Chapter 12

Gongri Hydroelectric Project Feasibility Report

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TABLE OF CONTENTS

PAGE NO 12. CONSTRUCTION METHODOLOGY AND EQUIPMENT PLANNING........................12-1

12.1 INTRODUCTION ...................................................................................................12-1

12.2 BASIS FOR STUDY ..............................................................................................12-1

12.2.1 Major Components ............................................................................12-1

12.2.2 Material Sources ...............................................................................12-2

12.3 BASIC CONSIDERATIONS ....................................................................................12-2

12.3.1 Number and Type of Construction Contracts, Basic Hypothesis ........12-2

12.3.2 Scheduled Working Hours .................................................................12-3

12.4 CONSTRUCTION SCHEDULE ................................................................................12-4

12.5 PRECONSTRUCTION ACTIVITIES...........................................................................12-4

12.6 TENDER AND CONTRACTS...................................................................................12-5

12.7 MATERIAL SOURCES ..........................................................................................12-5

12.8 BARRAGE & INTAKE: CONSTRUCTION METHODS & EQUIPMENT ............................12-7

12.8.1 Surface Excavation............................................................................12-7

12.8.2 Concreting: Construction Methods and Equipment............................12-9

12.8.3 Construction Programme.................................................................12-10

12.9 FEEDER AND LINK TUNNELS .............................................................................12-11

12.9.1 Excavation.......................................................................................12-11


12.10 DE-SILTING BASINS..........................................................................................12-14

12.10.1 Construction Method and Equipment...............................................12-14

12.10.2 Construction Program......................................................................12-17

12.11 HEAD RACE TUNNEL ........................................................................................12-17

12.11.1 Construction Method & Equipment ..................................................12-17


12.12 SURGE SHAFT..................................................................................................12-21

12.12.1 Construction Method and Equipment...............................................12-22


12.13 PRESSURE SHAFT ............................................................................................12-25

12.13.1 Construction Method .......................................................................12-25


12.14 POWERHOUSE COMPLEX ..................................................................................12-27

12.14.1 Construction and Equipment ...........................................................12-28



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12.14.3 Electro-Mechanical Equipment .......................................................12-29

12.15 REQUIREMENT OF CONSTRUCTION EQUIPMENT ..................................................12-29

12.16 KEY MATERIAL REQUIREMENT/ PLANNING.........................................................12-29

12.16.1 Quantity of different materials..........................................................12-29

12.16.2 Coarse and Fine Aggregates...........................................................12-30

12.16.3 Cement and Steel............................................................................12-30

12.16.4 Explosives .......................................................................................12-30

12.16.5 Miscellaneous Items........................................................................12-30


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12. CONSTRUCTION METHODOLOGY AND EQUIPMENT PLANNING

12.1 Introduction

This section deals with the construction methods and implementation planning proposed

for the main components of Gongri Hydroelectric Project. The construction methodology

for each type of structure is described under the relevant sub-sections of this chapter. The

type and size of equipment to be used is indicated while describing the construction

methodology. The number of machines required for construction of the project and total

requirement for each type and size of the major equipment is worked out. It is aimed to

have least possible variety of equipment, yet a project of such a magnitude does need

several different types of equipment to cater to the progress rates as required by the

construction schedule.

It is appreciated that the contractors in all probability may suggest their own construction

techniques and equipment for execution of the job based on equipment actually available

with them. However, the present exercise will help in evaluating the reasonableness of the

bids and construction method and cost estimate.

12.2 Basis for Study

The construction cost and time depend to a great extent on the method adopted to carry

out the work and equipment deployed for the same. As there are alternative

methods/equipment, due care has to be exercised in selection of most efficient

construction method/equipment so as to optimize construction cost and time. These two

factors are inter-related and generally, any attempt to reduce one results in increasing the

other. Therefore, a balance has to be maintained and construction cost and construction

period are to be optimized after comparative evaluation of price escalation and interest

during construction versus lost benefits due to delay in completion.

12.2.1 Major Components

Gongri hydroelectric project involves construction of a 40 m long Barrage across river

Gongri with pondage required for peaking. The regulated releases from the reservoir would

be led to a surface powerhouse having an installed capacity of 90 MW (3X30 MW) and

thereafter will be discharged back into the river the water conductor system comprises:

• A Barrage with Intake

• 2 Nos. De-silting Basins with Feeder and Link Tunnels

• 4.7m dia finished Horse shoe-shaped Head Race Tunnel about 7.75 km long,


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• An 10 m Dia underground Surge Shaft open to sky,

• A 3.5 m dia steel lined pressure shaft with three 2.0 m Dia penstock branches off

taking from it for feeding the turbines,

• Surface Powerhouse with three Francis type Units of 30 MW each, and

• A tail race connected with the river.

