to each bolt allowing its traceability, in accordance with the concer-

ned standard,

- All these values determine the mechanical characteristics of the

steel.

• The quality of water and sand used for the mortars,

• The storage conditions for the various constituents.

Concerning the sealing products (resin, grout, mortar), the following shall

be checked:

• For the resins: condition of the cartridges on delivery, expiry date

(generally several months, storage conditions, polymerisation speeds,

etc.

• For the grouts and mortars: compressive strength at 7 d and 28 d, vis-

cosity, setting times: six test samples at the injection lance outlet for

each shift,

• For mortars in cartridges: condition of the cartridges on delivery,

storage conditions.

6 - Rock bolting testing-


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It is necessary to cover oneself against the risk of counterfeits:

• Traceability

• Marking

• Standardisation system

• Compliance certificate

In addition, it is necessary to ensure that the quality control covers all the

bolt manufacturing stages and that the test bolts are the same as those that

are installed.

6.3 - Operational methods for bolt tensile and pull-out tests

Concerning inspection tests for mortar sealed bolts:

The test result will depend on the setting of the sealing grout as well as on

the convergence and “tightening” of the bolt following an increase in the

ortho radial stress.

The test should therefore be carried out when there is a low convergence

speed:

• under low cover: 3 mm/day

• under strong constraint: 1-2 cm/day

6.3.1 General principles concerning bolt tests

The tensile and pull-out tests carried out on the bolts generally use a hollow

cylinder that allows the bolt head to be pulled by resting against the rock

wall around the anchorage bearing plate (Fig. 31).

For the mechanical anchor bolts, tests can be carried out with the torque

wrench used to place them in tension.

The movement of the bolt head is measured using a comparator. This makes

it possible to trace the load-movement curve characterising the behaviour

of the bolt and its anchorage.

Tensioning is carried out in stages. At each stage, the changing displacement

or tension loss if applicable, defines a tensile creep resistance (or slipping)

of the anchorage. It is therefore possible to define a peak resistance and, in

certain cases, a residual resistance.

The preliminary tests and suitability tests are to be carried out on specific

anchorages that do not form part of the structure support system or that do

not participate in the stability of the operational structure.

For open-air supports, the preliminary tests and suitability tests are generally

destructive in order to measure the resistance of the sealing necessary for

the dimensioning of the support. However, preliminary tests and suitability

tests are not necessary underground. They are carried out in the same way

as the inspection tests and in the same bolt and ground conditions as those

for the structure where they will be used. (see below).

However, in certain cases, the Engineer can ask for destructive tests in order

to evaluate the Tu (in kN) resistance of the anchorage in the ground. This is

generally in function of the anchorage length (or qs expressed in kPa which

is the conventionally agreed lateral friction).

The number of tests to be carried out per type of anchorage and by type of

geological conditions is to be set in the contract specifications. The average

strength is often defined on the basis of a minimum of five tests per type of

anchorage and by type of geological conditions. This is because a fairly wide

dispersion is generally observed.

The preliminary tests and suitability tests result in a test report.

The inspection tests are to be carried out on anchorages forming part of the

structure support system. An inspection is carried out to ensure that the

anchorage resists a test tensile strength defined during the design phase

and which is in function of the bolt’s tensile strength service limit (generally

test tensile strength = tensile strength service limit or rather 1.2 x tensile

strength service limit).

For an anchorage with immediate efficiency, testing should be carried out

rapidly after its installation.

For mortar or resin sealed bolts, testing must be carried out as soon as the

setting of the sealing allows it (7 to 28 days for the mortar, 8 to 24 hours for

the resin, in accordance with information provide by the supplier and in

accordance with contract requirements).

Deferred testing can also be carried out to check the service life of an ancho-

rage (see § 6.4).

6.3.2 - Standards and recommendations

For anchorages bedded into the rock (mortar or resin), the pull test procedure

as well as the testing procedure is described by the XP P 94-444 (December

2002) standard – Static pull test under an axial traction load for an anchorage

sealed in a rock mass – Staged tests:

• The bolts are tensioned by incremental loads and/or movements and mea-

sures are taken at each increment once the load and movement have been

stabilised (noting the stabilisation period). The stages are set at 5 minutes.

• The breaking strength test comprises two loading/unloading cycles per

stage, with the 1st cycle up to the estimated stress limit and the 2nd cycle

up to twice this stress. The test provides the Tu limit traction force asso-

ciated with the length L of the reinforcement bedded into the rocky mate-

rial.

• The inspection test (Fig. 32) is carried out over a single load cycle subdi-

Fig. 31 - Tensile test system.


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vided into five 5 minute stages until Te is obtained followed by an unloading

over three 1 minute stages (see figure 2). It might also be necessary to

maintain the last Te stage over a longer period (20 or 30 minutes) prior

to carrying out the inspected unloading. The test is deemed conclusive if

the average resistance of the tests is greater than either Ts or 1.1 times

Ts (in accordance with contract requirements).

The ISRM recommendation and the ASTM standard use similar methodologies.

They are described up to the pulling out of the anchor. Their references are as

follows:

• ISRM – Suggested Method for Rockbolt Testing (1975),

• ASTM D 4435-84 (reapproved 1998) – Standard Test Method for Rock Anchor

Pull Test.

In the case of breaking strength tests, measures must be taken to:

a) Avoid breaking the reinforcement under the effect of maximum traction:

- by choosing a sufficient section

- and/or limiting the length of the sealing; however, the latter must be

sufficient to absorb all unevenness in the ground

b) Limiting the edge effects:

- either by providing a minimum free length when bolt sealing (around

1 m in the ground and 0.5 m in the rock)

A check of the non-sealed length of the anchorages is carried out by introducing

a rod in the annular space free from any sealing.

- or by having test equipment positioned on the ground around the rock

bolt head, but where all points of the bearing surface are at least 0.3 m

from the edges of the hole

c) for bolts sealed into the rock (using mortar or resin), the test shall take place

after a minimum setting time (7 to 28 days for the mortar, or 8 to 24 hours

for the resin, in accordance with information provided by the supplier and

contract requirements)

The pull tests on the friction bolts are carried out in the same way. They take

place immediately after installation (refer to manufacturer’s instructions). Tests

on several bolt lengths (minimum of three) provide a more reliable evaluation

of the qs limit friction value. The qs value can increase under the effect of

ground movements around the excavation.

Apart from bolts in tunnels, being the subject of the present recommendation,

there are other test procedures concerning micropiles and nails or ancho-

rages in loose ground. This results in adding the concept of creep to that of

tensile strength, alongside anchorage ties. These tests are generally intended

to determine the qs limit side friction value necessary for the dimensioning

of the concerned structures (stability of studded slopes, foundations, etc.)

but can also concern underground structures:

• Large structures

• Works requiring strict deformation inspections

• Proximity of existing structures

• Clayey rock

• Etc.

These procedures are mentioned here as a reminder:

• CLOUTERRE 1991 recommendations

• Controlled movement tensile tests (constant speed)

• Controlled load tensile tests (creep stages)

• NF P 94-242-1 (1993) standard – Static nail pull test subject to an axial

traction load – Constant movement speed test

• ISRM - Suggested Method for Rock Anchorage Testing (1985)

• NF P 94-153 (1993) standard – Static anchorage tie test

• Chapter 6 of TA 95 recommendations

• NF EN 1537 – Anchorage tie works: several test methods proposed in § 9

and appendix E

6.4 - Surveillance of bolts during site works

During the excavation phase, at a distance to the rear of the face determined

according to the vibrations caused by blasting or under the effect of ancho-

rage sliding, it is necessary to check that the nuts are well tightened and,

where required, to carry out a systematic retightening of all the local anchor

bolts. This type of inspection is also recommended prior to the application

of the last few layers of shotcrete or prior to the installation, depending on

the case, of membrane or a concrete lining.

Bolts with broken or breakable heads must be changed or replaced by ano-

ther support system.

As a reminder, it is possible to monitor the tension of a bolt by placing either

a dynamometric packer or a loading cell between the bolt head and the rock.

An overall inspection of the support system represented by the bolting, whether

or not associated with shotcrete, is carried out. It particularly includes conver-

gence methods within the framework of the “interactive design” method, for-

merly know as the “observational method”. Should a behaviour be judged

abnormal, it may be necessary to reinforce the bolting system (increased den-

sity, diameter and/or length of bolts, reduction in the time taken for installation

in relation to drilling progress on the face, choice of another type of bolt, etc.)

or completely modify the support system (such as heavy arches).

