internship report geological engg. uet lahore 2

Neelum Jhelum Hydroelectric Project

NJHP: C2 of 32

Internship Report Geological Engg. UET Lahore 2.docx

Prepared By: Faisal Hayat

Checked: Muhammad Bilal (Asst. Director Geology) Date: 22nd June 2016

TRAINING PROGRAMME

NEELUM JHELUM HYDROELECTRIC PROJECT LOT.C2

SUBMITTED BY:

FAISAL HAYAT

Department of Geological Engineering

University of Engineering and Technology Lahore


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CONTENTS

ACKNOWLEDGEMENT AND GRATITUDE’S: ....................................................................... 4

1. INTRODUCTION TO THE PROJECT: ......................................................................... 5

1.1 PROJECT OVERVIEW: .............................................................................................. 5

1.1.1 LOT C1: ..................................................................................................................... 5

1.1.2 LOT C2: ..................................................................................................................... 6

1.1.3 LOT C3: ..................................................................................................................... 7

1.1.3 REGIONAL GEOLOGICAL OVERVIEW OF THE PROJECT: ........................................ 7

1.1.3 NE-SW REFOLDING STRUCTURES: ......................................................................... 9

2. TUNNELS AND TUNNELING: ................................................................................... 10

2.1 TERMS REALTED TO TUNNELING: ......................................................................... 10

2.2 SHAPES OF TUNNEL: ............................................................................................. 12

3. TUNNEL EXCAVATION METHODS: ......................................................................... 13

3.1 DRILL AND BLAST METHOD: .................................................................................. 13

3.2 EXCAVATION BY TBM: ............................................................................................ 14

3.2.1 MAJOR COMPONENT OF TBM: ............................................................................... 14

3.2.2 OPERATING SEQUENCE OF TBM: .......................................................................... 16

3.2.3. SECTIONS OF TBM: ................................................................................................ 16

3.2.4. COMPARISON b/w TBM AND DRILL AND BLASTING: .............................................. 16

4. DESIGN OF SUPPORT FOR THE ROCK AFTER EXCAVATION: ............................... 17

4.1. ROCK CLASSIFICATION SYSTEM:............................................................................. 17

4.2. BASED ON Q-VALUE THE FOLLOWING ROCK CLASSES ARE IDENTIFIED: .............. 18

4.3. BEHAVIOUR OF ROCK IN DIFFERENT GROUNDS:.................................................... 18

5. SUPPORT AFTER EXCAVATION: ............................................................................ 19

5.1. 1st LAYER OF SHOTCRETE: ...................................................................................... 19

5.2. ROCK BOLTS: ............................................................................................................ 19

5.3. WIRE MESH/ STEEL RIBS/ LATTICE GIRDERS FIXING: ............................................. 20

5.4. 2ND LAYER OF SHOTCRETE: .................................................................................... 20

5.5. SWELLEX: ................................................................................................................. 21

5.6. GROUTING: ............................................................................................................... 21

5.7. CONCRETE LINNING: ................................................................................................ 22

6. INVERT CONCRETE:............................................................................................... 23

6.1. STEPS FOR INVERT CONCRETING: ..........................................................................24


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6.1.1. CLEANING OF THE INVERT:....................................................................................24

6.1.2. FORMWORK INSTALLATION: ..................................................................................25

6.1.3. CONCRETE POURING: ............................................................................................25

6.1.4. REMOVAL OF THE FORMWORK: ............................................................................26

7. FINISHING GANTRY:. .............................................................................................27

7.1. DRUMMY AREA MARKING:: .......................................................................................27

7.1.1. GROUTING IN DRUMMY AREA:: ..............................................................................28

7.1.2. PRESSURE TESTING:: ............................................................................................28

7.1.3. COMPLETION OF GROUTING:: ...............................................................................29

7.1.4. EQUIPMENTS USED IN GROUTING::.......................................................................29

7.2. CRACK MARKING::.....................................................................................................30

7.3. THICKNESS TEST:: ....................................................................................................31

7.4. CONTOURING:: ..........................................................................................................31

7.5. PROTRUDING STEEL FIXTURES:: .............................................................................31

8. REFERENCES: .........................................................................................................32


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ACKNOWLEDGEMENT AND GRATITUDE’S:

I am very thankful to WAPDA and NJHPC for arranging such an informative

internship for me at NJHP that is made possible because of WAPDA. I am also thankful to all

the staff of FINISHING GANTRY office for giving me time and collecting me information.

