Tunnel Construction in PirPanjal(Himalaya) using NATM, Case
Study T-74R
1) INTRODUCTION1.1Project Description 1.2 Salient features 1.3
Geotechnical risk report2) NATM 2.1 Introduction 2.2 Seven
important features of NATM 2.3 Broad Principles of NATM 2.4
Description of NATM 2.5 Suitability of NATM over TBM 2.6 Components
and sequence of execution in NATM
3) GEOTECHICAL AND GEOLOGICAL INVESTIGATION OF T-74R 3.1
Introduction 3.2 Methodology of field work/ Borehole Drilling 3.3
Regional geology 3.4 Geology along tunnel alignment 3.5 Subsurface
exploration by Drill holes 3.6 Engineering Classification of Rock
Mass 3.7 Geotechnical discussion
4) Tunnel monitoring 4.1 Introduction 4.2 Pressure cell data and
graphs 4.3 Strain meter data and graphs 4.4 Deformation Monitoring
point 4.5 Multipoint Extensometer
5) Conclusion6) Photo Gallery
CHAPTER 01INTRODUCTION
PROJECT DESCRIPTION: Scarcity of land is leading us to find new
innovative construction methods such as underground structures as
lot of congestion is taking place nowadays. As the growth of the
cities continues, abundant infrastructures will be needed and it
raises enormous demand for underground structures. Sustainability
is not possible without the infrastructure and that, often, the
best form of infrastructure involves the underground, and
underground structure must be accelerated with safety and quality
in order to provide the abundant infrastructure required for
development. At present underground structures especially tunneling
have become very important aspect of CIVIL ENGINEERING in vast
variety of fields. With the advancement of technology new tunneling
method including mechanization of various activities involved in
tunneling have been evolved. NATM has been developed in Austria
from where it has got its name. This method makes use of providing
flexible primary lining of shotcrete, wire mesh, rock bolts and
lattice girder. In case of a weaker rock mass the use of pipe for
pole/pipe roofing is also used for crown support which in turn
leads to less over break as well as ensure safety during the
execution of actual work. The main aspect of approach is the
dynamic design based on rock mass classification as well as the
in-situ deformations observed, hence more economical use of the
tunnel support system along the rational approach of execution.With
a view to provide a more reliable and alternative transport system
to Jammu & Kashmir, government of India planned a 345Km long
Railway line connecting the Kashmir with rest of Indian Railway
network. The project has been declared as a project of National
importance.The alignment of this Railway line runs through young
Himalayas, tectonic thrusts and the faults. The length from
Udhampur to Baramulla is 292Km and has been divided into three
sections, details of which are as under: Table: 1.1 The details of
three sections of USBRL
project.Items(Section1)Udhampur-Katra(Section2)Katra-Quazigund(Section3)Quazigund-BaramulaTotal
Length(km)25148 119292
Important/major bridges992 64165
Minor bridges2927 640696
Tunnel length(km) 10.9109.54 --------120.44
No. of stations 312 15 30
Leg-1: Udhampur-Katra(25 km)Executing Agency: Northern
RailwayUdhampur-Katra section is 25 km long and involves 11 km of
tunneling, 9 important/major bridges,29 minor bridges and 10
ROB/RUBs in addition to about 38.86 lac cum of earthwork. The
approx. cost of this stretch is Rs. 640 crores. The tallest bridge
in this section is 90 meter high(br no 20) and the longest tunnel
is 3.15 km long. All the tunneling as well as bridge works have
been completed. However, problem of squeezing and swelling was
faced in tunnel (T-1) due to expansive soil conditions, after
completion of tunnel boring work. To tackle this problem, Railway
has engaged the services of M/s RITES-geo consult (a joint venture
between M/s RITES and M/s geo consult, an internationally renowned
tunnel consultancy firm based in Austria). The consultant has given
the revised scheme of construction of a new diversion tunnel. This
tender for construction of diversion tunnel has been opened on
10.9.2009 and is under finalization. The target for this leg has
been revised to December, 2011.Leg-2: katra-quazigund(148 km)This
leg is the toughest section, full of tunnels and bridges/viaducts
that has been constructed on the Indian railways. The terrain in
this region is full of poor geology and faults .tunneling and
bridging is a challenge greater than that was met on Jammu-Udhampur
or Udhampur-katra section and will be a matter of pride for the
engineers of Indian railways.The stretch between river Chenab and
Banihal is passing through a virgin territory and requires
construction of about 262 km of access roads. About 145 km of
access roads have already been constructed(T-80, pirpanjal
tunnel).this tunnel is 10.96 km long and pierces through the
Pirpanjal range below the snow line. This work on katraQuazigund
section was started in november 2002 and the present progress is
about 13 percent. The engineers working on this section are facing
multifarious problems due to extremely difficult and inaccessible
terrain and technical problems. This project is perhaps the most
difficult new railway line project undertaken on Indian
subcontinent. The terrain passes through young Himalayas, which are
full geological surprises and numerous problems. The execution of
the work has been divided among three agencies as under-1. Northern
railway for first 5 kms2. KRCL for next 71 kms3. IRCON for next 73
kms
The progress of works from km 30 to km 144 has been very slow
due to many failures in
tunnels/tunnel portals. In view of the difficulties being faced
due to adverse geology in the region, Railway board conveyed their
decision to review the alignment from Katra to Banihal. On Railway
boards directions, M/s IRCON appointed an International Consultant
(M/s Amber Engineering Ltd., Switzerland) for the purpose of
studying the alignment.
1.2 SALIENT FEATURES:Table 1.2: The project has many special and
unique features and several first in Indian Railways.
ItemUdhampur-KatraKatra-QuazigundQuazigund-Baramulla
Max.Curvature(degree)2.752.752.75
Maximum height of bridge(m)85m359m13
Longest span(m)154m steel girder over the river Jhajjar465m
steel arch over the river Chenab45m
Longest tunnel(km)3.1511.21-------
Max. depth of bank(m)21559.7
Max. depth of cutting(m)204012
Alignment on curvature14%37.83%14.66%
The project is one of the most difficult projects under taken on
Indian subcontinent. The terrain passes through young Himalayas,
which are full of geological surprise and numerous problems. For
execution purpose, project has been divided into three
sub-sections. Construction progress is on its way. Katra Quazigund
leg is most difficult stretch of this project. The alignment of
this stretch which is 148Km long passes through Patni and PirPanjal
ranges.This alignment requires construction of 92
important/measures bridges and 27 minor bridges, the alignment also
requires, interlaid construction of 65 number of tunnels, totaling
to a length of 110Kms bringing the percentage of the total length
of the alignment on tunnel to approx. 76%.
1.3 Geotechnical risk report (T 74 R)
The main objectives of the geotechnical risk comprise the
identification, description and assessment of the geological and
geotechnical risk associated with ground conditions that strongly
influence the relevant structure of the project and the
construction process. It also includes the geological
characteristics of the project area.
Data basis used for the analysis1. Geological and remote sensing
by geological survey of India.2. Geological map (1:25000)3.
Geomorphological map (1:25000)4. Tectonic map (1:25000)5. Drainage
map (1:25000)6. Geological report
Methodology for the geotechnical analysis focusing on the risk
assessment:1. Preconstruction survey from katra-Quazigund new BG
rail line project(phase 1 and 2), km 30-km 168 for the basis for
the geotechnical and geological risk study and this analysis is
carried according to following general procedure:
a> Investigation of geological conditions which includes
study of geological maps, site visits etc.b> Geological
characterization of the project areac> Establishment of
characteristic ground type which is representative of whole project
area.d> Allocation of the ground type to the alignmente>
Identification of general geotechnical hazards and definition of
geotechnical key parameters relevant for each particular
hazard.f> Allocation of geotechnical hazard to the
alignmentg> Definition of different types of construction
measures for tunnel, tunnel portals, open cuts, embankments and
bridges.h> Identification and quantification of the risk of
occurrence of unexpected faults, ground water conditions and
landslides.i> Influence of construction measures on geological
conditions.