Fig. 32 - inspection test. Loading – unloading programme (in accordance with XP P 94-444).

T Traction forceTe Traction force imposed for the inspectiont Time in minutesP Test preparation phase


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If when tensioning a local anchorage bolt or if, after a certain time span,

there is a rock scaling or break-up and that there is no longer any contact

between the anchorage plate and the ground, then the bolt becomes ineffi-

cient and must be replaced.

In structures where the support remains surface-mounted, it is necessary,

to ensure the long service life of the support. To that end, the contractor, up

to the handover of the structure, or the client over the entire working life of

the structure, must perform periodic inspection measures and carry out the

required actions.

Water circulation, flow above all when particularly aggressive, can result in

the steel rusting. This reduces the efficiency of the bolt and its anchorage. In

this case, it is recommended that corrosion protection products are used, or

to use distributed anchor bolts, or seal local anchor bolts over their entire length

once tensioned, and to protect the plate and nut. However, these precautions

in no way replace the need to carry out periodic inspections.

7 - Interpretation matrix-

BOLTS

DATA

Occasionallocal anchorbolts bolts

Distributed anchorage bolts Mixed bolts(occasional

anchorage +sealing)

Hybrid boltsfriction

anchorage +sealing)

"Cone Bolt®" * type bolts

Self-drilling bolts Friction bolts

Glass fiberbolts

Carbon bolts

Mortar sealing

Resin sealing

Type "MinovaSDA®"

"Alwag" type ATPower®

Type "Swellex®"

Type "Split Set®"

Traction +++ ++++ ++++ ++++ +++ ++ +++ ++ +++ +++ ++ ++

Shear + ++++ +++ +++ ++ ++++ +++ ++ ++ +++ ++ ++

Fractured ground ++ ++ + ++ +++ +++ ++++ +++ ++ ++ ++ ++

Mediocre grounddrillability

o + + o o + ++++ ++++ + o + +

Permanent character

+ ++++ +++ ++++ +++ ++++ +++ o ++ ++ + ++

Immediate action ++++ o +++ ++++ ++++ +++ ++ ++++ ++++ ++++ +++ +++

Delayed action ++ +++ ++++ +++ +++ ++++ ++ +++ +++ +++ +++

Nuisance caused bythe presence of

water++++ + +++ R ++ ++ ++ + ++++ ++++ +++ ++ R ++ R

Water drainage ++++ ++ + ++ + ++ ++ +++ ++ ++++ ++ ++

Waterproofing o ++ +++ R ++ ++ ++ ++ o + + ++ ++

Installation time ++++ ++ +++ +++ ++ +++ +++ ++++ ++++ +++ +++

Legend

++++ Recommended

+++ Good

++ Average

+ Acceptable

o Not recommended

To be checked

Traction: Ability to retain or carry: also depends on the bolt's mechanical characteristics

Shear: Resistance to side movements: also depends on the bolt's mechanical characteristics

Fractured ground: Ground with low RQD: risk of jamming

Action: Immediate or delayed action

Water: Drilling flow

Need for waterproofing or drainage

R: Aqua-reactive resin t

* "Sliding" bolt that, after a slide, retains its efficiency

This table is provided to simplify the choice of bolts. It does not include the cost of supplies or accessories.


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Bolting technology, the subject of this recommendation, represents one of the

most fundamental elements participating in tunnel support techniques using

conventional methods.

The recommendation concerns (Fig. 1):

• radial bolting, vault, side walls, raft

• face bolting (longitudinal)

• bolting by oblique longitudinal threading

Bolting may be completed by other means of support: arches, shotcrete,

mesh…

It is limited to works using standard materials. Specific technologies calling

on particular equipments such as very long bolts (over 15 m, cables or ties)

are not considered.

The length of radial bolts is generally between 1/3 and 1/2 of the greatest

excavation opening. Consequently and insofar as standard works are concer-

ned, their length does not exceed 6 m. For longitudinal bolting, the length of

the bolts is generally between 8 and 15 m.

Generally speaking, there are five main types of bolts:

1.1 - End-anchored bolts

End-anchored bolting consists in linking the plan area of the excavated surface

to a deep intact rock point. The anchoring is generally carried out using a

mechanical system (Fig. 2) but can occasionally be associated with the fixing

of the bar at the base of the hole using resin.

Generally, anchoring at the base of the hole is obtained by blocking an expan-

sion shell on the face of the hole following the driving in of a wedge using the

mechanical traction obtained by screwing. The tensioning of the bolt by pres-

tressing – by tightening the head nut or by expansion or decompression of the

ground – is essential to obtain optimal efficiency for this support system.

The major advantage of end-anchored bolting is its rapid installation and imme-

diate efficiency. However, this efficiency is only maintained over time if the

rock does not creep near the anchorage point.

In addition, this type of bolt can be installed in the case of water seepage in

the borehole.

The standard characteristics are 16 to 20 mm diameters for lengths of between

1.50 and 3.00 m.

1.2 - Distributed anchor bolts

Distributed anchor bolting consists in sealing metal (or other) bars over their

entire length in the anchorage hole. The sealing product is generally resin,

cement mortar or grout (Fig. 3).

The sealing distributed over the entire length of the anchorage hole ensures

the bolt’s long service life.


The resin is generally introduced into the anchorage hole in the form of

cartridges.

This type of sealing is generally used for bolts up to 4 m in length. Efficiency

is generally obtained in 5 to 15 minutes.

1 - Introduction: bolting definition and typology-

Screwing to the plate

groove wedges

Fig. 2 - Diagram showing the

end-anchored bolt.

Screwing in the groove

nut

bar

single bearing plate

Fig. 3 - Distributed anchor bolt diagram.

Radial bolting Longitudinal face bolting

Forepoling

Fig. 1 - Diagram showing the various types of bolting used.


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1.2.2 - Mortar sealing

This sealing consists in driving the bolt into the anchorage hole which has first

been filled with a thixotropic mortar. This allows the mortar to be held in posi-

tion, even in vertical holes bored into the roof, as well as an excellent filling of

the borehole.

This type of sealing is generally used for bolts less than 5 m long. Its efficiency


1.2.3 - Grout sealing

This sealing consists in injecting the bolt with grout once it has been positioned

in the borehole through the intermediary of a tube or a flexible pipe attached

to the rod.

This type of sealing is generally used for bolts longer than 5m. Its efficiency


1.2.4 - Particular case of self-drilling bolts (Fig. 4)

These types of bolts consist of a hollow metal rod with, at its end, a lost drill

used to bore out the anchorage hole. The sealing is carried out by injecting the

sealing product through the interior of the bolt.

The self-drilling bolt is particularly well-adapted to fractured ground and long

anchorage lengths.

Its efficiency depends on the time it takes for the sealing product to set (cement

grout, mortar or resin).

This type of bolt is also used for threading.

1.3 - Mixed bolts

The mixed bolt is one that is

locally anchored and, in a

second stage, sealed by

injecting a sealing product.

These bolts present the

advantage of providing

immediate efficiency thanks

to their local anchorage and

their capacity to subse-

quently be injected, thus

improving their service life

and performance levels.

Certain friction bolts can be equipped with a lost drill which is used for drilling

(self-drilling) and become mixed by injection (Fig. 6).

1.4 - Friction bolts

Friction bolts are thin, hollowed metal profiles in close contact with the rock

over their entire length. This allows them to be held in place by friction. They

are immediately efficient.

The friction between the ground and the bolt can be provided in two different

ways:

• Either by hydraulic expansion of the profile in the borehole, using pressurised

water injection within the closed tube profile (Fig. 7).

Nut Flat plateCoupler with centre stop enabling direct end-to-end bearing between rods thereby minimizing energy loss during drilling

Fig. 4 - Diagram of a self-drilling bolt, type MINOVA SDA®.

The anchor rod made of high-qualitytubes with continuous cold-rolled drillthread (standard left-hand rope or trapezoidal thread)

Domed platemade of cold-formed flat steel

Protection tube if required Grout

Various drill bits enablequick drilling of boreholes

in diverse soil and rockconditions

Injection hoses and vent

Mechanical anchoragesystem

Steel rod

Bolting drill hole filledwith grout or mortar

Fig. 5 - Schematic diagram of the mixed bolt.

Fig. 6 - Diagram of a self-drilling friction bolt.