This internship not only enhanced my field knowledge about tunnelling but also has given

me an opportunity to work alongside with engineers. I think this type of training program

should be given to every student who wants to broad his knowledge of tunnelling. I am very

hopeful that more and more internees will be entertained from this type of training

program in future.


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1. INTRODUCTION TO THE PROJECT:

1.1. PROJECT OVERVIEW:

Project is located in the vicinity of Muzaffarabad (AJ&K), 121 Km from Islamabad, Pakistan.

It envisages the diversion of Neelum river water through a tunnel out falling into Jhelum

River and has installed capacity of 969 MW. Concrete gravity dam with reservoir capacity

of 2.80 MCM and designed discharge of 280 m3/sec, provides 420m head to powerhouse.

Neelum Jhelum Hydroelectric Project consists of following construction sites. Over all

project layout is briefed in cross-section map in Figure.

1.1.1. LOT C1

Lot C-1 has construction of Access Tunnel A-1, Dam site, Diversion Tunnel, Six gate tunnel

intake structure located 41 Km East of Muzaffarabad at Neelum River.

1.1.2. LOT C2

Lot C-2 includes construction of Access Tunnels A-2, A-3, A-4 & A4a, Jhelum River Crossing

via twin tunnels at 177 meter deep from River Bed, single headrace tunnel leading to

underground powerhouse and two Main Beam Hard Rock TBM (boring towards dam site

C1). Lot C2 is located 22 Km from Muzaffarabad on Srinagar Road at Jhelum River.

Following Figure 2 shows scope of work at Lot-C2

Figure 1:Section represented by blue rectangle covers scope of tunneling work at Lot-C2


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Figure 2: Work Scope of Lot C2 and General Layout

1.1.3. LOT C3

Lot C-3 has construction of Access Tunnels A-5, A-6, A-7 & A-8, Surge Chamber, Surge Shaft,

UG Power House and UG Transformer Hall. Lot C3 is located 21 Km South of Muzaffarabad

near Jhelum River.

1.2. REGIONAL GEOLOGICAL OVERVIEW OF THE PROJECT:

The geology of the Neelum Jhelum Hydropower Project (NJHPP) is characterized mainly by

molassic sedimentary rocks of the Murree Formation, which is of Paleocene to Eocene age.

These rocks were deposited in the flexural fore deep basin formed by the rising Himalayan

Ranges, which developed as a result of the collision of the Indian Plate and its accreted

Kohistan Arc with the Eurasian Plate in the Kashmir region of Pakistan. The project is

located in the Sub Himalaya, on the edge of the Himalayan chain, as shown by the red bar in

the schematic cross-section in Figure 3


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Figure 3: Techtonic Cross-section of Central Himalyayen Domain

In the project area, the major faults such as the Main Boundary Thrust (MBT) that run the

length of the Himalayan Range, and which separate the younger Tertiary rocks from the

older rocks forming the Higher Himalaya, twist through a 180-degree, northwest trending

bend known as the Hazara Kashmir Syntaxis (Figure 2). The 32.2 km long, southeast

trending tunnels of the NJHPP cross almost the entire width of this syntaxis.

The project’s intake dam on the Neelum River is located on the MBT itself, with the right

abutment composed of the igneometamorphic Panjal Formation and the left abutment

composed of the Murree Formation. The headrace and tailrace tunnels will be excavated

entirely through the Murree Formation, and will cross the active Muzaffarabad Fault (also

known as the Balakot Bagh Fault) to an underground power house located close to the

Jhelum River, where the MBT is encountered once more, having curved through 180

degrees around the margin of the Hazara Kashmir Syntaxis.

The Murree Formation is composed of strong grayish sandstone, reddish brown sandstone

and siltstone [good to fair rock mass], reddish brown mudstone [fair to poor rock mass]

and rare shale [poor to very poor rock mass]. Sheared mudstone is sometimes confused

with shale.