CHAPTER 02NATM
IntroductionNATM was first described as the modern tunneling
method by Rabcewick. This method was developed in Austria from
where it got its name. This method makes use of primary flexible
lining of shotcrete, wire mesh, lattice girders, rock bolts. In
case of weaker rock mass the use of pipe fore pole/pipe roofing is
also used for crown support which leads to less outbreak and
ensures safety during the execution of the actual work. The main
aspect of NATM is the dynamic design based on the rock mass
classification as well as in-situ deformations observed, hence more
economical approach towards the design along with the rational
approach of execution.
The New Austrian Tunneling Method includes a number of
techniques for safe tunneling in rock conditions in which the
stand-up time is limited before failure occurs. These techniques
include the insect: smaller headings and benching or the use of
multiple drifts to form a reinforced ring made which the bulk of
the tunnel can be excavated. These techniques are applicable in
soft rocks such as shales, phyllite and mudstones in which the
squeezing and swelling problems are likely to occur. The techniques
are also applicable when tunneling in excessively broken rock, but
great care should be taken in attempting to apply these techniques
to excavations in hard rocks in which different failure mechanisms
occur.
The NATM is rather a concept or philosophy than a construction
method, where the surrounding soil - or rock mass of a tunnel is
integrated into the overall support structure, the rock is
activated to a load bearing ring around the tunnel. Old
conventional tunneling methods considered the rock mass surrounding
the tunnel only as a loading member.
In NATM the initial tunnel support consisting of shotcrete,
reinforced by wire mesh or steel fiber, possibly steel ribs and
rock bolts, is installed in close contact with the rock surface to
form a composite structure. The composite system rock
(soil)/supporting elements allows the control of deformations to
achieve stress release and stress redistribution around the tunnel.
It also limits the loss of natural rock/soil strength in order to
maintain the carrying capacity of the rock arch around the
tunnel.During construction continuous geotechnical measurements and
controls are carried out to monitor the stress re-arrangement
process, to control stability and to optimize the supporting
system, construction sequence and to verify the rock
classification. NATM represents the state of the art in modern
tunneling. Its concept makes NATM more economical than conventional
means of tunneling.
Seven Important Features of NATM 1. Mobilization of the strength
of the rock mass.2. Shotcrete protection3. Measurement4. Lining5.
Closing of invert6. Rock mass classification7. Dynamic design.
BROAD PRINCIPLES OF NATM NATM is broadly based on following
principles:Mobilization of the strength of the rock mass: the
method relies on the inherent strength of rock mass being conserved
as the main component of tunnel support. Primary support is
directed to enable the rock to support itself. Shotcrete
protection: loosening and excessive rock mass deformation should be
by filling a layer of 25-50mm of sealing shotcrete immediately
after opening of the face.Measurements: Every deformation of the
excavation must be measured. NATM requires installation of
sophisticated instruments. These are embedded in lining, ground
such as load cells, extensometers and reflectors. Primary lining:
The Primary lining is thin. It is active support and the tunnel is
strengthened not by thicker lining, but by flexible combination of
rock bolts, wire mesh and lattice girders.
Closing of invert:- Early as far as possible closing the invert
so as to complete the arch action and creating a load bearing ring
is important.it is crucial in soft ground conditions.Rock mass
classification: - The participation of the expert geologist is very
important as the primary support as well as the further designing
of the support, etc.during the excavation of the rock requires
classification of the rock mass.Dynamic design: - The designing is
dynamic during the tunnel construction .Every face opening
classification of rock is done and the support are selected
accordingly. Also the design is further reinforced based on the
deformation as noticed during the monitoring.Lauffer(1958) proposed
that the standup time for an unsupported span is related to the
quality of the rock mass in which the span is excavated.in a
tunnel, the unsupported span is defined as the span of the tunnel
or the distance between the face and the nearest support, if this
is greater than the tunnel span. Lauffers original classification
has since been modified by a number of authors, notably pacher at
al (1974), and now forms part of the general tunneling approach
known as the New Austrian tunneling method.The significance of the
standup time concept is that an increase in the span of the tunnel
leads to a significant reduction in the time available for the
installation of support. For example, a small pilot tunnel may be
successfully constructed with minimal support, while a larger span
tunnel in the same rock mass may not be stable without the
immediate installation of substantial support.The new Austrian
tunneling method includes a number of techniques for safe tunneling
in rock conditions in which the standup time is limited before
failure occurs. These techniques include the use of smaller
headings and benching or the use of multiple drifts to form a
reinforced ring inside which the bulk of the tunnel can be
excavated. These techniques include the use of smaller headings and
benching or the use of multiple drifts to form a reinforced ring
inside which the bulk of the tunnel can be excavated. These
techniques are applicable in soft rocks such as shales,phyllite and
mudstones in which the squeezing and swelling problems, described
by Terzaghi (discussed in next coming chapter), are likely to
occur. The techniques are also applicable when tunneling in
excessively broken rock, but great care should be taken in
attempting to apply these techniques to excavations in hard rocks
in which different failure mechanisms occur.In designing support
for hard rock excavations it is prudent to assume that the
stability of the rock mass surrounding the excavation is not time
dependent. Hence, if a structurally defined wedge is exposed in the
roof of an excavation, it will fall as soon as the rock supporting
is removed. This can occur at the time of the blast or during the
subsequent scaling operation. If it is required to keep such a
wedge in place, or to enhance the margin of safety, it is essential
that the support be installed as early as possible, preferably
before the rock supporting the full wedge is removed. On the other
hand, in a highly stressed rock, failure will generally be induced
by some change in the stress field surrounding the excavation. The
failure may occur gradually and manifest itself as spalling or
slabbing or it may occur suddenly in the form of a rock burst. In
either case, the support design must take into account the change
in the stress field rather than the stand up time of the
excavation.
2.4 Description of T-74 RThe tunnel T-74R extends between
chainage 124,200km at south portal to chainage 132.840km at north
portal having a shaft and an adit.The total length of this tunnel
is 8.64km from portal to portal. The estimated project cost is 800
crores INR.Fault lines in case of young Himalaya are the main
challenge for tunnel construction in pirpanjalrange. The tunnel
consists of a main tunnel and an escape tunnel which are connected
by CPBs at suitable intervals making a total of 7 CPBs in the total
tunnel length. The length of escape tunnel is shorter than main
tunnel. Escape tunnel is provided for emergencies which may happen
during traffic operations.The center to center distance between
main tunnel and escape tunnel is 20-30 km .During the construction
of t-74R, sump well and pumping system of drainage has been used
.Two air ducts were provided for defuming and ventilation purpose.
The main method of excavation was drill and blast, however heading
and benching was adopted at places.
2.5 Suitability of NATM over TBM1.TBM design requires reliable
geological information in the initial stage itself and there is
always likelihood of mixed-face excavation in PirPanjal.2.There is
also heterogeneous geology in soil near portals to trap and
quartzite in middle which is not well suited for TBM.3.Heavily
faulted areas and/or wide fault ones are also expected, TBM may be
trapped by ground movement behind the face.4. High squeezing is
anticipated in the middle zone with 1150 overburden and likelihood
of heavy water inflow in the limestone zone with heavy
overburden.5.Retrieval of TBMs approaching each other requires
large cavern.6.TBM obstructs final lining for a long time.7.Non
circular sections cant be achieved after enlargement later.8.TBM
requires specialized skilled crew and also there is heavy
requirement of electric power.
Because of all these reasons NATM was selected for tunneling in
PirPanjal instead of TBM.
2.6 Components and sequence of execution in NATMThe various
steps of execution of tunneling in NATM are as follows:1. Face
drilling2. Loading/charging and blasting3. Defuming4. Mucking5.