1. Friction bolt2. Anchor plate3. Drill bit

4. Drilling rod5. Strike ring6. Sleeve

Steel expansion tube

Bearing plate

Fig. 7 - Diagram of a Swellex® type bolt.


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• Or by forced pushing of a split tube in the borehole, with the initial diameter

of the split profile being greater than that of the hole (Fig. 8).

The friction bolt works by rubbing against the hole walls. In the case of the

Split Set®, the possibility of injecting and bedding the profile increases the

anchor’s capacity.

1.5 - Sliding and other types of bolts

There exist sliding bolts adapted to the brutal rock burst conditions.

These can be mixed type bolts

such as “Cone Bolt®”: The forces

produced by the brutal deforma-

tion of the rock are transferred to

the rod via the anchor plate. For

these forces to attain the opera-

tional distributed anchorage limit,

a special rod coating allows for

greater sliding.

The sliding of the rod in the bedding results in the punching of the grout by

the anchor and permits a bolt movement that retains its efficiency (Fig.10).

Other systems aiming to absorb brutal rock deformations have been developed

using, for example, the deployment of angled elements forming several

segments of the “D-Bolt®” rod (Fig.11).

1.6 - Face bolting

This technique is used to anticipate a deformation of the working face. The

bolts are positioned perpendicular to the face.

The resumption of tunnelling in the bolted face requires the use of easily

destructible bolts. These are generally in fibreglass and sealed over their entire

length using cement grout.

For geotechnical and site reasons, these are generally very long bolts: 1.5 to

2 times the diameter of the excavation. As the works progress, the bolts are

installed in such a manner as to maintain an overlap over approximately a

third of their length.

1.7 - Raft bolting

In certain cases, rafts can receive reinforcement provided by radial type bolting,

metal bolts or fibreglass bolts for excavations carried out in several phases in

swelling ground.

Fig. 8 - Diagram of a Split Set® type bolt.

Fig. 9 - Diagram of the Cone Bolt® type mixed bolt.

Fig. 10 - Diagram showing the operation of the "cone bolt®".(based on McKenzie, R, Use of Cone Bolts in Ground Prone to Rockburst, Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2002).

Fig. 11 - Diagram of the D-Bolt® type bolt.

Before rockburst After rockburst

2 - Drilling-

Type of bedding LocalFriction

Resin MortarSplit Set® Swellex®

Nominal diameter (mm) 31 to 80 28 to 37 28 to 37 20 to 32 20 to 32

Drilling diameter (mm) 32 to 89 33 to 46 32 to 45 28 to 41 38 to 64

In accordance with the manufacturer’s recommendations, the recommended drilling diameters are as follows:


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For bolts bedded in mortar, the drilling diameter depends on the quality of the

ground and the length of the bedding. It varies between 1.5 to 2 times the rod

diameter.

For bolts bedded in resin, it is necessary to pay attention to the drilling per-

formance to respect the optimum cover for the bolt rods.

2.1 - Drilling techniques

In “normal drillability” ground, being one that can be drilled without excessive

wedging or loss of fluids, and within which the holes can be left open for the

time needed to install bolts without any deterioration, the main drilling methods

are as follows (Fig. 15 and Fig. 16):

2.1.1 - Rotary percussion drilling (rotation fracturing)

Rotary percussion drilling (Fig. 12) is generally carried out using “jumbos”

equipped with hydraulic drills. The tool is a bar with a drill bit screwed onto

the end.

A manual method using pneumatic hammers allows small diameter holes with

a limited length to be drilled.

2.1.2 - Rotary drilling (with scaling)

The rotary drilling boring rigs (Fig. 13) do not have a striking system. The drill

bit generally has two tungsten carbide or polycrystalline diamond inserts.

This method, reserved for certain types of ground, is highly productive and

permits relatively small drilling diameters.

2.1.3 - Other drilling methods

2.1.3.1 - Rotary – rotative drilling by grinding (Fig. 14)This drilling method, which uses a tricone bit as a tool, is for large diameters

holes not used for bolting.

2.1.3.2 - Down-the-hole hammer drillingThis type of drilling, not much used for bolting, is reserved for large hole dia-

meters. This type of hammer transmits the percussion energy straight through

to the drill bit without the intermediary of rods. These are compressed air ham-

mers and have standard dimensions ranging from 80 to 500 mm.

Fig. 14 - Rotarydrilling bit.

Free surface

Crushed zone

Fractured zone

Movement direction Impact force

Rock

Fig. 12 - Rotary percussion drilling.

Drill bit

Movement direction

Cutting of a slice by shear force

Rock

Fig. 13 - Rotary drilling. Fig. 16 - Eimco-Secoma Nomagram no.2.

AFTE

S A IN

abra

sivi

ty ra

ting

AFTES DU hardness rating

Rota

tive

drill

ing

area

AVER

AGE/

STRO

NG T

HRUS

T

Rotative drilling

areaSTRONGTHRUST

Rotative drilling areaAVERAGE THRUST

Drilling areaSTRIKING

Fig. 15 - Eimco-Secoma Nomagram no.1.

AFTE

S ra

ting

unia

xial

RC

com

pres

sion

resi

stan

ce

Drilling diameter in mm

Rotation

Rotary

down-the-holehammerHammer outside

hole

Bolting area

Two-lipped PCDdrill bit

Two-lipped tungstencarbide drill bit


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2.1.4 - Summary: indicative data applicable to bolting

2.1.5 - Tools

Drilling tools comprise drill bits, rods and connection accessories (couplings,

fittings, etc.).

For standard bolting, the holes to be made have small diameters (less than

50 mm) and lengths of no more than 4 to 6 m. As from 6 m, the bars shall be

coupled and have much larger drilling diameters.

2.2 - Drilling works

2.2.1 - Removal of cuttings

To remove cuttings in tunnels, drilling using water injection is preferred over

foam or compressed air.

The hole is cleared either by cleaning out and/or blow-out using compressed

air when the bar is removed. Cleaning is necessary for all ground reinforcement

systems. However, it is necessary that cleaning be carried out very carefully

in the case of sealed bolting and, in particular, resin sealings.

2.2.2 - Drilling machines for bolting

Expressed simply, the installation of a bolt requires three stages:

• The drilling of a bolt hole

• The installation of the bolt

• The tightening and/or sealing

There are several possible ways to mechanise the installation of the bolts and

several levels of mechanisation.

It is possible to use the same “jumbo” for drilling both blast holes and bolting

holes (Fig. 17). These “jumbos” can be equipped with telescopic guides to

adapt the drilling lengths to the blasting and bolting boreholes. The equipment

can be provided with articulations to ensure that the (radial) bolt can be posi-

tioned with perfectly adapted kinetics.

However, the current trend is towards drilling further with parallel blast holes

and using jumbos with two or three arms. However, the kinetics of the arms

permitting deeper drilling then becomes incompatible with the radial drilling

of bolt holes. To that end, specific machines are now available, either with

mechanical drilling and manual positioning, or that completely automate the

process for positioning the bolts.

There are therefore machines equipped both with an arm provided with a

drilling guide for blasting and a cradle arm from which the operators install

the bolts.

There are also rock bolting rigs that fully mechanise the installation operation.

These are equipped with a guide on which is positioned the drilling tools, a

bolt rack and the mechanism for installing the bolts. The magazine is generally

limited to 10-12 bolts (Fig. 18). The size of the plates that can be positioned

in the rack is limited. There are also racks and installation systems suitable

to several types of bolts.

Currently, automated rock bolting rigs are used for:

• Local mechanical anchor bolts

• Distributed anchor bolts, resin sealed

• Split Set® type friction bolts

• Swellex® type friction bolts

For mechanical anchor bolts and resin sealed distributed anchor bolts, the bol-

ting turret is equipped with a rotative device to tighten the bolt or turn the rod

in the resin. Certain automated bolting rigs permit the simultaneous placing

of a mesh.

For Split Set® type friction bolts, the rotative device is replaced by a hammer.

For Swellex® type friction bolts, it is replaced by an insert and an end fitting

permitting the injection of water into the bolt.

Depending on the machinery and type of ground, it is now possible to econo-

mically drill boreholes with diameters ranging from 32 to 89 mm for standard

lengths of 4 to 8 m with a potential bar lengthening operation. It is therefore

in this “range” of boreholes that bolting should preferably be used. The choice

Fig. 17 - : Mixed drilling / bolting arm.

Fig. 18 - Bolting turret.