The Murree Formation has traditionally been described as a monotonous series of

alternating beds of shales and sandstone, and this terminology was used during previous

investigations up to and including the detailed design stage. However after construction

commenced, it became clear that interbedded siltstones and mudstones are encountered

far more commonly than shale at all the three project sites.


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Structurally the formation shows a high degree of compression in the form of tight folding

with repeated faulting and fracturing. At places, it shows open broad folds which have been

weathered into steep ridges and valleys with a succession of escarpments and steep slopes.

However, what is advantageous to the project is that the axes of the folds mostly strike

perpendicular to the main waterway tunnel alignment, meaning that bedding strikes are

crossed at steep intersection angles. Short auxiliary tunnels that run parallel to the

bedding strike invariably suffer far more stability issues than those crossing the bedding

strike at steep intersection angles.

The 2005 Muzaffarabad earthquake (magnitude 7.6 on Richter Scale), historically the

largest earthquake recorded in the Himalayan Range, was caused by rupture along a 113

km long segment of the Muzaffarabad Fault (shown by the yellow dashed line in Figure 2)

.The project’s headrace tunnel will cross the ruptured segment, which at the surface

showed a displacement of 3-7 m.

Figure 4: Techtonic Setup in the vicinity of NJ-Project


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1.1.1. NE-SW REFOLDING STRUCTURES:

The Muzaffarabad Anticline and related structures, including the Muzaffarabad

Thrust, which mark the first phase of structures in the Hazara Kashmir Syntax is, are

refolded through a subsequent phase of deformation. The structures related with this

folding are oriented ENE-WSW, almost at right angle to first-phase structures and thus

result in their refolding. About three such folds refold the core of the Muzaffarabad

Anticline in the vicinity of Muzaffarabad. The largest of these refold structure is defined by

the Neelum reentrant, whereby the axis of the Muzaffarabad Anticline as well as the

Muzaffarabad Thrust form a NE trending fold structure around the Neelum River as it

enters Muzaffarabad. Greco (1989) have shown that this phase of folding is widespread in

the Hazara Kashmir Syntaxis as well as in the lesser and Higher Himalayas in the Kaghan

area.

Figure 1.1 Geological Setup


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2. TUNNELS AND TUNNELING: A tunnel is an artificial underground passageway, completely enclosed except for

openings for entrance and exit, commonly at each end. The underground structure of

tunnel i.e. relatively uniform cross section and significant length used for purposes of

transportation, shelter, or storage. Tunneling is a technique to construct a tunnel.

2.1. TERMS RELATED TO TUNNELING:

o PORTALS:

The entry and exit points of a tunnel are known as portals. Each tunnel has two portals,

which are named after their geographic locations or their location in project, e.g. South

Portal, North Portal, Inlet Portal and Outlet Portal.

o INVERT:

The floor/bottom of the tunnel OR the invert of a tunnel is the slab on which the roa dway

or track bed is supported. In a circular shaped tunnel, this is the bottom portion of the arc.

In a horseshoe shaped tunnel, this is the flat bottom.

o FACE:

The vertical wall that is excavated for the advancement of a tunnel.

Fig.2 Tunnel Shape


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o CROWN: The highest part of a circular or horse shoe shaped tunnel. Also called the “roof”.

o WALL: The distance between the invert and crown is called wall OR the distance between invert

and spring line. It may be right wall and left wall with respect to an observer.

o COVER: Cover is Overburden of rock or soil in feet or meters on the arch of a tunnel.

o FULL-FACE HEADING: An excavation of the whole tunnel faces in one operation.

o CUTTER HEAD: The front end of a mechanical excavator, usually a wheel on a tunnel boring machine that

cuts through rock or soft ground.

o OVERBREAK: The quantity of rock that is actually excavated beyond the perimeter established as the

desired tunnel outline.

o BENCH: Part of the lower tunnel section left temporarily unexcavated as excavation of a heading is

advanced on top of it.

o INITIAL SUPPORT: Tunnel support placed at the heading following excavation to maintain stability and safety

of the opening and to minimize ground movement.

o FINAL SUPPORT: Tunnel support or lining installed following initial support and independent of excavation

to complete lining installation.

o ACCESS TUNNEL: A short tunnel from a shaft or from the surface to a main tunnel or connecting two main

tunnels.

o MUCK: Broken rock or other material produced at the face of a tunnel by the excavation process.

o DIAMETER/WIDTH OF THE TUNNEL: The maximum horizontal distance between walls of the tunnel.