Profiling(by total station06. Shotcreting7. Erecting lattice
girders.8. Rock bolting
Face drilling includes the drilling of holes for the gelatin
explosive horizontally in the face of tunnel at every section to be
blasted. The holes are usually drilled in the of 25mm,32mm or 40mm
diameter , dependingon the diameter of explosive pallet/rod to be
used. Only a few of the holes drilled in the tunnel face are
actually charged with explosive, rest of them are left as dummy
holes which is very important to maintain the profile of tunnel
section and avoid irregular cutting, over break and undercutting as
much as possible.Charging is the second step of tunneling after
drilling holes. It involves loading the particular holes with
gelatin explosive. After covering the face with some fiber to
prevent scattering out of the stone pallets which may cause hazard,
the charge is detonated by different methods which may be electric
detonator or it can be NED(non electric detonator).Defumingmeans
removal of dust from the dig out tunnel which is generated by the
blasting of rock. Defuming is done with the help of ventilators
already installed in the tunnel usually for one hour. Defuming is
necessary to maintain the working condition inside the tunnel as
fresh air,visibility,etc.Mucking involves the removal of large
amount of broken rock materials which is formed blasting and
dumping the same into muck yard. Large no of loaders, excavators,
trucks and dumpers are used to assist the process. After mucking is
complete, chipping and filling of overcut is done. For chipping
boomer, and rock breaker is used, overcuts are filled by shotcrete.
After this step is complete, profiling using total station is again
done on the new face exposed.Shotcreting A primary layer of
shotcrete is applied immediately after the mucking is complete. Its
thickness is usually 50mm and it consists of M20 concrete
reinforced with steel fiber(SFRC). Primary shotcrete is very
important for stability of loosened rock caused by the blast due to
drilling and blasting and to form a uniform lining of
tunnel.Erection of lattice girders and rock bolting : In case of
weak rock classes the standup time is less and self-supporting
property is lacking , hence lattice girders are necessarily
installed/erected to support the rock mass. The frequency of
lattice girders depends on rock class as well. For class 5 usually
heavy steel girders with a spacing not greater than 0.9m is used.
While as for class 4 lattice girders spaced not greater 1.5m apart
were used. In case of rock class 4 fore polling is also needed,Rock
bolting is one of the unique and important features of NATM. Rock
bolts are used to anchor different strata of rock together to
prevent rock from collapse. The plastic region generated by
blasting operation is anchored to the stable rock sections at
deeper levels.Different types of bolts and nails are driven into
the side walls and crown of the tunnel as per design and
requirement which is governed by the geological condition of the
tunnel.The different types of rock bolts used in tunnel 74-R are
discussed below:
1. SN Rock Bolt:Soil nail rock bolt are 4-5m long Fe-415 bolts
of diameter 25mm-32mm used in tunnel rock bolting commonly. It is
simply nailed into the tunnel wall with the help of boomer. These
are cheaper than other types of rock bolts.
2. Swellex Rock Bolts:These rock bolts are used at places where
too much water comes out of tunnel wall. This type of bolts is
swelled once it is inserted into the wall with the help of a water
jet at high pressure. Diameter varies from 25-32mm, and length
varies from 4-6m.
3. SDA/SDR Bolt:Self-Drilled Anchor comes with a tungsten
carbide alloy bit at its tip which helps to drill in this bolt into
the tunnel wall. SDA is used at places where Sn bolts cant be
driven due to crushed rock mass and collapse of drilled holes.
Diameter of SDA 25mm to 76mm and length ranges from 4-6m.
CHAPTER 03GEOTECHNICAL AND GEOLOGICAL INVESTIGATION OF T-74R
3.1 IntroductionThis chapter includes results of shallow and
deep boreholes, geological logs, and laboratory test results of
representative rock core/samples, standard penetration test (SPT)
besides geological studies around the tunnel T-74 alignment
area.
Objective and scope of work:The objective of the investigation
for tunnel T-74R is to generate a report incorporating subsurface
geological data collected from different boreholes together with
limited surface geological studies carried out along the tunnel
alignment.
Another important objective was to prepare geological logs of
the completed boreholes and to prepare geological sections along
the tunnel alignment for future reference and records.
3.2 Methodology of field work:
BOREHOLE:In total 9 numbers of boreholes, 4 deep and 5 shallow
have been drilled along the tunnel alignment area. Most of these
boreholes have been drilled upslope of the alignment and projected
on the actual tunnel alignment for interpretation and preparation
of geological section. Layout plan of drill holes is attached as
fig 3.1 in this report. The summary of boreholes with depth and
location is given in table 3.1.
BOREHOLE DRILLING:
Wire-line rigs which are hydraulic operated are used. Drilling
is carried as per IS 1892 -1979.
Equipment:Following equipment were used for the execution of the
work:1. Drill rig with accessories and mud circulation pump.2.
Casing of required size.3. NX size core barrel.
Table 3.1: The summary of boreholes with depth and
locationSr.No.Borehole
No.Elevation(m)CoordinatesChainage(Km)Formation level (invert)
(m)Depth(m)
111867.525N3695043.383E512930.391125.7901564.097315.00
221989.339N3694573.992E515062.361128.3821593.968415.00
331915.916N3694397.190E515402.385128.7591598.58262.00
442112.570N3694179.892E515732.904129.1531603.317520.00
55A1692.707N3694957.932E517665.796132.4601642.45060.20
65B1677.039N3694992.593E517711.077132.4961642.07545.10
761712.743N3695576.809E517796.357133.0181648.85636.00
86A1712.473N3695578.950E517796.388133.0311649.70385.20
971723.913N3695576.950E517796.388133.0891649.70385.20
Field Execution:Wire-line rig is used for drilling. The diameter
of the borehole in soil was 100/150mm. Casing was used to protect
the bore hole from the side collapse. Initially guide casing is
provided and further boring was carried out of 100/150mm dia. size
in soil. SPT, DS I conducted as per specification or as per
direction of engineer in charge. Whenever rock is encountered,
NX/NQ core barrel is used to collect the rock samples. The SPT, DS
and rock sample are preserved into core boxes with labels. Rotary
drilling machines uses a rotary action combined with downward force
to grind away the material in which a hole is being drilled. Rotary
drilling machine requires a combination of a number of elements1. A
drilling machine or a rotary drill at the ground surface which
delivers torque and thrust.2. A flush pump, which pumps the fluid
down the hole in order to cool the mechanical parts and lift the
cutting of the rock to the ground surface as drilling proceeds.3. A
string of hollow drill rods, which transmit torque from the rig and
flush the fluid from the flush pump to the bottom of the hole4. And
a drilling tool for example core barrel which grinds away the rock
and in addition may be designed to take a sample.
Fig 3.2 wire line rotary core drillingWire line drilling is a
technique which has been used widely for deep drilling for many
years, principally because it reduces the trip time (i.e. time
required to extract the core tube from the bottom of the hole,
empty the core and replace the core tube). This technique has
proved to be very effective in coring of the relatively difficult
deposits such as over consolidated clays, chalks and interlayer
sands, gravel, limestone and clays.
In conventional drilling the outer barrel is connected to a
smaller diameter strings of rods, which in turn is passed through
the chuck of drilling rig. Each time the core barrel is withdrawn,
the entire string of rods must be withdrawn and dissembled, after
the core is recovered the whole rod must be reassembled, trip time
increases linearly with the depth. In unstable ground outer casing
must also be used.Wire line drilling does not use any outer casing,
but instead uses an outer barrel which extends at full diameter to
ground level. The inner barrel is lowered through the full length
of the outer barrel on a wire line. When it reaches the bottom of
the hole it latches inside the outer barrel in the correct vertical
position. The outer barrel s turned by the rig, as flush is pumped
down it. The latching mechanism holds the inner barrel down but
does not fix it so that it must rotate with the outer barrel. When
the outer and inner barrels have been drilled for the length of the
run, the wire line is winched upwards. The inner barrel and the
core are hoisted to ground surface, where the core is extracted
band a new length of outer barrel is added to the string.