Drilling methodStandard min.

diameterStandard max.

diameterCommentaries

Rotary percussion drilling (drill bits) 32 mm 89 mm Ø max = 127 mm


Ø min = 24 mmLength limited to 3 m


Possibility of 15 m longholes


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of the type of bolt to be installed helps in specifying the type of drilling to be

envisaged, especially in terms of diameters.

Given the overall dimensions, especially of the rock-hammer and hoses, it

is important that the length of bolts that can be installed in a gallery of a

given size be determined during the design phase. Depending on the equip-

ments used, the length of the boom is equal to the length of the bolts plus

1 to 2 m.

2.3 - Special works

In ground that is “difficult to drill", it is necessary to either envisage drilling

with pipe driving, or to use bolts from the self-drilling range.

It is also possible to envisage using a grout type borehole fluid during drilling.

For these special applications, non-standard machines specially equipped for

these works are used.

3 - Bolts-

3.2 - Tip or anchorage device

This term designates the end of the bolt at the end of the borehole.

Its function varies according to the types of bolts considered:

• Straight cut for bolts sealed by injection.

• Tip or bevelled cut for cartridge sealed bolts: it permits the piercing of the

resin or mortar cartridges and favours a good mix.

• Truncated cone end with reduction of diameter to simplify the introduction

of friction bolts.

• Equipped with a drill bit, it permits the hole to be drilled for self-drilling

bolts: the various versions of the drill bits can be treated or equipped with

carbide inserts or teeth in the form of a cross, an arch, etc.

• Equipped with a shell, it provides local anchorage for the bolt: these ancho-

rages are formed from a central plug into which, depending on the contact

surface being sought on the borehole wall, between 2 and 6 leaves are

inserted. They are constructed from steel or an aluminium alloy. Traction

exerted on the rod causes the shell to expand. The choice of type of shell

must be adapted to the geological conditions encountered and be validated

by tests (see § 6).

3.3 - The head

This term designates the projecting end of the bolt that permits the inter-

locking of the distribution plate and the bolt.

In most cases of local anchor bolts or distributed sealing bolts, it has a thread

of between 100 and 200 mm receiving a hexagonal coupling nut. These

threads can be trimmed but are generally rolled. The type of threading can

have an influence on the bolt capacity.

There can also be specific versions:

• Forged hexagonal heads to allow the rotational drive of resin sealed HA rods

or to reduce the projecting part of local bolts. In this case, the bolt is tightened

by rotating the rod in the anchorage head.

• Threaded ends completed by a rotational drive device for the HA rods, such

as flats and driving squares, resined or forged feed nuts, rivet or pinned

nuts.

In the case of self-drilling or threaded profile steel bolts, or in the case of glass

This chapter is devoted to the properties of the bolt, including its accessories

and particularities (thread, flanges, head, and bearing plate).

The following must be defined for each type of bolt:

• The materials used for the rod and its accessories

• The mechanical characteristics of the rod and its accessories (see §3.1)

• The geometrical characteristics of the rod and its accessories

The main materials used are steel alloys, fibreglass or, exceptionally, carbon

fibre. The choice of materials used must be adapted to the sought-after per-

formances (elastic limit, elongation at rupture, destructibility, etc.).

3.1 - The rod

This is the central part of the bolt. Depending on the type of bolt, it either has

a solid or hollow section.

The rod can be smooth in the case of friction bolts and local anchor bolts or

ribbed in the case of distributed sealing bolts. In the latter case, the flanges

improve the mixing of the sealing resin and thus the sealing itself.

It is also worth mentioning the bolt whose flanges provide a continuous thread

and permit the length to be adjusted on site (GEWI® type bolt).

In the case of self-drilling bolts, the rod can potentially be formed from several

elements connected by a threaded sleeve.

The standard thread profiles are:

“chord” type (the most common) “T” type

The “chord” type thread provides a good seal around the sleeves. The “T” type

thread makes unscrewing easier.

Non-standard thread profiles are also used.

In the case of bolts made from composite materials, all types of sections can

be used.


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fibre bolts with threaded profiles, the bolt heads are simply equipped with

a nut.

Friction bolts either have a ring or a welded end fitting that bears on the

anchorage plate installed prior to prior to driving the bolt.

3.4 - Distribution plate

The bearing plates (Fig. 19) represent an important support element and can

be used independently or in association with mesh, straps or brackets. They

provide a containment of the rock mass at the head of the bolt.

It is also possible to use metal sheeting to increase the bearing surface of

these plates.

There are three main types of plates:

• Rigid plates dimensioned in such a way as to provide static bearing points

when compared with the bolts with which they are associated.

• Flexible or self-compensating plates permitting gradual deformations in

function of the loads on the bolts.

• Special plates for injection, doubling up to hold the mesh, and reinforce-

ment (“spider” type).

through the intermediary of the head, with tightening of the nut using an impact

wrench or, where required, a torque wrench. The tightening torque must be

adapted to the type of bolt and nut.

The dished plate permits a certain adaptation to deformation.

An auxiliary plate, clipped or screwed to the threaded bolt head, is generally

used to attach the reinforcement mesh or nets when this type of system is

used in addition to the bolting.

The use of the bolter and a storage turret calls for the use of plates with

dimensions adapted to the equipment (≤15x15cm). This can be unfavourable

for the mobilisation of the ground cone at the top of the bolt and the connection

with the facing.

For glass fibre bolts, the plate can be held by a wedge inserted into the head

of the bolt separating the blades or the two parts of the bolt. However, this

procedure does not provide optimal tightening. There are also cylindrical glass

fibre bolts with threading on the head that permit the fixing of a plate through

the use of a nut. In general, the head of the glass fibre bolt represents a low

resistance area.

3.5 - Corrosion protection

When the operational duration of the support makes it necessary, corrosion

protection can be provided:

• Continuous mortar, grout or resin sealing

• Excessive thickness of the parts

• Hot dipped galvanisation of the parts

• Epoxy protection (hot painted)

• Coating by cold bituminous dipping

• Injected sheathed bolts (Fig. 27)

• Stainless steel bolts

3.6 - Useful dimensioning characteristics

In agreement with the recommendations of the AFTES (GT 30) work group on

“the design and dimensioning of radial rock", the main mechanical characte-

ristics useful for the dimensioning of bolting, and dependent on the types of

bolts and manufacturer references, are as follows:

• The resistance of the rod in traction at the yield strength, in kN

• The resistance of the head (plate fixing system) in traction at the elastic limit,

in kN

• The resistance of the rod at breaking strength, in kN

• The resistance of the head (plate fixing device) at breaking limit, in kN

• Relative elongation of the rod in traction at the yield strength, in %

• Relative elongation of the rod at breaking strength, in %.

These characteristics, obtained by laboratory traction tests on all or part of the

elements forming the bolt on completion of the manufacturing process, must

be guaranteed (“minimum guaranteed value”) and are independent from

installation conditions (drilling, sealing, etc.).

Rigid plates Adjustable jointed plates

Fig. 19 - Examples of plates.

Distribution plate for injected bedding

Injection Évent

Spider plates

The bearing plates usually have 15 to 20 cm sides and are 4 to 10 mm thick.

They are either flat, dished or jointed with a circular or oblong hole. This permits

a better adaptation to the effective angle of the bar and nut borehole.

For friction bolts, the plate is immediately operational without tightening.

For local or distributed anchor bolts, the plate is tightened against the facing


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The rod characteristics can theoretically be ascertained from the geometrical

characteristics of the bolt and the mechanical characteristics of its parts, such

as:

• The resistant section of the rod, in m²

• The elastic limit stress at the traction strength of the material, in MPa

• The elastic deformation module (Young module) of the material, in MPa

• The maximum tensile stress of the material, in MPa

• The deformation at maximum tensile stress, in %

These characteristics are theoretically accessible with a HA B500B bolt, (HA

= High Adherence, B = Bar, 500 = elastic limit in MPa, B = ductility rating)

but need to be adapted for more specific bolts such as friction bolts and mixed

bolts. This is why it is always better to privilege the knowledge of characte-

ristics that can be directly measured on the bolt.

Bolting in a rock mass also implies the mobilisation of the shearing charac-

teristics of the bolts, in other words under the action-effect of relative move-

ment transversal to the rod axis. This would seem to be a complex operation

involving the combined characteristics of shearing and the traction of the bolt

itself, as well as those of the rock and, where applicable, the sealing

product.

No standardised test exists to characterise this operation but a number of

experimental or theoretical approaches are underway.