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o HEIGHT OF THE TUNNEL: The maximum vertical distance between invert and crown of the tunnel.

o GROUND CONTROL: Any technique used to stabilize a disturbed or unstable rock mass.

2.2. SHAPES OF TUNELS:

To design the shape of the tunnel there should be the idea of the in situ stresses because shape of

the tunnel is considered as major parameter for the stability of the tunnel along with the

geological conditions. Selection of the shape of the tunnel depends upon the geological

conditions, ground water conditions and geological structures. There are four main shapes of

tunnels:

1) Circular 2) Rectangular 3) Horseshoe 4) Oval/egg

The shape given to the NJHP is circular because of the geological setup of the area and past

study of the area. Also for the smooth movement of the water.

Figure 2.2 Shape of headrace tunnel NJHPP


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3. TUNNEL EXCAVATION METHODS: The tunnels can be excavated through the following methods:

A) By Drill and blast Method

B) By Mechanical Method (Through TBM)

3.1. DRILL AND BLAST METHOD:

Drill and blast method is mostly used method for the excavation throughout the world. The

method can be used in all types of rocks and the initial cost is lower than the mechanical

method like TBM. This tunneling method involves the use of explosives. Drilling rigs are

used to drill blast holes on the proposed tunnel surface to a designated depth for blasting.

Explosives and timed detonators (Delay detonators) are then placed in the blast holes.

Once blasting is carried out, waste rocks and soils are transported out of the tunnel before

further blasting. Hence adequate structural support measures are required when adopting

this method for tunneling.

Compared with bored tunneling by Tunnel Boring Machine, blasting generally results in

higher duration of vibration levels. A temporary magazine site is often needed for

overnight storage of explosives. The excavation rate is also less than TBM (usually 3 to 5m

a day).

The Drill and Blast method were used in NJHP (C1, C2 and C3), but after the arrival of TBM

the excavation were started by using TBM (at C2).

Figure 3.1 Drill and Blast Cycle


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3.2. EXCAVATION BY TBM:

Tunnel construction by means of TBM (Tunnel Boring Machine) has become a preferred method

of construction nowadays. In addition, this is well accepted by the environmentalist and the

green groups. This state-of-art technology limits all works underground in building the tunnel to

keep the disturbance to land, wildlife and mankind activities at ground level to a minimum

throughout the period of construction.

Tunnel construction by TBM is quite different from the traditional Drill and Blast Method. The

tunnel is excavated by means of a machine instead of blasting with explosive. The tunnel lining

is put in place at the back of the machine immediately following a ring length of TBM

advancement.

3.2.1 MAJOR COMPONENT OF TBM :

S.NO COMPONENT FUNCTION

1 Disc Cutter To excavate rock or soft ground by the rotation of an assembly of teeth or

cutting wheels under pressure against rock face.

2 Shield To keep the soil from getting into the machine and to provide a safe space for

the workers

3 Pushing Jack To be in full contact with the erected segment and extend by hydraulic as the

cutter disc turns and thrusts forward.

4 Main Drive To provide a force in rotating the cutter disc and is powered by electricity.

5 Screw Conveyer

To move the spoil at the cutter disc and feed onto a conveyor system.

6 Erector To erect the segments to form a complete ring after shoving at the tail of the

TBM. 7 Back up

Facilities

To travel with the TBM and to service the operation of annular grouting,

welding, extension of ventilation, power and track etc.