Standard Penetration Test (SPT):SPTs are conducted as per Indian
Standard (IS 2131-1981). In SPT test a slit spoon sampler is driven
at the bottom of the borehole. The penetration resistance in terms
of blow of 300mm penetration of the split soon sampler is measured
as N value. The blows are imparted by a standard weight of 63.5kg
falling through a height of 750mm. The resistance of first 150mm is
ignored since those blows are considered as seating blows due to
loosening of the strata. The resistance of next 300mm of
penetration value N, if the sampler is driven less than 450mm, then
the penetration resistance is given for at least 300mm of
penetration. If the penetration depth is less than 300mm and the
blow count is more than 100 then N value is considered as refusal
and actual penetration is recorded with the blows given.SPTs have
been conducted in the drill holes along the alignment of T-74R.
Though empirical in nature, its a practicable method of determine
safe bearing capacity of the soil. Drilling through hard
strata/rock:The hard stratum is confirmed either by refusal from
SPT test or due to resistance during drilling operation. Once the
hard stratum is net with it, further drilling is carried by NX core
drilling with TC/Diamond bits using double core barrel. Triple tube
core was used whenever core recovery is considerably reduced. The
work is done as per IS: 6935-1973. Each run of the core drilling is
properly recorded. The cores are carefully transferred to the core
boxes and preserved. The core recovery percentage is recorded and
also the core pieces transferred to theCore box are numbered and
properly labeled. Rock Quality Designation is also recorded. Some
of the core samples are sent to the laboratories for conducting
tests.
Rock Core Recovery {C.R %= (cumulative length of cores/Length of
run) x 100} and Rock Quality Designation (RQD), RQD= (total length
of core pieces of>10cm and above in length/length of run) x
100.
"RQD = (Sumof10)/Itot * 100%"Where (Sumof10) = Sum of length of
core sticks longer than 10 cmItot = Total length of core run
3.3 Regional GeologyThe Katra-Quazigund railway line passes
through geology from rocks of Siwalik and Murree group of foreland
to pre-tertiary rocks of lesser Himalayas. These rocks are
traversed by number of thrusts and faults which are still
considered to be an active. Due to this tectonic activity the rocks
along the proposed alignment are highly jointed, fractured and
folded. The trend of the rock is NW-SE having dip toward NE
direction. Murree thrust marks the tectonic contact between
tertiary and pre-tertiary rocks. Its considered to be an
autochthonous folded belt of tightly compressed, recumbent
anticline. It lies between the Muree group of foreland and the
SalkhalaMetasediments of the Kashmir nape. Its outer boundary is
marked by Murree thrust, which has brought rock of this par
autochthonous belt over the Murree group. The northern boundary is
marked by Panjal thrust, which has brought the entire Himalayan
Phenorozois succession of Kashmir over the lesser Himalayan
belt.
The rocks of par autochthonous belt are tectonically overlaid by
Salkhala group of rocks along PirPanjal thrust. The Salkhala group
consists of thick sequence of schistone quartzite, phyllite and
schist intruded by Granodiorite, gabbro, pegmatite and basic rocks
along Panjal thrust. These are unconformably overlain by Ramsu
formation comprising of highly compressed sequence of phyllite,
carbonaceous slates, quartzite and limestone which are overlaid by
rocks of Machal formation comprising phyllite, quartzite, slate,
agglomerate tuff and limestone. Machal formation is unconformably
overlaid by limestone, marl quartzite, slate lithology of
Syringotheris limestone formation. These are overlaid by fenestella
shale, agglomerate slate and Panjal volcanic formation exposed in
the Banihal tunnel. Towards north of Banihal tunnel, The folded
Triassic limestone along with minor Jurassic shale beds are exposed
in the section uptoQuazigund. Quaternary sediments represented by
karewas formation are exposed beyond Quazigund toward north upto
Srinagar in Kashmir.
Table 3.1: Stratigraphic sequence(Based on GSI special
publication 26, 1998)
FormationLithographyAge
Quaternary SedimentsSoil, clay, sand, pebbles
etc.-------------
KarewasClay, silt, sandPliocene and Pleistocene
SiwalikSandstone, clay, stone, siltstone and conglomerateMiocene
and Pleistocene
----------Main boundary fault-----------------
MurreeSandstone, clay, stone, siltstoneMiocene to Oligocene
-------------Murree thrust---------------
VihiLimestone and shaleTriassic to Jurassic
ZewanLimestone, slate and flagstoneMiocene to Oligocene
Panjal volcanicBasic lava flowPermian
Agglomerate slateSlate with pyroclasticsUpper carbonaceous
Fenestella shaleQuartzite, slate, basic silt, shaleMiddle
carbonaceous
SyringotherisLimestoneMachalSilicified limestone, limestone
phyllite, slate, agglomerate tuff and limestoneLower carbonaceous
CambroSilurian
RamsuPhyllite, carbonaceous, phyllite/slate, quartzite and
limestoneCarbo-silurian
RambanPhyllite, slate, quartzite, gypsumProterozoic
-----------------------------------------------Panjal
Thrust---------------------------------------------------------
SalkhalaSlate, phyllite, carbonaceous phyllite, quartezite,
marble with gypsum bandsProterozoic
3.4 Geology along the Tunnel Alignment:Ramsu formation
comprising phyllite, carbonaceous phyllite/slates, quartzite and
limestone are exposed along major part of the tunnel alignment
having faulted contact with the overlying Machal formation
consisting of phyllite, slate, quartzite, agglomerate tuff and
limestone towards T-74P2. Towards south of the alignment rocks
belonging to Sarkanthgranitite comprising granite, Granodiorite and
dumgali formation comprising quartzite, and phyllite are exposed.
Towards further north of T-74P2 syringotheris Limestone represented
by limestone, marl quartzite, slate lithology is exposed. The rocks
are highly fragile, thinly foliated and fractured.Identification of
ground types and allocation to the alignment:General ground types
of characteristics for the corresponding geological formation are
deduced from geological investigation.Table 3.2: General geological
information along alignment FormationLithological unitAbstract
TrikutaDolomite, dolomitic limestoneGenerally brittle rock,
medium to highly fractured
Fault zonesSeveral hundred meter thick brittle fault zones
Reasi thrustDolomiteCompletely fractured
Quartzite
Intermediate layers of shale
Fault zonesSmall width, brittle fault zones
Geomorphology and Ground Condition:The area around the proposed
tunnel alignment forms rugged topography having high hills and deep
valleys formed by drainage system mainly controlled by EW flowing
Mohmangat Nala and NS flowing Bichlari Nala ad their tributaries.
The area was studied on the basis of Google earth and limited
traverse studies and prepared a map.
SEISMIC ZONATION MAP OF THE INDIA:
Local geology of the tunnel:Major part of the tunnel alignment
is occupied but Ramsu formation comprising phyllite, carbonaceous
slate, quartzite and limestone from 125.300km to 133.000km and from
133.00km to 133.900km (T-74P2), Machal formation comprising
phyllite, slate, and agglomerate tuff and limestone are exposed.
The rocks are highly fragile, thinly foliated and fractured in
nature. Weathering grade of the rock is between W/I to W/IV. The
tunnel alignment area is covered by hill wash and debris material.
The area all along the alignment is slide prone. The general trend
of rock mass varies from N700W-S700E to N300W-S300E with dip 400 to
700 north easterly. Wide variation in dip and strike indicates that
the rock have undergone intense deformation due to folding and
faulting. Generalized geological map of the area has been prepared
(after AMBERG) and using borehole data with limited traverse
studies.