4.1 - End-anchorage or mechanical anchorage

The anchorage of the bolt is carried out using a shell that generally comprises

2 to 6 leaves and a central plug. A threaded rod is inserted into the groove (Fig.

20 and Fig. 21).

The shell branches are spread during the tightening of the bolt. The shell

wedges are positioned up against the hole walls and the rod is prestressed.

The bolt is installed by tightening the coupling nut located on the plate to a

torque recommended by the manufacturer.

The choice of the type of anchorage depends on the nature of the rock and

should be decided in accordance with the results of preliminary tests.

The anchorage depends on the following parameters:

• The quality of the rock around the anchorage point (min. compressive

strength): below a compressive strength of 10 MPa, it is necessary to use

special shells. In this case, local anchor bolting is not recommended

•The shell surface in contact with the ground: it progresses in inverse propor-

tion to the ground strength

• The materials forming the shell

• The respective diameters of the shell and the drilling hole

• The initial tightening of the nut

The main advantage of local anchorage is to produce an immediate contain-

ment after installation and thus immediate safety. Its installation is simple and

fast.

During installation, the adequate tightening of the bolt should be checked

alongside making sure that the plate is in very close contact with the ground.

Time and/or vibration caused by blasting can result in scaling around the plate.

The efficiency of the bolt is reduced to zero if the plate is no longer in contact

with the ground.

Where possible, it is worthwhile checking and retightening the plate at least

once.

4.2 - Resin or grout sealing


Resin permits the sealing of the bolt over its entire length. This type of sealing

4 - Anchorages-

PlugShell

rod

Fig. 20 - Operating principle for mechanical anchorage.

Two branches Six branchesThree branches

Fig. 21 - Examples of expansion shell.


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is only adapted to rock permitting a good anchorage hole calibration. There

are “fast” and “slow” resin setting times.

The resin is generally provided in the form of cartridges containing a catalyser

and a hardener (Fig. 22).

Currently, given the materials available and the high viscosity of the resins,

the mechanical installation of the sealed bolts can be carried out over a length

of up to 5 m. This limit is imposed on the resistance of the resin during mixing.

The resin hardening time, and thus the sealing, is generally between 5 and 15

min (depending on the product and the temperature) and provides this type of

bolt with extremely rapid efficiency. This is a vital choice factor for the type of

bolting used.

The important parameters for installing the resin bolt are:

The diameter of the bolt hole and its good performance over the entire length

The annular space between the hole and the chosen rod (Fig. 23).

• The cleaning of the hole which must have had all borehole residues (cuttings)

removed

• The depth of the hole: excessive depth will result in an increased consump-

tion of resin and inefficient mixing

• The resin loads must be introduced and pushed to the rear of the hole and

the position of the loads in the hole must be checked. A parachute can be

used to retain the resin loads in the hole while awaiting the introduction of

the rod

• The installation of the bolt must comply with the supplier’s recommendations.

The various stages in the procedure are as follows (Fig. 24) :

- The introduction of the rod, turning it while pushing it towards the rear

of the hole

- Mixing: maintain the rotation of the rod once it has reached the rear of

the hole to permit a good mix between the resin and the hardener

- Tightening once the resin has set

Using an automated rock bolting rig, the introduction of the cartridges in the

hole is generally carried out using a compressed air “blowpipe”. This requires

a hole that is clean and free from any elements that might damage or prevent

the installation of the cartridges. This is often the most delicate aspect of the

installation sequence.

The following parameters must be checked:

• The mixing time which depends on the type of resin: insufficient time will

not allow the resin to harden in a proper manner, but an excessive mixing

time will impair the polymerisation of the resin and consequently the satis-

factory anchorage of the bolt.

• The rotation speed which needs to be checked and the mixing time must be

adapted to the envisaged speed.

• The installation temperature influences the resin setting time.

The storage of the resin cartridges must be taken into consideration when set-

ting up and managing the work site:

• Storage life is short: maximum of a few months at an average temperature

of 20-25°C. This storage period reduces if this average temperature is not

maintained. It is recommended that the stock be rotated.

• The storage temperature must not fall below 0°C.

• The cartridges should preferably be stored in a cool, dry environment pro-

tected from direct sunlight.

• During installation procedures, if the storage temperature is too different

from the installation temperature, it will be necessary to leave sufficient time

for the resin temperature to attain that of the installation temperature.

• The elimination of residues and waste must use adapted channels.

The resin cartridges are delivered in boxes containing 20 units. The packaging

shall bear at least the following information:

• Supplier / Origin

• Type of product and contents of individual cartridges

• Pictograms and, where applicable, safety notices

• Date of manufacture

• Expiry date

• Lot number

For certain applications, the resin

can be injected by pumping.

Catalyser

Resin

Fig. 22 - Resin cartridge.

Diameter of drill hole D

Annular space e

Diameter of rodd

Fig. 23 - Annular space between the hole and the rod.

Fig. 24 - Stages for the installation of a resin bolt.


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4.2.2 - Mortar or grout sealing

This sealing product takes the form of mortar cartridges, dry mortar in sacks

or pumpable grout.

The mortar used (cartridge or sack) incorporates a high resistance, rapid set-

ting cement. For the grout, the sand used must be fine to be pumpable. Unless

expansive, its shrinkage must be limited.

The cement, additives and water based grout is generally more liquid and its

installation more complicated than the mortar-based operation. It can be pre-

pared on site

Parameters to be checked for grout or mortar specifications:

• The setting times must be adapted to the required work

• The product thixotropy must permit pumping

• The product must be of the limited shrinkage type and even be slightly

expansive

• The steel corrosion protection must not be attacked by the product

• Mechanical compression and bending

4.2.2.1 - Pumped anchorage mortarsPumped mortars are mixes specifically prepared for the work site or dry pre-

mixed, ready-to-use and prepared by the formulators.

The ready-to-use mortars have had additives added and generally have cha-

racteristics that make their installation easier and improve the quality of the

anchorage: thixotropy, lack of shrinkage, pumpability. They can provide rapid

hardening, allowing the bolts to be tensioned after 4 or 5 h depending on the

objectives being sought. At 24 h and depending on the product, strengths can

attain between 15 and 35 MPa.

Standard installation procedure:

a) Preparation of the mortar:

- Mixing of the mortar in compliance with the manufacturer’s recom-

mendations, especially insofar as the quantity of water is concerned

- Mixing

b) Mortar injection using a pump, filling from the base of the hole towards

the head:

- An injection hose is introduced to the rear of the hole

- The mortar injected by the pump pushes the hose towards the exterior.

There must be a certain resistance to the rising of the hose to ensure

the filling of voids and gaps

c) Introduction of rods simply by pushing:

- The introduction of the bolt permits the distribution of a certain quantity

of mortar in any gaps in the ground

- At the end of the operation, the mortar should normally come out at

the head of the bolt via the annular space between the rod and the

hole

- A wooden wedge is occasionally used to maintain the bolt in the hole

during the setting of the sealing (for sub-vertical bolts)

d) Tighten the bolts once the mortar has set: the mortar setting time depends

on the characteristics of the chosen product and the installation tempera-

ture.

Injection after the installation of the bolts can also be envisaged.

The parameters influencing the installation of the sealing products are:

• The time between the mixing and the installation (max. 15 to 20 mn), which

depends on the ambient temperature and the temperature of the mixing

water

• The time between the injection and the installation of the bolt bar

• The ambient installation temperature and the rock temperature. Installation

is not recommended if the temperature is too low (below 5°C)

• The water dosage

4.2.2.2 - Composition of site mortarsFor basic mortars prepared on side, the weight batched dose is as follows:

• 1 cement

• 1 sand (0-3 mm or less)

• 0.3-0.35 (water/cement)

It is possible to obtain mortars presenting considerable early strength by

using rapid setting hydraulic binders (Vicalpes® type) or quick-setting

cement.

Example of a one hour quick-setting mortar composition:

• Sand 0-2mm: 55%

• Filler: 11%

• Vicalpes® R 17%

• CEM I 52.5 R 17%

• Water

• Additives

This mortar has a strength of 6 MPa at 3h and 18 MPa at 24h.

4.2.2.3 - Anchorage mortars in cartridgesThe cartridges contain a ready-to-use dry mortar packaged in permeable

packing permitting water absorption. Their use is limited to small quantities

of bolting works and for short bolts. The cartridges are positioned by tamping

(rammer). The bolts are then introduced by being simply pushed in.

4.3 - Hydraulically expandable friction bolts

These bolts are steel folded in on themselves. They are introduced into the

hole and then inflated using high pressure water.