8 Control Room The control room used to control the main functions of the TBM like penetration rate, thrust, advance speed, Rotation per minutes, camera control, conveyer belt control, tunnel direction, Grippers and hydraulic jacks etc. The thrust shows the geology of rock like if the thrust is increasing then the rock is hard (sandstone) and so we should increase the advance speed and If the thrust is decreasing then it has soft geology and the advance speed should be decreased because increased speed at soft geology causes collapse

9 Rear Support It is a support that provides the support when TBM moves forward after excavation of 1.8m ahead.


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Figure 3.2.1 Components of TBM


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3.2.2. OPERATING SEQUENCE OF TBM:

The Gripper TBM, often also widely described as open TBM, is the classic form of tunnel

boring machine. The area of the operation is mostly hard rock with medium to high stand

up time. In order to be able to produce the thrust behind the cutter head, the machine is

braced radially against the tunnel wall by hydraulically moved clamping shoes, the so

called grippers. The Grippers grips the wall of the tunnel during operation. When a cycle

(1.2m) completes, the grippers are retracted and the rear support expands. The TBM then

moves and the grippers again grips to the wall of the tunnel.

There are two Hard Rock Gripper TBM’s are working in NJ project which are 696 and 697

(manufacturer named it). They are working in the left and right twin tunnels. The TBM’s

using in the NJ has been borrowed from HK Company (Germany). Total length of this TBM

is 190m. But the average lengths of latest TBM’s are 410m. Daily progress may reach to

maximum 15m but average is 8 to 10m in a day. Power engines are used to provide the power

to the whole assembly of the TBM. The power is being provided from the HFO (high fuel

oil). The HFO provides 16MW power to the whole C2 Project area.

3.2.3. SECTIONS OF TBM: TBM is divided into three sections L1, L2 and L3. o L1 is used for temporary support like 1st layer of shotcrete.

o L2 is used for permanent support like rock bolts, Wire mesh Ring beam and 2nd layer of

shotcrete. The criteria for the supports are the same as already described in D & B

section.

o L3 is used for the storage of material.

3.2.4. COMPARISON b/w TBM AND DRILL AND BLASTING:

Drill & Blast TBM

Not Much Safer Improved personal safety Can blast any type of rock Minimal ground disturbance

Ground vibration is much more Reduced ground support needed

Operation cost is less as compared with TBM Minimum overbreak, thus less material to move

Needs less technical staff Minimal ground vibration or air blast

Needs concrete lining Uniform muck size

Loaders and dumpers are required for mucking Continuous operations

Much support is required higher production rates


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4. DESIGN OF SUPPORT FOR THE ROCK AFTER EXCAVATION: After the excavation of the rock by TBM the support is designed. The first step to design the

support is to do Geological Mapping and note different parameters. Mapping of orientation

(Dip angle, Dip direction), Persistence, Spacing of joint sets, Infilling material, Roughness,

shape and aperture from exposed face, crown and walls and support recommendation after

rock mass evaluation using Q-system.

Using tables for the Q system, support is designed. The following supports are mainly used

in tunnels according to the Q value. Support consists of Shotcrete (Plain, SFR), Rock bolts

(Swellex, Fully grouted Rock bolt, Expansion shell, Spiles, Ribs), Lattice girder, UPN

channel, Ring beam, Grouting (High pressure and Low pressure). The size and type of

support changes as the rock type and other parameters changes. Support increases as the Q

value decreases. Also the size and diameter of the support changes with the Q value.

4.1. ROCK CLASSIFICATION SYSTEM:

THE Q SYSTEM (QUALITY INDEX):

The Norwegian Geotechnical Institute proposed a Tunneling Quality Index (Q) for the

determination of rock mass characteristics and tunnel support requirements. At the

Neelum Jhelum hydropower project the Q4 is divided in to Q4-A and Q4-B because of the

requirement at this project. 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:

Where

R.Q.D= Rock Quality Designation, Jn= is the joint set number

Jr= is the joint roughness number, Ja = joint alteration number

Jw= joint water reduction factor, S.R.F= the stress reduction factor

Q = (R.Q.D)/Jn × Jr/Ja × Jw/(S.R.F)


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4.2. BASED ON Q-VALUE THE FOLLOWING ROCK CLASSES ARE IDENTIFIED:

Q Systems Q value Quality

Q1 Above 40 V.Good

Q2 11 ~ 40 Good

Q3 5 ~ 10 Fair

Q4 1 ~ 4 Poor

Q5 > 1 Extremely Poor

4.3. BEHAVIOUR OF ROCK IN DIFFERENT GROUNDS:

S.NO. Ground Rock Behavior

1 Competent self-supporting Massive rock mass requiring no support for tunnel

stability

2 Incompetent non-squeezing Jointed rock mass requiring support for tunnel stability

3 Ravening Chunks or flakes of rock mass begin to drop out of the arch or walls after the rock mass is excavated

4 Squeezing Rock mass squeezes plastically into the tunnel and the

phenomena is time dependent; rate of squeezing depends upon the degree of overstress; occurs at shallow depths in

weak rock masses like shales, clay, etc. hard rock masses under high cover may experience slabbing/rock burst

5 Swelling Rock mass absorbs water, increases in volume and

expands slowly into the tunnel, for example montmorillonite clay

6 Running Granular material becomes unstable within steep shear zones

7 Flowing A mixture of soil like material and water flows into the

tunnel. The material can flow from invert as well as from the face crown and wall and can flow for large distances

completely filling the tunnel in some cases

8 Rock burst A violent failure in hard and massive rock masses when subjected to high overstress


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5. SUPPORT AFTER EXCAVATION:

5.1. 1st LAYER OF SHOTCRETE:

Shotcrete is a mixture of water, cement, aggregate and some chemicals which is sprayed

6cm thick first layer of fiber reinforced shotcrete after flushing the surface with

pressurized air & water. Shotcrete may be plain or reinforced. Fig.5.1

5.2. ROCK BOLTS:

Rock bolts are installed in the drilled holes that support the roof and walls of the tunnels.

These are simple and easy support. Mostly the rock bolts are drilled in the roofs using

TBM automatic system. Installation involves grouting of clean drilled holes with cement-

sand grout (1:1) then inserting rock bolts Φ=25mm; 4m long (3.9m inside rock). Shown

in fig.5.2

Figure 5.1 Shotcreting

Figure 5.2 Rock Bolts


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5.3. WIRE MESH/ STEEL RIBS/ LATTICE GIRDERS FIXING:

Fixing welded wire mesh (4.2x100x100 in mm), steel ribs (distribution bars Φ=10mm @

40-50 cm to keep the main bars Φ=16mm @ 10-20 cm in position) and lattice girders (1-

2m spacing).

5.4. 2ND LAYER OF SHOTCRETE:

Spraying 8-10cm thick second layer of fiber reinforced Shotcrete after flushing the surface

with pressurized air & water. Shown in fig.5.4

Figure 5.4 Shotcreting 2nd

layer

Figure 5.3 Wire Mesh installation


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5.5. SWELLEX:

Swellex is a type of bolting used to provide much support and make the joints squeezed so

the joints in the tunnel have to come closer. The swellex is inserted into the hole and

hydraulic pressure of 240 bars is applied through a pressure apparatus, the swellex

becomes expands in the hole providing support.

5.6. GROUTING:

Grouting is a technique which is used to remove the water from a tunnel (before and after

excavation) and to fill the cavities (joints) in the rocks. Grouting is a mixture of water,

cement and accelerator.

Figure 5.5 Swellex

Figure 5.6 Grouting


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5.7. CONCRETE LINNING:

The final lining of a tunnel is the permanently visible visiting card of the tunneling

contractor.

The exception is a final lining with paneling. Inner lining concrete (shell concrete) and

sprayed concrete are both used for a durable final lining. The higher the specifications for

the evenness of the concrete finish, the more likely it is that a lining of structural concrete

with interior ring forms will be used. The assembly used for the concrete lining are called

Needle beam form work. The assembly can move easily from one place to another place.

The lining can be done upto 12m in a single turn.

Figure 5.7 Concrete lined tunnel

Figure 5.7 Needle beam form work


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FINISHING WORKS OF THE TUNNEL: Finishing works includes concreting of the invert that is left over and Gantry work.

Finishing works is divided into eight phases. Now phase 1 is in progress at both the tunnels

(Headrace twin tunnels).