Fault: The proposed tunnel may intercept faulted contact between
Ramsu formation and Machal formation around chainage 132.650km at
tunnel formation level. Heavy ingress of water together with the
abnormal over break is expected in this section.
Fold:The anticline fold is suspected roughly along the Mohmangat
Nala. This is indicated by variabledip of rocks along both the
banks of Nala, however this fold is located from the tunnel
alignment.3.5 Subsurface Exploration by Drill Holes:BH-01: Drilled
at chainage of 125.790km reveks 69m thick overburden. From 0.00m to
20m, over burden consists of hill slope debris material consisting
of highly weathered fragments/rock cutting of quartz, phyllite
intermixed with greyish brown silt clay matrix and from 20m to 69m
overburden consists of light greyish to whitish color rock
fragments of phyllite with iron oxide leaching and wash material.
The overburden appears to be an old slide zone. From 69m-124m depth
the bedrock consist of fine grained, light grey to grey colored,
highly fractured phyllite with 600 to 650 foilation. Quartz veins
and limonitic staining is seen at places. From depth 124m-145m
depth, phyllite and quartzite are recorded. Phyllite is light grey
to grey in color, the rock is highly fractured from 145m-227m,
greyish to dark greyish in color, inclined jointed, highly
fractured and foliated quartzite phyllite is recorded. Light grey
to grey colored,
fine grained, moderately weathered and fractured phyllite is
noticed from 227m-263m, again from 263m-269m depth, dark grey,fine
to medium grained, moderately weathered and strong quartzite
phyllite has been encountered .From 269m-280m , grey to dark
grey,fine grained, foliated, highly fractured and weathered , weak
phyllite with quartz vein along foliation plain is see. From
280m-315m, grey to dark grey colored, quartzitephyllite with quartz
veins has been recovered. Core recovery varies from nil to 100% RQD
is nil to 67%.Overall quality of the tunnel media is poor. At
formation level,RL 1564.097m highly fractured and foliated
quartzite phyllite is present. Average RQD at the formation is
18%.BH-2: drilled at chainage 128.382km revealed overburden
consisting of weathered fragments of quartz and phyllite in clay
silty matrix upto 18.50 depth. The overburden material indicates
presence of slide zone or debris flow material. From 18.5 to 53.00,
bedrock consists of grey colored, fine grained, weathered and weak
phyllite with iron oxide leaching is rerecorded .From 53.00 to
176.00m, light grey to grey colouredphyllite at places,
quartzitic/schistose in nature, inclined foliation, highly
fractured with 45% to 60% foliation and quartz vein is recorded.
From 282.50 to 318.50 m light grey coloured thinly foliated, weak
phyllite, highly fractured is recovered. From 318.50 to 335.00m,
black coloured fine grained, thinly foliate and
pyritiferousphyllite showing appearances of graphite at places is
recorded. From 335.00m to 350.00m, dark grey to black colored, fine
to medium grained, fractured carbonaceous phyllite/phyllite with
joints 60 degree to 80 degree is noticed and from 350m to 383m
complete water loss, no core recovery or wash material is
recovered. From 383.00m to 402.00m,lightly grey, fine to medium
graine,slightly weathered and fractured, pyritiferousphyllite with
slate/phyllite, quartz veins along foliation planes is noticed and
from 402.00m to 415.00m black, fine to medium grained, moderately
weather, carbonaceous phyllite with black color wash sample from
402.00404.00, 405.00-406.00m and from 408.00m to 415.00m. Core
recovery is nil to 92% and RQD varies from nil to 57%. The overall
quality of the rock mass is poor.BH-3Drilled at chainage128.759km,
the borehole has recovered overburden from 0-21m depth consisted of
fragments of slate and phyllite in dark brownish coloredsilty/clay
matrix. Overburden material indicates old slide zone. From 21-50m
depth bed consists of light to darkgreycolored, fractured
agglomerate slate/phyllite. From 50-62 m depth borehole has
encountered greyish white colored, fine grained, highly fractured
and moderately strong phyllite. Weathering grade varies from W1 to
W2.SPT test conducted at 1.50 to 1.55m recorded refusal to
penetration. Core recovery varies from 14 to 23% and RQD is nil.
The bore hole has not touched the formation level.
Geotechnical laboratory tests:Geotechnical tests of large size
intact core samples have been conducted by geotechnical laboratory
IIT Bombay. The tests conducted are tensile strength test , point
load test ,uniaxial compressive strength test, modulus of
elasticity , poison ratio, dry density and other tests such as
specific gravity, water content etc.Tensile strength ranges from
10.15 kg/cm2 to 118.11 kg/cm2 point load (KN) from 2.80 to
20.25,UCS from 60.80 kg/cm2 to 3712 kg/cm2 , modulus of elasticity
from 0.2331 to 1.587 kg/cm2, poison ratio from 0.0765 to 1.0701 ,
dry density from 2.164 to 2.966 gm/cc and permeability conducted on
soil and rock sample yielded legion values between 0.00 to
44.81.
3.6 Engineering classification of rock mass:During the
preliminary stage, the use of rock mass classification is of
considerable importance in the absence of detailed information
about the orientation of the discontinuities,filling, spacing and
continuity etc. at the formation grade. The main aim and objective
of the rock mass classification is to provide an overall idea about
the rock mass quality likely to meet with at the formation grade,
for engineering design and to prepare for remedial measures, in
advance. In this respect two different rock mass classifications
have been used. These are Q and RMR rating system which are based
on the surface geological studies and data obtained from the drill
holes. Based on the Q and ESR value, recommended maximum
unsupported excavation span and estimated tunnel support system has
been suggested besides average standup time of the rock mass has
also been determined on the basis of RMR class no.
ROCK MASS CLASSIFICATION:Terzaghis rock mass classificationThe
earliest reference to the use of rock mass classification for the
design of tunnel support is in a paper by Terzaghi in which the
rock loads, carried by steel sets, are estimated on the basis of a
descriptive classification. While no useful purpose would be served
by including details of Terzaghis classification .While no useful
purpose would be served by including details of Terzaghis
classification in the discussion on the design of support, it is
interesting to examine the rock mass descriptions included in his
original paper because he draws attention to those characteristics
that dominate rock mass behavior, particularly in situations where
gravity
Constitutes the dominant driving force.The clear and concise
definitions and the practical comments included in these
descriptions are good examples of the type of engineering geology
information, which is most useful for engineering design.
Terzaghis descriptions (quoted directly from his paper) are:1.
Intact rock contains neither joints nor hair cracks. Hence, if it
breaks, it breaks across sound rock. On account of the injury to
the rock due to blasting, spalls may drop off the roof several
hours or days after blasting. This is known as a spalling
condition. Hard, intact rock may also be encountered in the popping
condition involving the spontaneous and violent detachment of rack
slabs from the sides of roof.2. Stratified rock consists of
individual strata with little or no resistance against separation
along the boundaries between the strata. The strata may or may not
be weakened by transverse joints. In such rock the spalling
condition is quite common.3. Moderately jointed rock contains
joints and hair cracks, but the blocks between joints are locally
grown together or so intimately interlocked that vertical walls do
not require lateral support. In rocks of this type, both spalling
and popping conditions may be encountered.4. Blocky and seamy rock
consists of chemically intact rock fragments which are entirely
separated from each other and imperfectly interlocked. In such
rock, vertical walls may require lateral support.5. Crushed but
chemically intact rock has the character of crusher run. If most or
all of the fragments are as small as fine sand grains and no re
cementation has taken place, crushed rock below the water table
exhibits the properties of a water bearing sand.