The expansion pressure for the installation is around 30 MPa. It is necessary

to check its compatibility with the quality of the rock. In all cases, it is essential

Type of mortarSetting time

(à 20°C)Rc 2 h Rc 1 day Rc 1 day

Fast 28 - 30 min 5 -10 MPa 20 - 35 MPa 35 - 70 MPa

Standard 1 - 2 h 25 - 40 MPa 35 - 70 MPa

Slow 4 - 8 h 25 - 40 MPa 35 - 70 MPa


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that it be defined and described in the site bolting procedures (preliminary tests).

The high pressure inflation pumps must be inspected and revision works car-

ried out on a regular basis.

Bolt installation procedure (Fig. 25):


• Insertion of the bolt in the hole, connection to the inflation hose

• Inflation, between 30 s and 1 min

• End of installation

Parameters influencing the anchorage:

• Quality of steel used: there are two main qualities of Swellex® type bolts

(standard range and manganese range)

• Corrosion resistance: it is possible to obtain bolts with an anti-corrosion finish

• Quality of the tube manufacturing process and the end welds

• Water injection pressure

• Quality of the rock in the ground: this type of bolt is adapted to a ground

whose resistance is compatible with the inflation pressure. For other types

of ground, sleeves are used to avoid damaging the ground near the head of

the hole

The drilling diameter is checked for each type of bolt and in compliance with

the manufacturer’s recommendations

4.4 - Driven friction bolts (forced)

These friction bolts take the form of a steel tube with a high elastic limit, slotted

along its full length.

Characteristics of the friction bolt:

• Easy installation (by percussion hammer)

• Active and dynamic friction reinforcement system. The bolt controls the

expansion of the ground thanks to its considerable elongation and failure-

free shearing

• Corrosion resistance: hot-dipped galvanised bolts can be obtained

• Currently, its length is limited to around 4 m



• Insertion of the bolt equipped with its plate in the hole

• The hammer is positioned and the bolt thrust into the hole. The thrust must

be maintained until contact is made between the plate and the facing

Parameters to ensure the satisfactory positioning of the friction bolts:

• The drilling diameter must be checked and the supplier’s recommendations

respected

• Ground characteristics: this type of bolt reveals its efficiency in fractured

ground where it can maintain the position of the blocks

• The quality of the water in the massif influences the durability of the bolt

The installation of the bolt is relatively simple, and this represents its main

advantage.

4.5 - Mixed anchorage

There are several mixed anchorage bolt combinations. Generally speaking,

the aim is to obtain the advantages of an immediate anchorage guaranteed

by an expansion shell, and the long-term resistance of a distributed anchorage

bolt.

While this is often a combination of local and distributed anchorages, other

combinations exist, such as:

• End-anchored bolt + injection of resin or cement between the hole and the bolt

• Friction + injection of cement in the bolt tube

4.5.1 - End-anchored bolt + cement Injection

It is possible to simultaneously obtain the advantages of a mechanical ancho-

rage and a distributed anchorage by using mechanical anchor bolts with a

subsequent injection of a resin or cement grout into the bolt hole.

Fig. 25 - Installation of a expandable rock bolt.

© A

tlas C

opco

Fig. 26 - Installation by thrusting of a friction bolt.

© M

etal S

ervic

e

Drilling- 35 à 38 mm (SS39)- 41 à 46 mm (SS46)

Installation

Bolt installed- Radial forces- Considerable

plate pressure


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Certain types of bolts have a hollow rod into which the sealing product can

be injected (as per self-drilling bolts) between the bar, the local anchorage

and the ground. Other bolts (CT Bolts®) permit the injection of the sealing

product between a PVC casing and the bolt rod up to the head of the ancho-

rage (Fig. 27).

4.5.2 - Friction + cement injection or filling

The thrust friction bolt (§ 4.4) can be injected with a mortar or grout after ins-

tallation.

There is also a percussion type of thrust driven friction bolt that can receive

cartridges containing a slightly expansive cement-based binder (Fig. 28).

When setting, the cement produces a pressure on the tube forming the bolt

and reinforces its keying in the ground, thus increasing the force needed to

slide the anchorage (10 to 15t/m).

Fig. 28 :- Example of a mixed anchorage (friction + cement injection), injected Split Set® type.

4.6 - Self-drilling bolts

4.6.1 - Steel bolts

Self-drilling bolts are formed from hollowed rods, equipped at their base with

a lost drill. Having drilled with the fluid returning through the annular gap, grout

is then injected via the rod providing the bolt sealing.

These systems directly replace the drilling bar and the drill bit. They are des-

igned to be positioned alongside standard rotary percussion machinery.

As the anchorage is of the distributed type, the factors influencing the quality

of the anchorage will be the same, although with certain additional difficulties:

the diameter of the drill bit must be sufficiently small to allow the annular

space to have a good mortar or grout sealing. However, it must also be suffi-

ciently large to permit the good evacuation of the cuttings.

Water, air or grout drilling is possible.

Although not widely used, it is possible to envisage a sealing

using a pumpable sealing.


• Drilling of the hole using the bolt rod

• Potential adding of a length through the use of a sleeve

• Injection

• Installation of the plate

4.6.2 - Glass fibre bolts

Glass fibre self-drilling bolts are available. Their main advantages are:

• They are injectable

• They are not heavy

• They do not suffer from corrosion

• They are easily destructible and therefore well adapted for temporary

supports in areas that will subsequently be excavated.

They are installed in the same way as the rotary drilling method.

4.6.3 - Self-drilling friction bolts

This type of bolt operates in the same way as the pipe driving method, but in

this case, the pipe is split, similarly to the rammed Split Set® type friction bolt.

The hammer, used for the drilling, also pushes the pipe into the hole, resulting

in a friction anchorage immediately after its installation (Fig. 30).

Fig. 27 - Example of the installation of a mixed anchorage bolt, CT Bolt® type.

Fig. 29 - Installation of a self-drilling bolt.

Fig. 30 - Procedure for the installation of a self-drillingfriction bolt (DSI®).

Power Set drill bit

AT - Pc

Power Setdrill

Power Set adapter

© A

tlas

Copc

o


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Once a type of bolting is chosen, the contractor needs to respect a certain

number of conditions to ensure that the installation of the bolting elements

takes place as safely as possible.

The bolting takes place after the purging of the walls and the face, or after the

application of a first layer of containment shotcrete.

5.1 - Reference texts

The "Guide des bonnes pratiques pour la Sécurité et la protection de la Santé

lors de travaux sousterrains" (guide to good safety and health protection prac-

tices when carrying out underground works) published by CARSAT-RA is a

reference document used by the client, the project manager and the contractor

to draw up engineering and site works documents relative to safety (SPS,

SSHPP, Procedures, etc).

Reminder of the logic to be respected for the implementation of the PGP (gene-

ral prevention principles) such as defined in article L 4121-2 of the French

Labour Code:

• Avoid professional and environmental risks

• As far as possible, evaluate unavoidable risks

• Privilege inherent protections by using operational methods adapted to the

workplace, using adequate equipment and materials and always take care

to respect the following rule which consists in adapting the work to the labour

force and not the other way round

• Always privilege collective protection systems and, where needed, install

adapted individual protection systems

• Provide personnel with training concerning the risks they are liable to encounter.

5.2 - Risk evaluation and analysis

Bolted support works present various types of risks. They can stem from a wide

range of sources, from the supply of materials and equipment through to the

installation of the support, without forgetting the “inspections” phase. They essen-

tially result from the installation of supports and the monitoring of their behaviour.

Risks linked to the ground must be taken into consideration as excavations

that have not yet been provided with supports present serious dangers, espe-

cially rock falls.

The analysis of the “bolting” activity begins as from the supply of the materials

and equipment. It is a phase during which the workers carry out repetitive

handling tasks that can occasionally call for physical efforts that can lead to

bad posture. The locations of materials and equipment delivery and return

areas shall be organised in such a way that these movements do not cause

any traffic accidents.

The drilling phase can be the source of several risks, some of which linked

to the materials and equipment. They can concern:

• Hand or fingers getting caught while, for instance, installing a rod or chan-

ging drill bits

• Impulsive impacts resulting from vibrations produced by jackhammers

The lack of lighting as well as excessive lighting in work areas can result in risk

situations. During drilling, the noise and dust from an insufficiently equipped drilling

machine can be a source of discomfort and occupational diseases for workers.

