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Prepared by ERSİN DİK

HACETTEPE UNIVERSITY

Department of Mining Engineering

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Contents:

-Introduction

-Cable Bolt Background

-Bond Strenght

-Grouts and Grouting

-Cable Installation

-Advantages of the Cablebolts

-Cables For Slope Reinforcement-Conclusion

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Introduction

Cable Bolts are

commonly used for rock

reinforcement in areas ofstrata movement.

They can be used to

supplement existingstrata reinforcement.

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Cable Bolt Background 

Cable Bolts have been used

extensively in underground mines

since the early 1970's.

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 At that time, modified cable bolts was

developed to improve the load transfer and was

introduced into both Underground and Open pitMines.

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Summary of the development of cable reinforcing systems for underground mining.

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Cable installation

There are two types of grouting

cables in upholes.

First one is the traditionalmethod of grouting. This method

will be called the ‘breather tube

method’ .( water/cement ratio ˃ 0.4)

 An alternative method, called the ‘grout tube

method’ . (0.3 to 0.35 water/cement ratio).

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  HACETTEPE UNIVERSITYDepartment of Mining Engineering 

Cable installation

Alternative methods for grouting cables in upholes.

Breather tube method Grout tube method

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  HACETTEPE UNIVERSITYDepartment of Mining Engineering 

Cable installation

The main problem with

breather tube method is that

it is difficult to detect when the

hole is full of grout.

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  HACETTEPE UNIVERSITYDepartment of Mining Engineering 

Cable installation

• The principal advantage

of grout tube method is that it

is fair when the hole is full of grout,

• And the smaller number of

components required,

makes the method attractive when compared with the

traditional method.

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Grouts and Grouting

The question of grout quality has always been a

matter of concern in reinforcement systems for

underground construction.

One of the critical factors in this matter has

been the evolution of grout pumps capable of pumping

grouts with a low enough water/cement ratio (by

weight) to achieve adequate strengths.

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Grouts and Grouting

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Grouts and Grouting

Mohr failure envelopes for the peak strength of grouts with different water/cement ratios, tested at 28days.

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Water /cement ratio of 0.35 to 0.4 are significantly

better than those with ratios in excess of 0.5.

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Bond strength

 As the cable pulls out of the grout, the grout

imprints or flutes causes radial displacement or

dilation of the interface between the grout and the

cable.

The radial dilation induces a confining

pressure.It is proportional to the stiffness of the grout

and the rock surrounding the borehole.

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Bond strength

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Forces and displacements associated with a stressed cable grouted into a borehole in rock.

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Cables for slope reinforcement

Drilling machine for the installation of 40 m long reinforcing

cables in 150 mm diameter holes in a dam excavation.

 Also, it may also be

necessary to reinforce

slopes and foundations andcables have proved to be

very effective in suchapplications. 

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40 m long multi-strand cables with a

capacity of 200 tons each being prepared for

installation in a dam excavation.

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Cables for slope reinforcement

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These cables were

installed to stabilise the

slopes of a dam

foundation in gneiss.

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Advantages of the Cable Bolts

Cable bolts also have advantages over other rock

anchors and these include:

• More “stretch” 

• More load capacity

• Higher shear strength 

• The cable’s inherent flexibility 

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Conclusion:

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Clearly cable bolts are generally

a more costly type of rock bolt

support and hence should only be

used where appropriate from a roof

control (safety) point of view.

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