12.2.2 Material Sources

Detailed construction material survey has been carried out as part of geotechnical survey.

Sufficient quantity of material to be used as coarse aggregate in concrete is available

within reasonable distance of the project works. Aggregate crushing and processing plants

will be installed at a suitable locations. Suitable sand for use as fine aggregate is not

available in the vicinity. Crushed sand is therefore proposed to be used. Areas for disposal

of excavated material from various works have been identified for equipment planning

purposes. Locations of Quarries, Aggregate Plants, Batching and Mixing Plants, Dumping

areas have been identified and their distances from various project components to

determine the lead to be taken for working out unit rate of civil work items and equipment

planning has been worked out and are detailed in Annexure-12-5.

12.3 Basic Considerations

Mechanized construction has been planned for almost all types of construction activities so

as to achieve consistent quality at a faster progress rate. The sequencing of construction

activities, wherever possible, has been attempted in such a way that equipment from one

activity, on its completion can be shifted to the other. This way the total requirement of

equipment at a time would be reduced and also, sufficient utilization of equipment on the

project would be ensured.

12.3.1 Number and Type of Construction Contracts, Basic Hypothesis

All main civil works can suitably be divided into optimum number of contract packages,

considering that the works are to be executed through award of contracts and duly taking

into the consideration the capabilities of prospective and eligible contractors. Supply and

erection of penstocks and other hydro-mechanical components like intake and barrage

gates, etc. will, however, be part of the civil contracts so that the problem of interface

between civil and hydro-mechanical works are minimized and the schedule be adhered to

meticulously. While deciding the optimum number of contracts for civil works, it is to be


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ensured that interference between different work areas is minimal and sufficient space is

available for different contractors’ camps and construction facilities.

The work for construction of accesses and the basic site infrastructure will have to be

taken up in advance so that the same are available by the time main civil contractor(s)

start mobilizing for their respective work.

12.3.2 Scheduled Working Hours

Equipment planning for calculating requirement of equipment is carried out based on the

number of working days available, which depends upon climatic conditions in the project

area. In the project area, a working season of 8 months will be possible after allowing for

monsoon season of 4 months. The scheduled working hours considering 25 working days

per month accordingly work out as under:

Single shift work/day =8x25x6 =1200 hours

Two shift work/day =8x25x11 =2200 hours

Three shift work/day =8x25x15 =3000 hours

Since the production capability would be affected during monsoon months especially for

the supplies/services and muck disposal, etc., suitable reduction in the progress has been

taken into account for the year as a whole.

Planning for all above ground and under ground works has been done for three shifts

working.

Provision of stand by equipment has been considered as follows:

• Single shift working 10%

• Two shift working 20%

• Three shift working 30%

Production rates for various types of excavation and dozing equipments used for

determining their requirement is given in Annexure 12-A.

The requirement of 10T tippers / 15T dumpers with 1 cum capacity Excavator / 1.15 cum

capacity loader for various leads have also been worked out and are given in

Annexure 12-B.

The requirement of 3 / 4 Cum Transit Mixers with 25 & 10 Cum/hrs capacity concrete

pumps for various leads have also been worked out and are given in Annexure 12-C.


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12.4 Construction Schedule

It is proposed to complete the project and commission all the three units in a period of

48 months from the date of start of the project. Construction of all the works shall be taken

up simultaneously in such a manner so as to complete the works in a period of 44 months

allowing a period of one month for initial filling and testing of the water conductor system

and commissioning and testing of the units at an interval of one month thereafter. Based

on the equipment planning and construction programme described in the succeeding

sections, a construction schedule for the project has been prepared in the form of a bar

chart and is attached as Annexure 12-1.

12.5 Preconstruction Activities

It is presumed that the execution of the project shall start with effect from the month of

October of the year of start of execution (Taken as zero month). All administrative,

financial and legal formalities for execution of the project need to be completed by this

time. It is necessary that all infrastructural works as mentioned below are completed before

zero month so that construction of main works is started on schedule:

• Acquisition of land required for construction of structures, bridges and roads, project

colonies, stores, workshops, muck disposal area, quarry area etc

• Up-gradation and construction of access roads :

· Roads to Adit to bottom of Surge Shaft/downstream end of HRT, intermediate

Adits and barrage site;

· Approach road to Power House and Tail Race,

· Approach road to quarry site,

· Approach roads to muck disposal areas,

· Approach road to explosive magazines

• Areas for Aggregate and Batching and Mixing plants, Workshop and offices,

• Availability of construction power at Barrage, Power House, Intermediate Adit sites,

Pressure Shaft Site (i.e., downstream end of HRT), top of Surge Shaft and Colony,

batching and mixing plants areas, Aggregate Plant areas and workshop sites;

• Construction of residential and non-residential buildings, stores etc as per requirement.