Rock quality designation index (RQD)The rock quality designation
index (RQD) was developed byDeere (Deere at al 1967) to provide a
quantitative estimate of rock mass quality from drill core logs.RQD
is defined as the percentage of intact core pieces longer than
100mm in the total length of core. The core should be at least NW
size and should be drilled with a double tube core barrel. The
correct procedures for measurement of the length of core pieces and
the calculation of RQD are summarized below in fig.3.4.
Palmstrom (1982) suggested that when no core is available but
discontinuity traces are visible in surface exposures or
exploration results, the RQD may be estimated from the number of
discontinuities per unit volume. The suggested relationship between
clay-free rock masses is:RQD = 115- JvWhere Jv is sum of number of
joints per unit length for all joints (discontinuity) sets known as
the volumetric joint count.RQD is the directionally dependent
parameter and its value may change depending upon the borehole
orientation. The use of volumetric joint count can be useful
reducing this directional dependence.RQD is intended to present the
rock mass quality in situ. When using diamond drill core, care must
be taken to ensure that fractures, which have been caused by the
handing other drilling processes are identified and ignored while
determining he value of RQD.Here blast induced fractures are not
included in the estimation of the Jv
Q System:Large part of the tunnel alignment constitutes entirely
Ramsu formation comprising phyllite, quartzite phyllite, with
subordinate carbonaceous phyllite, quartzite and limestone bands
and Machal formation constituting entirely by phyllite and slates
with rare limestone and agglomerate interbands. Therefore, Q value
and RMR classification has been calculated in respect of phyllite,
quartzite phyllite and slate which are crossing major part of the
tunnel alignment.On the basis of an evaluation of a large number of
case histories of underground excavations, Barton et al (1974) of
the Norwegian Geotechnical Institute proposed a tunneling Quality
Index (Q) for the determination of rock mass characteristics and
tunnel support requirements. The numerical value of the index Q
varies on a logarithmic scale from 0.001 to a maximum of 1,000 and
is defined by:Q= (RQD/Jn) x (Jr/Ja) x (Jw/SRF)Where RQD is the rock
Quality DesignationJn is the joint set numberJr is the joint
roughness numberJa is the joint alteration numberJw is the joint
water reduction factorSRF is the stress reduction factor
In explaining the meaning of the parameters used to determine
the value of Q, Barton et al (1974) offer the following
comments:The first quotient (RQD/Jn), representing the structure of
the rock mass, is a crude measure of the block or particle size,
with the two extreme values (100/0.5 and 10/20) differing by a
factor of 400. If the quotient is interpreted in units of
centimeters, the extreme particle sizes of 200 to 0.5cm are seem to
be crude but fairly realistic approximations. Probably the largest
blocks should be several times this size and the smallest fragments
less than half the size.
The second quotient (Jr/Ja) represents the roughness and
frictional characteristics of the jointwalls or filling materials.
This quotient is weighted in favor of rough, unaltered joints in
direct contact. It is to be expected that such surfaces will be
close to peak strength, that they will dilate
Strongly when sheared, and they will therefore be especially
favorable to tunnel stability.When rock joints have thin clay
mineral coatings and fillings, the strength is reduced
significantly. Nevertheless,rock wall contact after small shear
displacements have occurred may be a very important factor for
preserving the excavation from ultimate failure.Where no rock wall
contact exists, the conditions are extremely unfavorable to tunnel
stability. The friction angles are a little below the residual
strength values for most clays, and are possibly downgraded by the
fact that this clay bands or fillings may tend to consolidate
during shear, atleast if normal consolidation or if softening and
swelling has occurred. The swelling pressure ofmontmorillonite may
also be a factor here.The third quotient (Jw/SRF) consist of two
stress parameters. SRF is a measure of: 1) loosening load in the
case of excavation through shear zones and clay bearing rock, 2)
rock stress in component rock, and 3) squeezing loads in plastic in
competent rock. It can be regarded as the total stress
parameter.The parameter Jw is a measure of water pressure, which
has an adverse effect on the shear strength of joints due to a
reduction in effective normal stress. Watermay, inaddition, because
softening and possible outwash in the case of clay-filled joints.it
has proved impossible to combine these two parameters in terms of
inter-block effective stress, because paradoxically a high value of
effective normal stress may sometimes signify less stable
conditions then a low value, despite the higher shear strength.
Thequotient (Jw/SRF) is a complicated empirical factor describing
the active stress.It appears that the rock tunneling quality Q can
now be considered to be a function of only three parameters which
are crude measures of:1. Blocksize (RQD/Jn)2. Inter-block shear
strength (Jr/Ja)3. Activestress (Jw/SRF)
Geo-mechanics Classification/RMR classificationBieniawski(1972)
published the details of a rock mass classification called the
Geo-mechanics classification or the rock mass rating (RMR) System.
Over the years, this system has been successively refined as more
case records have been examined and the reader should be aware that
bieniawski has made significant changed in the ratings assigned to
different parameters. The discussion which flows is based up on the
1989 version of the classification (Bieniawski, 1989). Both the
version and the 1976 version deal with estimating the strength of
rock masses. The main aim of this classification is to provide
guideline for tunnel support to ensure the stability of various
classes of rock mass. The advantage of this classification is that
it considers the various parameters likely to influence the
engineering behavior of rock. Also the rating of these parameters
is easy to determine at the site itself. Following six parameters
which have been included are:1. Uniaxial compressive strength (UCS)
of intact rock2. RQD3. Spacing of discontinuities4. Condition of
discontinuities5. Ground water condition6. Orientation of
discontinuities
ROCK MASS RATING VALUE (RMR):Based on this the rock mass
classification as per RMR is as shown in table 3.5 and
corresponding support system is given in table 3.6.In applying this
classification system, the rock mass is divided into a number of
structural regions and each region is classified separately. The
boundaries of the structural regions usually coincide with a major
structural feature such as fault or with a change in rock type. In
some cases, significant changes in discontinuity spacing or
characteristics, within the same rock type, may necessitate the
division of the rock mass into a number of small structural
regions.The first five of these parameters are grouped into five
ranges of values which are assigned specific rating to reflect
their influence on total rock mass quality. The rating of sixth
parameter is considered depending on orientation of tunnel with
respect to the strike and dip of the formation to arrive at the
final rock mass classification. By adding the relevant rating of
the above parameters , RMR has been calculated for the dominant
type of rock mass crossing the tunnel alignment.
Table 3.6: Support system corresponding to rock quality given in
RMR system
Rock mass class
Exacavation
Rock bolts (20mm dia., fully grouted)shotcrete
Steel sets
I-Verygood rockRMR: 81-100Full face, 3m advanceGenerally no
support required except spot bolting
II- Good rockRMR: 61-80Full face, 1-1.5m advance. Complete
support 20m from face.Locally, bolts in crown 3m long spaced 1.5-2m
with occasional wire mesh.50mm in crown where required.None
III- Fair rockRMR: 41-60Top heading and bench 1.5-3m advance in
top heading. Commence support after each blast.Complete support 10m
from face.Systematic bolts 4m long, spaced 1.5-2m in crown and
walls with wire mesh in crown.50-100mm in crown and 30mm in
sides.None
IV- Poor rockRMR: 21-40Top heading and bench 1-1.5m advance in
top heading.Install support concurrently with excavation, 10m from
faceSystematic bolts 4-5m long, spaced 1-1.5m in crown and walls
with wire mesh.100-150mm in crown and 100mm in sides.Light to
medium ribs spaced 1.5m where required.