The bolt installation phase presents risks that are common to all types of

bolts as well as other risks specific to the types of bolts used. The handling

of the bolt and its introduction in the drilling hole can result in injuries to

hands and impacts resulting from the use of sledgehammers. Concerning

vault bolts, working on a cradle can be the cause of various tools and ins-

truments falling onto lower areas.

The installation of distributed bedded anchor bolts presents risk linked to

the use of injection pumps. The preparation of sealing products can lead to

risks of skin burns, inhalation and even ingestion of dust (fines). During the

injection phase, the breakage of a hose can take place, leading to the same

risks discussed for the preparation phase.

During the installation of local anchor bolts, the risks are essentially linked

to the handling of accessories and the positioning of the anchorage shells,

plates and tightening nuts.

For friction anchorages, the risks depend on the types of bolts. Bolts whose

efficiency is only effective once they have absorbed water, alongside bolts

rammed into the ground, present risks linked to the installation materials

and equipment; with water injection pump for the former and striking system

machinery for the second.

5.3 - Measures to be envisaged

The measures to be envisaged for monitoring the behaviour of the bolts,

whether during the excavation phase or during the working life of the struc-

ture where the supports remain surface mounted, call for inspections.

The stakeholders involved in the construction (specifier, client, project mana-

ger, health, protection and safety coordinator and contractors), as well as

infrastructure managers shall refer to paragraph 6.4 of the present recom-

mendation – “Surveillance des boulons” (bolt monitoring) during the works.

The measures to be envisaged insofar as risks linked to the ground are

concerned are:

• Ground monitoring: assignment of a person responsible for inspecting the

supports

• Systematic preliminary purge, privileging the use of mechanical purging.

The measures to be envisaged with regard to risks linked to materials and

equipment during drilling are:

• Set up training courses covering the use and maintenance of drilling

machinery

5 - Safety during the bolting phase-


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• Ensure that cradles meet the needs of safety regulations and their specific

uses.

• As far as possible, mechanise jobs (when the section and number bolts to

be installed make it possible): delivery of bolts, changing the borehole rods

and bars

• If drilling is carried out manually, provide for supports on which to place

materials and equipment (tripod) and lay out the work space at the base

of the wall to be bolted to avoid any risk of employees falling

• Prevent other employees from approaching: to guard against the risk of

personnel becoming involved in collisions or entanglements next to the

drilling machine should there be a sudden movement of the guide, it is

necessary to define a safety perimeter around the machines as well as

certain safety rules to attract the attention of the operator when someone

enters his working vicinity.

• Avoid generating dust and any projection of materials: privilege water or

air/water mix drilling. In granular ground or ground whose nature presents

health risks, install a dust collection system and ventilation in the work

area.

• Concerning noise: privilege electrohydraulic and soundproofed machinery

and equipment, but without reducing the requirements of wearing indivi-

dual protection gear.

The measures to be envisaged concerning the risks linked to the installation

of the bolt are:

• Privilege the use of bolting robots.

• If the bolting is to be carried out manually, provide training adapted to the

various types of bolts.

• Wear adapted individual protection gear.

6.1 - Testing principles

To ensure bolting quality and efficiency, several types of inspections and

tests can be carried out at various stages.

There are:

• preliminary tests carried out at the project stage to validate the envisaged

bolting system and, in particular, its dimensioning given the quality of the

ground to be bolted (tests that can go as far as pulling out the test bolt)

• suitability tests prior to the works, to check the adaptation of the chosen

bolting system with the installation procedure and the in situ conditions,

especially those concerning the ground

• on arrival on site, a systematic inspection of the various constituent parts

(bolts and sealings) as well as an inspection of the installation machinery

and materials

• inspection tests carried out during works on anchorages forming part of

the support system, to check their efficiency

It is also possible to examine the bolts over time by permanently fixing dyna-

mometric units at the head of the anchorage between the plate and the nut

and to occasionally note the deformation using a comparator.

These inspections and tests are further detailed in the following paragraphs.

6.2 - Inspection of constituent parts

The quality of the various constituent bolting parts (bolts, expansion shells,

self-drilling drill bits and other accessories) and the installation machinery

and equipment shall be inspected:

• During the approval procedure, by checking the laboratory tests carried

out by the supplier (yield load, ultimate load, elongation at failure, especially

for the rods, etc.). The supplier’s inspection reports must be checked on

delivery to the site.

• On delivery and installation: diameter, length, thread, head and tip,

absence of rust, grease, etc.:

- For HA rods whose diameters are set by AFNOR standards (14 - 16

- 20 - 25 - 32 - 40) and thus subject to an approval certificate, it is

essential that the supply be accompanied by a valid description

sheet concerning the NF AFCAB of the supplied steel,

- For HA rods whose diameters are not covered by AFNOR standards

(18 - 22 - 26 - 28 - 30 - 34, etc.), it is essential that the supply be

accompanied by a certificate from the producing steel mill; this docu-

ment shall indicate the data identifying the product (casting number,

chemical analysis, etc.) as well as the yield load values (Re, act), the

tensile strength values (Rm) and their relative “relations”, and finally,

the total elongation (Agt) expressed as a percentage. All this shall be

in compliance with the NF A 85-080-1 (2010-10) standards.

For the friction bolts, it is necessary to inspect the markings specific

to each bolt allowing its traceability, in accordance with the concer-

ned standard,

- All these values determine the mechanical characteristics of the

steel.

• The quality of water and sand used for the mortars,

• The storage conditions for the various constituents.

Concerning the sealing products (resin, grout, mortar), the following shall

be checked:

• For the resins: condition of the cartridges on delivery, expiry date

(generally several months, storage conditions, polymerisation speeds,

etc.

• For the grouts and mortars: compressive strength at 7 d and 28 d, vis-

cosity, setting times: six test samples at the injection lance outlet for

each shift,

• For mortars in cartridges: condition of the cartridges on delivery,

storage conditions.

6 - Rock bolting testing-


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It is necessary to cover oneself against the risk of counterfeits:

• Traceability

• Marking

• Standardisation system

• Compliance certificate

In addition, it is necessary to ensure that the quality control covers all the

bolt manufacturing stages and that the test bolts are the same as those that

are installed.

6.3 - Operational methods for bolt tensile and pull-out tests

Concerning inspection tests for mortar sealed bolts:

The test result will depend on the setting of the sealing grout as well as on

the convergence and “tightening” of the bolt following an increase in the

ortho radial stress.

The test should therefore be carried out when there is a low convergence

speed:

• under low cover: 3 mm/day

• under strong constraint: 1-2 cm/day

6.3.1 General principles concerning bolt tests

The tensile and pull-out tests carried out on the bolts generally use a hollow

cylinder that allows the bolt head to be pulled by resting against the rock

wall around the anchorage bearing plate (Fig. 31).

For the mechanical anchor bolts, tests can be carried out with the torque

wrench used to place them in tension.

The movement of the bolt head is measured using a comparator. This makes

it possible to trace the load-movement curve characterising the behaviour

of the bolt and its anchorage.

Tensioning is carried out in stages. At each stage, the changing displacement

or tension loss if applicable, defines a tensile creep resistance (or slipping)

of the anchorage. It is therefore possible to define a peak resistance and, in

certain cases, a residual resistance.

The preliminary tests and suitability tests are to be carried out on specific

anchorages that do not form part of the structure support system or that do

not participate in the stability of the operational structure.

For open-air supports, the preliminary tests and suitability tests are generally

destructive in order to measure the resistance of the sealing necessary for

the dimensioning of the support. However, preliminary tests and suitability

tests are not necessary underground. They are carried out in the same way

as the inspection tests and in the same bolt and ground conditions as those

for the structure where they will be used. (see below).

However, in certain cases, the Engineer can ask for destructive tests in order

to evaluate the Tu (in kN) resistance of the anchorage in the ground. This is

generally in function of the anchorage length (or qs expressed in kPa which

is the conventionally agreed lateral friction).

The number of tests to be carried out per type of anchorage and by type of

geological conditions is to be set in the contract specifications. The average

strength is often defined on the basis of a minimum of five tests per type of

anchorage and by type of geological conditions. This is because a fairly wide

dispersion is generally observed.

The preliminary tests and suitability tests result in a test report.

The inspection tests are to be carried out on anchorages forming part of the

structure support system. An inspection is carried out to ensure that the

anchorage resists a test tensile strength defined during the design phase

and which is in function of the bolt’s tensile strength service limit (generally

test tensile strength = tensile strength service limit or rather 1.2 x tensile

strength service limit).