The activities to take up infrastructural works shall be started about a year before zero

month so as to ensure that all such works are completed before the scheduled date of start


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of construction of the main civil works of the project. Some of these activities will continue

for some time during the 1st year of construction also. Special attention would be paid to

the early completion of main access roads and bridges.

12.6 Tender and Contracts

The contract for various packages shall be finalized in advance of the starting of the work

at site. All contracts for infrastructural development works shall be finalized 8 months

before starting month of execution (i.e. “Zero” month) to ensure the completion of all such

works before the start of the main civil works. All contracts relating to the civil works shall

be finalized at least 3 months before starting month of execution and order for

manufacturing and supply relating to electro-mechanical equipment shall be finalized in all

respects by “Zero” month.

Procurement of plant and machinery required for construction of the project will have to be

done by the civil construction agency by “zero” month

12.7 Material Sources

Based on preliminary investigations, suitable material for use as coarse aggregates in

concrete has been found to be available in sufficient quantity within reasonable distance of

the project works. Suitable sand for use as fine aggregate is, however, not available in the

vicinity. Crushed sand is therefore, proposed to be used.

Areas for disposal of excavated material from various works have been identified for

equipment planning purposes. Locations of Quarries, Aggregate Plants, Batching and

Mixing Plants, Dumping areas have been identified and shown on drawing giving

infrastructure details. Their distances from various project components to determine the

lead to be taken for working out unit rate of civil work items and equipment planning has

been worked out and are detailed in Annexure-12.5.

Batching & Mixing Plants and Aggregate Processing Plants proposed to be provided on

the project at the following locations:

A. Batching and Mixing Plants

1. A 60 cum capacity BM plant to meet the concrete requirements of:

- Barrage and Intake

- Feeder and Link tunnels

- De-silting Chambers


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- Gate Shaft, Gate Chamber and Inspection Adit

- Silting Flushing Tunnel

- Head Race Tunnel –upstream portion from Adit-1


- Head Race Tunnel –Intermediate portion from Adits-2 and 3


- Head Race Tunnel –Downstream portion from Adit-4

- Surge Shaft

- Pressure Shaft

- Powerhouse complex

- Switch Yard

B. Aggregate Crushing and Processing Plant

Aggregate Crushing and Processing Plants (120 TPH capacity each) one near the Barrage

area and another opposite Adit -3 on the right bank to meet the aggregate and sand

requirements of the project.

The capacities of the proposed B&M and Aggregate Processing and Crushing Plants have

been worked out as per details given in Annexure 12-3 and 12-4.

Equipment required for production of aggregates (coarse aggregates of different sizes and

crushed sand) are given in Table-12.1


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Table 12.1: Equipment Required for Production of Aggregates and Concrete

Equipment Capacity Number Location

Loader 1.15 cum 3 One at rock quarry site and one each at Aggregate Processing plants

Excavator 1.0 Cum 2 One each at R B quarry sites

Jack Hammers 120 cfm 5 At Rock quarry site

Pusher Leg 2 At Rock quarry site

Dozer 90 HP 1 At rock quarry site

Dumpers 15 T 3 To carry blasted boulders to crushing plant

Tippers 10 T 3 To carry aggregates from crushing plant to BM plant

Portable Compressors (Diesel)

171 cfm 2 For R B quarries

500 cfm 1 For rock quarry

BM Plants 60 cum/hr 1 Near Barrage area

30 cum/hr 2 1 opposite Adit-3 on right bank and another in Powerhouse complex

Aggregate crushing and processing plants

120 TPH 2 1 opposite Adit-3 on right bank and another in Barrage area

Blasting Accessories 3 sets 1 for rock quarry site and 1 each R B quarries

12.8 Barrage & Intake: Construction Methods & Equipment

12.8.1 Surface Excavation

For the construction of Barrage, the river diversion shall be done in half portion of the river

at a time by erecting temporary diversion. The diversion dyke will be designed in such a

way to pass the diversion flood. The floods shall be allowed to pass over the barrage

structure during the monsoon periods and no work on the Barrage shall be done during the

monsoons.

The surface excavation for Barrage involves common excavation and rock excavation.

Excavation work of the barrage is proposed to be carried out in conjunction with concreting

work. A period of 24 months has been earmarked for this activity. Work of barrage will be

executed in two parts- first the right half will be taken up and the water diverted to pass

through the left half portion by constructing a suitable diversion dyke as already


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mentioned. The construction work in the left half will be carried out in a similar manner

thereafter. The work of Intake structure is proposed to be carried out concurrently with the

left side portion of the barrage.