V- Very poor rockRMR: 60mm5
3RQD60mm5
3RQD5mm0
RoughnessSmooth1
FillingSoft2
weatheringSlightly weathered3
5Ground water conditionWet7
6Dip and strife of main discontinuityFavorable-2
Total ratingRock mass ratingRock class37
Poor
IV
Table 3.9: Location: Banihal area, Phyllite/slate Machal
formationS.No.ParametersValueRating
1Strength of intact rock(UCS)100-250mpa12
2Spacing of discontinuities>60mm5
3RQD5mm0
RoughnessSmooth1
FillingSoft2
weatheringHighly weathered1
5Ground water conditionWet7
6Dip and strife of main discontinuityFavorable-2
Total ratingRock mass ratingRock class33
Poor
IV
Safe Bearing Pressure: Safe Bearing Pressure (SBP) of the rock
mass has been calculated by using RMR system. SBP has been
calculated for phyllite and quartziticphyllite of Ramsu formation
and phylliye/slate of Machal formation. All the above rock types
fall in poor category with total rating of 34, 37 and 33,
respectively. It is recommended that during construction. The net
SBP calculated on the basis of RMR system is given in table 3.10
below:Table 3.10: Net SBPClassification No.IIIIIIIVV
Description of rockVery goodGoodFair Poor Very good
RMR100-8180-6160-4140-2120-0
Qs (MP)6.0-4.54.5-2.92.9-1.51.5-0.60.6-0.4
Stand up time based on RMR classification has been calculated
for both the rock formation. The standup time for tunnel excavation
may be taken as 10 hours for 2.5 span.
Standard Penetration test:Standard Penetration test (SPT) have
been calculated in the drill holes along T-74R alignment. Though
empirical in nature, it is a practicable method to determine safe
bearing capacity of soil.The soil recovered in the bore holes is
generally hard, fine to medium grained silt/clay matrix with rock
fragment. From 1.5m-2.1m, 3.00-m-3.60m and from 4.50m-4.55m depth
in BH-1, N values recorded are 34, 47 and refusal to penetration,
respectively. In BH-2 from 1.50m-1.70m, refusal to penetration is
recorded, BH-3 has recorded refusal to penetration from 1.50m-1.55m
depth. In BH-4, SPT conducted from 6.00m-6.05m, 13.50m-13.53m,
34.50m-34.55m.Safe bearing capacity as IS 1904-1961for moist clay
mixture that can be identified with strong thumb pressure -15T/m2
for soft shale, hard rock stiff clay in deep bed ,dry, subject too
certain ground condition. Therefore, safe bearing capacity of soil
ranging between 15T/m2 and 45T/m2maybe considered.Through the above
value of empirical in nature but it gives an overall nature and
strength of the soil material in respect of slope stability
,foundation portal location ,filling material etc. however, it is
suggested to conduct in-situ load bearing tests before placing
foundation, slope stability measure, etc. to have exact
characteristics of the soil material.
Permeability Tests:Double packers tests have been conducted in
the northern end of the tunnel alignment towards Banihal, in BH-5A,
BH-5B, BH-7.the tests have been carried out to determine
permeability of the rock mass at different depths, as per IS-5529
specification .the formation grade lies between 40m to74m below
ground surface in this section.
S.NO.Borehole No.
Depth
Core No.
Rock Type
Remark
01
5A29.80-31.00
109
Fresh slatyphyllite
Fine grained schistose texture
025A35.00-35.70123Fresh slatyphyllite
Fine grained schistose texture
03
5A
46.00-47.00
169
Fresh slatyphyllite
Fine grained schistose texture
04
5A
49.00-50.00
185
Fresh slatyphyllite
Fine grained schistose texture
3.7 Geotechnical discussion:
The tunnel alignment run through highly fragile rock mass. The
bulk composition of the Ramsu formation and Mechal formation is
phyllite with minor quartzite, quartzitic bands in Ramsu formation
and agglomerate slate, tuff limestone in Mechal formation. The
phyllite are highly fracture and fragile due to intense folding and
faulting.In general the core recovery is moderately good but the
RQD is poor, indicating that the rock mass is highly fractured and
jointed deeptunneling (>200m) through such rock mass is
difficult task in HIMALAYAS where in-situ stress are high. Some of
the tunneling problems which are likely to meet with and remedial
measures are discussed.
Rock Bursting/Squeezing:In Himalayas the phenomena occurs in
deep tunneling in the areas of active in-situ stresses. As per
calculation based on thickness of rock mass over the tunnel and Q
value, the alignment lies in the safer zone. However this
phenomenon can also occur at shallow depths where the rock are
highly fragile and fractured andfolded. Suitable remedial measures
may be kept in readiness for such situation.
Over-break:Considering the poor quality of the rock, excessive
over break/chimney formations are likely to occur. Remedial
measures are grouting and heavy support may be kept in
readiness.
CHAPTER 04
TUNNEL MONITORING
4.1 IntroductionMonitoring section consists of 3D monitoring
ponits (DMP), Strain meters, Pressure cells and Multipoint (3 Point
and 2 Point) extensometers. In tunnel monitoring these instruments
are installed at proper sections after primary Shotcreting to
measure the deformation, squeezing and lateral and longitudinal
shifting of tunnel till the tunnel gets stabilized. The read out
unit gives readings of pressure cells, Strain meters and MPBXs
directly in engineering units and final linning is given to the
tunnel section. The details of the instrument are given below.
STRAIN METERSStrain has no units and we calculate it in micro
strains (s)Readings in s= [(F.R in digits I.R in digits) x G.F]
where G.F is in digit/mmLR initial reading is taken after the
installation of the strain meter on the wire mesh/lattice girder
(before Shotcreting). This is also called the zero reading. This
reading is subtracted from the subsequent reading which is taken
after shotcreting. F.R is final reading taken after shotcreting.G.F
gauge factor is provided with every instrument by the manufacturer.
It is different for each instrument.Range of strain meter is 1500
micro strain. ve sign indicates compressive strain and +ve sign
indicates tensile strain.Five- three pairs of strain meters have
been installed. One pair on crown, 2nd on left and 3rd on the right
hand side. For crown the strain meters are names as SS1I and SSM 1O
where 1 indicates crown position and I and O for the outer strain
meters, similarly SSM 2I for the left side and SSM 3I-3O for the
right side.
1. PRESSURE CELLSPressure cells are fixed on the lattice
girders. These measures the pressure of rock mass coming on the
lattice girder and pressure is indicated on the portable Readout
unit in MPa.
Reading in MPa = (F.R I.R) x G.F where G>F is in
digit/MPa
For pressure cell RPC-1 for crown (Radial pressure cell), RPC-2
for the left side and RPC-3 for the right side.
2. M.P EXTENSOMETERIn tunnel T-74R, 2-3 point extensometers are
being installed. The sensors are attached to the connecting fiber
glass rods at the mouth of MPBX housing. The convergence/divergence
of surrounding rock is measured on the portable Readout unit in
mm.
Reading in mm = (F.R I.R) x G.F where G.F is in digits/mm+ve
sign indicates rod of extensometer coming out of boreholes showing
divergence in the tunnel. -ve sign indicates rod of extensometer
going inside the borehole showing convergence in the tunnel.For
extensometer we use MRE-1, MRE-2, and MRE-3MRE 1-9 crown position
9m deep anchorMRE 1-6 crown position 6m deepMRE 1-3 crown position
3m deep
MRE 2-9 left position 9m anchorMRE 2-6 left position 6m deepMRE
2-3 left position 3m deep
MRE 3-9 right position 9m deep anchorMRE 3-6 right position 6m
deepMRE 3-3 right position 3m deep
Monitoring cross Sections (3D Monitoring Instrumentation)At the
start in the already excavated tunnel three DMPs have been
installed at every 50m interval. Further as excavation of tunnel
progressed, three DMPs are installed in heading and two in the
benchingMethod of ERT 10B_BiReflex TargetGeneral descriptionModel
Ert-10 bi reflex target consists of a reflector mounted on robust
frame. The target has reflector on both sides and is mounted on a
universal joint such that it can be oriented in any direction as
required. The target had a small center hole to allow precise
targeting.