6. INVERT CONCRETE:

The invert at the tunnel that is left is concreting by the Finishing works. The left over invert

is in between 4'oclock to 8'clock area, making an angle of 100° from the centre of the

tunnel. The process of concreting is in both the twin tunnels. Before the actual concreting of

the invert trials were taken for different areas of the tunnels. After the successful trials,

different parameters and different types of materials were selected like the diameter of the

steel bars (used below the concrete), the strength of the steel bar, the strength of the

concrete and the thickness of the concrete. Here are some calculations to find out the

volume used for different lengths (w) in invert.

Radius of the tunnel (r) = 4.3m

Length of the tunnels where concrete is to be used (w) = 6m (Suppose)

Angle between the two points from the centre of the tunnel (α) = 100°

Thickness of concrete (T) = .20m

So, to find the:

Distance between two points of the invert 4 to 8'o clock (l) = rα

l = 4.3×

l = 7.50m

Now to find the volume of concrete used for the length of 6m we have:

V = l×w×T

V = 7.50×6×.20

V = 9m3


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6.1. STEPS FOR INVERT CONCRETING:

6.1.1. CLEANING OF THE INVERT:

First of all the invert is cleaned from water and other garbage. The cleaning process can be

done by using mini excavators, mini diggers or by man power. The cleaning of invert is

necessary because, to get the desired thickness for concrete, to get maximum strength from

the concrete and also to avoid the mixing of water with the mixture of concrete. After the

cleaning process the wire mesh is installed on the invert.

Figure 6 Calculation of the volume of invert

concrete

Figure 6.2.1 Cleaning of Invert


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6.1.2. FORMWORK INSTALLATION:

After the cleaning of the invert, steel bars are installed in the invert and wire mesh is tied

on that steel bars and then formwork is installed on the invert of the tunnel. Also latter

boxes are installed near the construction joints to get the natural strength from the

concrete.

6.1.3. CONCRETE POURING:

Concrete is taken to the site by vehicles. Before the pouring process, slump test is carried

out to find the workability of the concrete. The concrete is poured from the vehicle into the

form work and is driven into the invert. A vibrator is used during the pouring process to

make sure that there are no bubbles produced in the concrete and also to move the

concrete into every point of the invert.

Figure 6.2.2 Form work installation

Figure 6.2.3 Concrete pouring


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6.1.4. REMOVAL OF THE FORMWORK:

After the successful process the concrete is left to dry for few hours, when the concrete is

fully dried, the formwork is removed and a core is collected from the area for finding the

strength of the concrete. Hence the process is repeated accordingly.

Figure 6.2.4 Removal of Form work

Figure 6.2.4 Core of the concrete area


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7. FINISHING GANTRY: A gantry is a 25m (may be 12.5m of two) long frame body which is used for finalization of

the tunnel work. It consists of different instruments like grouting apparatus, water pump,

drilling apparatus and other small equipment. Gantry move on the rail track. The following

functions can be done on finishing gantry:

7.1. DRUMMY AREA MARKING:

Drummy area is that area which shows that either there is no contact between the final

support and the rock strata or the final support has hollow area in it. Drummy area can be

checked by using geological hammer that gives specific sound. Shallow drummy area (D s)

is left untreated while the drummy (D) area which is hollow is treated by using grouting.

Figure 7 Gantry

Figure 7.1 Drummy marking


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7.1.1. GROUTING IN DRUMMY AREA:

Grouting is a mixture of water and cement. The ratio is taken as 1:1 of water and cement

(Thin grout), and other chemicals. Once drummy area is marked by D sign, drilling is done

in that area (holes may be 3 or 2) and PVC pipe is inserted in it. The grouting machine is

started and grout is injected in that pipe. Contact grouting of low pressure (3 bars) is used.

Contact grouting involves the filling of void space between a cast-in-place (CIP) structure

and the in-situ geo-material or another structure. It may be similar to annular space

grouting, however, when contact grouting, normally the extent of the void space is not

known. Generally, the intent of contact grouting is to increase the structural integrity of the

structure. Contact grouting is often done in association with CIP liners for tunnels, shafts,

mine plugs, etc.

7.1.2. PRESSURE TESTING:

Pressure testing as used in drilling and grouting operations is the measured injection of water into

a grout hole prior to grouting. Pressure washing is the term applied to washing cuttings and other

filling out of openings in the rock intersected by the hole. Both operations are done through a

packer set in the hole or through a pipe grouted in the top of the hole. Pressure testing is used

primarily to determine whether grouting is needed. If the hole does not take water at a given

pressure, it will not take a grout containing solids at that same pressure.