For an anchorage with immediate efficiency, testing should be carried out

rapidly after its installation.

For mortar or resin sealed bolts, testing must be carried out as soon as the

setting of the sealing allows it (7 to 28 days for the mortar, 8 to 24 hours for

the resin, in accordance with information provide by the supplier and in

accordance with contract requirements).

Deferred testing can also be carried out to check the service life of an ancho-

rage (see § 6.4).

6.3.2 - Standards and recommendations

For anchorages bedded into the rock (mortar or resin), the pull test procedure

as well as the testing procedure is described by the XP P 94-444 (December

2002) standard – Static pull test under an axial traction load for an anchorage

sealed in a rock mass – Staged tests:

• The bolts are tensioned by incremental loads and/or movements and mea-

sures are taken at each increment once the load and movement have been

stabilised (noting the stabilisation period). The stages are set at 5 minutes.

• The breaking strength test comprises two loading/unloading cycles per

stage, with the 1st cycle up to the estimated stress limit and the 2nd cycle

up to twice this stress. The test provides the Tu limit traction force asso-

ciated with the length L of the reinforcement bedded into the rocky mate-

rial.

• The inspection test (Fig. 32) is carried out over a single load cycle subdi-

Fig. 31 - Tensile test system.


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vided into five 5 minute stages until Te is obtained followed by an unloading

over three 1 minute stages (see figure 2). It might also be necessary to

maintain the last Te stage over a longer period (20 or 30 minutes) prior

to carrying out the inspected unloading. The test is deemed conclusive if

the average resistance of the tests is greater than either Ts or 1.1 times

Ts (in accordance with contract requirements).

The ISRM recommendation and the ASTM standard use similar methodologies.

They are described up to the pulling out of the anchor. Their references are as

follows:

• ISRM – Suggested Method for Rockbolt Testing (1975),

• ASTM D 4435-84 (reapproved 1998) – Standard Test Method for Rock Anchor

Pull Test.

In the case of breaking strength tests, measures must be taken to:

a) Avoid breaking the reinforcement under the effect of maximum traction:

- by choosing a sufficient section

- and/or limiting the length of the sealing; however, the latter must be

sufficient to absorb all unevenness in the ground

b) Limiting the edge effects:

- either by providing a minimum free length when bolt sealing (around

1 m in the ground and 0.5 m in the rock)

A check of the non-sealed length of the anchorages is carried out by introducing

a rod in the annular space free from any sealing.

- or by having test equipment positioned on the ground around the rock

bolt head, but where all points of the bearing surface are at least 0.3 m

from the edges of the hole

c) for bolts sealed into the rock (using mortar or resin), the test shall take place

after a minimum setting time (7 to 28 days for the mortar, or 8 to 24 hours

for the resin, in accordance with information provided by the supplier and

contract requirements)

The pull tests on the friction bolts are carried out in the same way. They take

place immediately after installation (refer to manufacturer’s instructions). Tests

on several bolt lengths (minimum of three) provide a more reliable evaluation

of the qs limit friction value. The qs value can increase under the effect of

ground movements around the excavation.

Apart from bolts in tunnels, being the subject of the present recommendation,

there are other test procedures concerning micropiles and nails or ancho-

rages in loose ground. This results in adding the concept of creep to that of

tensile strength, alongside anchorage ties. These tests are generally intended

to determine the qs limit side friction value necessary for the dimensioning

of the concerned structures (stability of studded slopes, foundations, etc.)

but can also concern underground structures:

• Large structures

• Works requiring strict deformation inspections

• Proximity of existing structures

• Clayey rock

• Etc.

These procedures are mentioned here as a reminder:

• CLOUTERRE 1991 recommendations

• Controlled movement tensile tests (constant speed)

• Controlled load tensile tests (creep stages)

• NF P 94-242-1 (1993) standard – Static nail pull test subject to an axial

traction load – Constant movement speed test

• ISRM - Suggested Method for Rock Anchorage Testing (1985)

• NF P 94-153 (1993) standard – Static anchorage tie test

• Chapter 6 of TA 95 recommendations

• NF EN 1537 – Anchorage tie works: several test methods proposed in § 9

and appendix E

6.4 - Surveillance of bolts during site works

During the excavation phase, at a distance to the rear of the face determined

according to the vibrations caused by blasting or under the effect of ancho-

rage sliding, it is necessary to check that the nuts are well tightened and,

where required, to carry out a systematic retightening of all the local anchor

bolts. This type of inspection is also recommended prior to the application

of the last few layers of shotcrete or prior to the installation, depending on

the case, of membrane or a concrete lining.

Bolts with broken or breakable heads must be changed or replaced by ano-

ther support system.

As a reminder, it is possible to monitor the tension of a bolt by placing either

a dynamometric packer or a loading cell between the bolt head and the rock.

An overall inspection of the support system represented by the bolting, whether

or not associated with shotcrete, is carried out. It particularly includes conver-

gence methods within the framework of the “interactive design” method, for-

merly know as the “observational method”. Should a behaviour be judged

abnormal, it may be necessary to reinforce the bolting system (increased den-

sity, diameter and/or length of bolts, reduction in the time taken for installation

in relation to drilling progress on the face, choice of another type of bolt, etc.)

or completely modify the support system (such as heavy arches).

Fig. 32 - inspection test. Loading – unloading programme (in accordance with XP P 94-444).

T Traction forceTe Traction force imposed for the inspectiont Time in minutesP Test preparation phase


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If when tensioning a local anchorage bolt or if, after a certain time span,

there is a rock scaling or break-up and that there is no longer any contact

between the anchorage plate and the ground, then the bolt becomes ineffi-

cient and must be replaced.

In structures where the support remains surface-mounted, it is necessary,

to ensure the long service life of the support. To that end, the contractor, up

to the handover of the structure, or the client over the entire working life of

the structure, must perform periodic inspection measures and carry out the

required actions.

Water circulation, flow above all when particularly aggressive, can result in

the steel rusting. This reduces the efficiency of the bolt and its anchorage. In

this case, it is recommended that corrosion protection products are used, or

to use distributed anchor bolts, or seal local anchor bolts over their entire length

once tensioned, and to protect the plate and nut. However, these precautions

in no way replace the need to carry out periodic inspections.

7 - Interpretation matrix-

BOLTS

DATA

Occasionallocal anchorbolts bolts

Distributed anchorage bolts Mixed bolts(occasional

anchorage +sealing)

Hybrid boltsfriction

anchorage +sealing)

"Cone Bolt®" * type bolts

Self-drilling bolts Friction bolts

Glass fiberbolts

Carbon bolts

Mortar sealing

Resin sealing

Type "MinovaSDA®"

"Alwag" type ATPower®

Type "Swellex®"

Type "Split Set®"

Traction +++ ++++ ++++ ++++ +++ ++ +++ ++ +++ +++ ++ ++

Shear + ++++ +++ +++ ++ ++++ +++ ++ ++ +++ ++ ++

Fractured ground ++ ++ + ++ +++ +++ ++++ +++ ++ ++ ++ ++

Mediocre grounddrillability

o + + o o + ++++ ++++ + o + +

Permanent character

+ ++++ +++ ++++ +++ ++++ +++ o ++ ++ + ++

Immediate action ++++ o +++ ++++ ++++ +++ ++ ++++ ++++ ++++ +++ +++

Delayed action ++ +++ ++++ +++ +++ ++++ ++ +++ +++ +++ +++

Nuisance caused bythe presence of

water++++ + +++ R ++ ++ ++ + ++++ ++++ +++ ++ R ++ R

Water drainage ++++ ++ + ++ + ++ ++ +++ ++ ++++ ++ ++

Waterproofing o ++ +++ R ++ ++ ++ ++ o + + ++ ++

Installation time ++++ ++ +++ +++ ++ +++ +++ ++++ ++++ +++ +++

Legend

++++ Recommended

+++ Good

++ Average

+ Acceptable

o Not recommended

To be checked

Traction: Ability to retain or carry: also depends on the bolt's mechanical characteristics

Shear: Resistance to side movements: also depends on the bolt's mechanical characteristics

Fractured ground: Ground with low RQD: risk of jamming

Action: Immediate or delayed action

Water: Drilling flow

Need for waterproofing or drainage

R: Aqua-reactive resin t

* "Sliding" bolt that, after a slide, retains its efficiency

This table is provided to simplify the choice of bolts. It does not include the cost of supplies or accessories.


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