It is made up of high performance material and precise
manufacturing processes. The target is thus interchangeable. The
target is high measuring accuracy so as to achieve the specified
measuring accuracy of 1mm. it is used along with the convergence
bolt and break off point. For the installation exact position is
located and a hole of 25mm diameter and depth of 220mm is drilled
in which the convergence bolt is grouted. The break off point is
mounted on the convergence bolt and bi-reflex target is fixed on
it. To find out actual convergence/settlement the coordinates
recorded earlier are subtracted from subsequent readings with the
help of TS.
SM-3
Section Type:S2LocationTunnel: T-74R North Portal Escape
Chainage:7247.25
Position : 19:30Hrs
Read out UnitModel EDI 51V
Instrument Name: Strain Meter, Range: 1500 strain
S.No.DateObservationTimeRemarks
SM2-ISM2-O
Ch. No. 273(e)Ch. No. 274(e)
118-03-20130.000.006.20Reading before shotcrete
219-03-20137-3513.00Reading before shotcrete
320-03-2013-34-10413.21Excavation in progress
423-03-2013-50-1209:21Excavation in progress
526-03-2013-90-13412.12
601-04-2013-123-14510.30
703-04-2013-135-15011.40
817-04-2013-140-16012.34
922-04-2013-136-17212.21
1029-04-2013-180-22312.10
1102-05-2013-176-22611.44
1204-05-2013-168-33411.22
1312-06-2013-168-35211:34
1414-06-2013-171-34710:32
1519-06-2013-165-32011:26
1621-06-2013-163-34011:09
1724-06-2013-161-34211:15
1810-06-2013-159-33911:35
1928-10-2013-257-33511:41
2029-10-2013-257-32811:50
2129-10-2013-256-43812:00
2226-11-2013-256-45112:30
2329-11-2013-255-44112:24
2404-11-2013-214-44211:00
2513-11-2013-172-44011:16
2604-12-2013-178-40611:20
2713-12-2013-212-39211:34
2816-12-2013-214-39211:30
2927-12-2013-258-44411:11
3011-01-2014-259-45211:40
3118-01-2014-258-45412:14
3225-01-2014-260-45812:20
3301-02-2014-258-45412:44
3410-02-2014-261-45613:28
3513-02-2014-278-45912:44
4.4 DEFORMATION MONITORING POINT DATA FOR NORTH PORTAL MAIN
TUNNELDATA ANALYSIS SHEET
Horizontal Displacement
Settlement
Vertical displacement
DATEChange in Easting from initial(x)(mm)Change in easting from
initial elevation(z)Change in northing from initial (y)
14-06-20130.000.000.000.000.000.000.000.000.00
15-06-2013-4.00-6.005.00-2.00-1.00-1.002.00-1.003.00
17-06-2013-6.00-7.004.00-3.00-2.00-2.003.00-2.003.00
19-06-2013-7.00-8.004.00-4.00-3.00-3.001.00-3.004.00
21-06-2013-6.00-7.004.00-4.00-3.00-3.000.00-2.003.00
24-06-2013-6.00-7.004.00-5.00-3.00-3.001.00-1.003.00
25-06-2013-7.00-7.003.00-4.00-3.00-3.000.00-2.003.00
27-06-2013-8.00-8.003.00-4.00-3.00-3.001.00-3.004.00
28-06-2013-7.00-7.004.00-4.00-3.00-3.001.00-1.004.00
29-06-2013-6.00-7.004.00-4.00-3.00-3.001.00-2.003.00
01-07-2013-7.00-8.003.00-4.00-3.00-3.000.00-2.004.00
01-07-2013-6.00-8.004.00-4.00-3.00-3.000.00-3.004.00
01-07-2013-7.00-8.003.00-4.00-3.00-3.001.00-2.003.00
01-07-2013-600-7.003.00-4.00-3.00-3.001.00-2.004.00
01-07-2013-7.00-8.004.00-4.00-3.00-3.000.00-2.003.00
4.5 MULTI POINT EXTENSOMETER DATA FOR MAIN TUNNEL NORTH
PORTALSection Type:S3LocationTunnel: T-74R North Portal Main
Tunnel
Chainage: 132738
Position : 12:00 Hrs
Read out UnitModel EDI 51V
Instrument Name: Multipoint rod Extensometer (MRE), Range:
50mm
S.No.DateObservationTimeRemarks
MRE 1-9MRE 1-6MRE 1-3
Ch. 260(mm)Ch. 261(mm)Ch. 262(mm)
102-03-20130.000.000.0012.00Base reading after grouting
202-03-20130.020.010.0210.23
302-03-20130.030.020.0211.00
402-03-20130.010.010.0111.34
502-03-20130.01-0.020.0011.40
602-03-20130.000.000.0011.50
702-03-20130.000.000.0112.12
802-03-20130.000.000.0012.23
902-03-20130.000.000.0013.12
1002-03-2013-1.00-1.00-1.0013.10
1102-03-2013-1.000.000.0011.56
1202-03-2013-1.00-1.00-1.0011.40
1302-03-2013-1.000.00-1.0011.23
1404-03-2013-1.00-1.000.0011.30
1506-03-20130.000.000.0011.55
1607-03-2013-1.00-1.00-1.0012.12
1709-03-2013-0.020.01-0.0213.11
1810-03-2013-0.01-0.01-0.0113.00
1911-03-2013-0.01-0.02-0.0212.18
2012-03-2013-0.02-0.03-0.0312.44
2113-03-2013-0.01-0.02-0.0211.55
2214-03-2013-0.01-0.01-0.0211.44
2315-03-2013-0.03-0.03-0.0411.12
2416-03-2013-0.08-0.08-0.0710.53
2518-03-2013-0.09-0.09-0.0910.40
2621-03-2013-0.09-0.07-0.0914.10
2722-03-2013-0.09-0.07-0.1010.23
2824-03-2013-0.09-0.10-0.1010.40
2928-03-2013-0.10-0.09-0.1011.40
3029-03-2013-0.10-0.09-0.1012.40
3130-03-2013-0.10-0.09-0.1014.21
3203-06-2013-0.09-0.09-0.1014.12
3305-06-2013-0.09-0.09-0.0911.40
3410-08-2013-0.09-0.09-0.0812.45
3513-08-2013-0.09-0.09-0.1011.50
3615-08-2013-0.09-0.09-0.0910.20
3717-01-2014-0.09-0.09-0.0910.50
3819-01-2014-0.09-0.09-0.1011.43
3910-02-2014-0.09-0.09-0.0910.22
05CONCLUSION
Conclusiona) T-74R consists of main tunnel and and escape tunnel
connected to each other by CPBs.b) The rock mass in PirPanjal range
is highly inhomogeneous hence NATM was adoptedc) Extensive
geological and geotechnical investigation was carried to decide the
design criteria.d) The overall rack mass is fair, hence light
lattice girder and rock bolting was done.e) Subsurface exploration
by boreholes along T-74R alignment was carried out to understand
quality of rock mass at the formation grade.f) The bulk composition
of rock mass of Ramsu and Machal formation is commonlyphyllite with
minor quartzite, phyllite/slatyphyllite and agglomerate slate.g)
The rocks are thinly foliated, highly fragile and fractured in
nature and intensely deformed due to faulting and folding.h) Core
recovery varies from 0 to 99% and RQD from O to 95%. The Q value of
phyllite, quartziticphyllite of the formation varies between 0.33
to 0.83.i) Recommended maximum unsupported span of phyllite varies
from 1 to 2 m for poor rock class.j) RMR for phyllite,
quartziticphyllite varies from 33 to 37 for poor rock class.k) On
the basis of RMR stand up time may be 10 hrs. For 2.5m span.m) The
soil is inhomogeneous in Present 0356 hence NATM is Preferred over
TBM.n) The deformation, squeezing and lateral movements of tunnel
were observed and it was found that deformations were within
permissible limits in almost all cases.
06PHOTO GALLERY
Image 02a taken at the site
37