Figure 7.1.1 Grouting in drummy area


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7.1.3. COMPLETION OF GROUTING:

(a) Grouting may be continued to absolute refusal at the maximum grouting pressure,

although this is not usually done. There are two methods that are most frequently used to

determine when grouting is complete. One specifies that grouting shall continue until the

hole takes no grout at three fourths of the maximum grouting pressure. The other requires

that grouting continue until the hole takes grout at the rate of 1 cu ft or less in 10 min

measured over at least a 5-min period. This is often modified according to the mix and/or

pressure used. The second specification is more readily correlated with pressure -test

results than the first.

(b) If there is doubt about the completeness of treatment in any zone or area, a check hole

or holes should be drilled. Such holes can be drilled to recover core for examination, or they

may be drilled for study by the borehole camera or television camera. However, a quicker

and less expensive check can be made by drilling and pressure testing another grout hole. If

tight when pressure- tested with water, the rock is satisfactorily grouted; if the hole takes

water, additional grouting is indicated.

Grout can provide:

o Increase strength and rigidity

o Reduce ground movement

o Groundwater control

o Predictable degree of improvement

7.1.4. EQUIPMENTS USED IN GROUTING:

LOGGER:

Figure 7.1.4 Logger


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Logger shows four parameters:

o Pressure: Pressure is controlled by pressure valve; while the pressure sensor is

connected to the logger shows the pressure in the logger screen. The pressure must be

between 2.5 and 3 bars. If the pressure is less than 1 then it indicates that the grouting

is finished and it should be stopped. The control of grouting pressures is vital to the

success of any grouting operation. This control is maintained by gages on the pump and

at the collar of the hole. The grouting inspector must determine that the gage at the

collar of the grout hole is accurate. Most grouting is done at pressures approaching the

maximum safe pressure. An inaccurate gage, especially one that registers low, could

result in the spread of grout into areas beyond any possible usefulness, or in wasteful

surface breakouts, or in damage to a structure by displacing rock in its foundation. In

such instances, grout is not only wasted, but the quantities injected may make tight

ground seem open and require intermediate holes to check the adequacy of the work. A

new gage is not necessarily accurate.

o Total quality: It shows the total quality of grouted injected in the whole process.

o Quality per minute: It shows the quality being injected per minute.

o Ratio of water and Cement: Thin grout ratio is 1:1 (water and cement). Density is

calculated and ratio (1.44 to 1.60) is being taken. If the ratio decreases from 1.44 then

cement is added to the grout and if it is above 1.60 then water is added to it.

MIXER is used to mix the components (water, cement and chemicals). AGITATOR agitates

the mixture so that the mixer does not get hard. Agitator pushes the mixer to the pump.

PUMP is used to pump the grout with pressure.

7.2. CRACK MARKING:

Cracks accessed area is marked with a zigzag marking which shows that the crack should

be treated properly. The marked area is left untreated for now and will be treated in the

next phase.

Figure 7.2 Crack marking


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7.3. THICKNESS TEST:

Thickness test is done in area where the thickness of the shotcrete looks less. In these areas

drilling is done to and the measurement inside the hole is noted. If the thickness is less than

the desired thickness then it is marked and later on shotcreting will be done on that area.

7.4. CONTOURING:

In contouring to find the roughness of the wall. Peak and trough are marked by using

measuring tape. For upstream the ratio between peak and trough is 1:12 and for

downstream the ratio is 1:25. If the ratio deviates from the desired ratio then treatment is

done at that area.

7.5. PROTRUDING STEEL FIXTURES:

Steel (Rock bolt etc.) that can be seen outside of the wall can be cut to the desired length.

The protruding of the steel could do more harm as when the water will be driven from the

upstream. The water will hit the steel and could cause failure of the tunnel area. So cutters

are used to cut these types of steels etc.

Figure 7.3 Thickness check


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8. REFERENCES:

o Literature data

o Syed ali turab research paper

o Engineer at different sites

o Finishing works office

Figure 7.5 Protruding steel