The quantity of excavation as estimated and capacity, for which provision of equipment for

the surface excavation is made, are given in Table 12.2

The hourly quantity of Surface Excavation in Table 12.2

Items Soil/Over Burden

Rock Remarks

Total Volume of excavation in Barrage & Intake

115185 cum

11470 cum

Working Time Period 10 months

Shift Proposed Three

Total Operational Hours 4125 Hours

Volume to be handled/ hr (In situ) 27.9 2.78

Volume to be handled/ hr (In situ) with 20% peak

33.48 3.33

Volume to be handled/ hr (Loose) 44.64 4.97 Swell Factor: 0.75 for Common Excavation 0.67 for Rock Excavation

Total Quantity to be handled /hr at a time

49.61 cum 1 hydraulic excavators of 1 cum capacity to be deployed

Following construction methods are proposed for surface excavations:

• Excavation and loading of excavated material by 1 cum. Hydraulic excavator.

• For rock excavation, requiring drilling and blasting, drilling the holes with hand-held

rigs/crawler rigs with suitable hole pattern.

• Transportation to the disposal areas by 10 T Tippers – 5 Nos.

• A 90 HP bulldozer is also required to stay in the disposal area for performing the rough

spreading of the unloaded material.


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12.8.2 Concreting: Construction Methods and Equipment

The total quantity of concreting involved and hourly pouring rate are indicated in Table 12.3.

Item Right side

Left side

Placement Quantity 26500 Cum

45600 Cum

Working Time Period 10 months

11 months

Shifts Proposed Three

Three

No of days in a month for Concrete placement

20 20

Operational hours/day 15 hrs 15 hrs

Total Operational hours 3000 hrs 3300 hrs

Volume of concreting /hour 9 cum 14 cum

The quantity of concrete required to be placed per day during the placement period is

presented in Annexure-12-3. The number of concrete pumps and transit mixers required to

meet the above placement rate are detailed in Annexure12-6. Following construction

method and equipment have been considered for concreting of Barrage and Intake:

• Placing of concrete will be done with the help of chutes and with concrete pumps

wherever necessary. For placement of concrete 2 nos. concrete pumps of 25 cum.

capacity each will be deployed.

• Concrete transportation by 4 cum. Transit mixers to the concrete pumps – Required 2

nos.

• Batching and Mixing Plant of capacity 60 cum/hr located within a radius of 1000

meters from the barrage. The practical output of the plant is generally about 60% of

theoretical capacity will be able to meet the peak hourly placement rate of barrage as

well as the requirement of intake, De-silting basins and a part of HRT.(For details refer

Annexure-12-4).

• An aggregate crushing and screening plant of 120 TPH for preparation of coarse and

fine aggregates to cater to the requirement of the Barrage Area (For details refer

Annexure-12-4).

• At RBM quarry, excavation of riverbed material by 1cum hydraulic excavator and

transportation to the aggregate processing plant by 10 T Tippers (For details refer

Annexure-12-B).


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Alternatively concreting of the Barrage can be done with the help of Tower Crane.

Major Construction Plant, Equipment required for construction is listed in Table 12.4

Equipment Capacity Number

Hydraulic Excavator 1 cum 1

JCB 1

Crawler Dozer 90 HP 1

Crawler/Wagon Drills 1

Jack Hammers 120 cfm 8

Concrete pumps 25 cum./hr 2

Transit Mixers 4 cum capacity 2

Tippers 10 T 5

Trucks 10 T 2

Dewatering Pumps of sort 6

Compressors 500 cfm 2

12.8.3 Construction Programme

Excavation of components would start in the 3rd month of year 1 and end by the 31st

month. Placement of concrete would start in the 2nd quarter of the year 1 and end by the

fortieth month.

• Barrage and Intake

The work of Barrage-Spillway shall be carried out as under

• Excavation of abutment and Barrage (Right Side) & construction of Diversion Dyke

• Restoration of Dyke

Month 3 – Month 8

Month 13 – Month 13

Concreting of Barrage and stilling basin in -Right half portion


• Construction of diversion dyke for taking up left side portion of barrage

• Restoration of Dyke



Excavation of barrage and stilling basin in the river bed – left side portion


Concreting of Barrage and stilling basin in -Left half portion

Month 28- Month 40


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Radial Gate erection

• Right 2 Radial gates

• Left 3 Radial gates

• Intake HM works

Month 16 – Month20

Month 37 – Month 42 Month 39 – Month 44

Testing of Radial Gates operation

• Right 2 Gates

• Left 3 barrage gates

Month 19 – Month20


12.9 Feeder and Link Tunnels

12.9.1 Excavation

The work of Feeder and Link Tunnels will be started immediately on start of execution of

the project. To start with, a ramp will be constructed to approach the Feeder Tunnels

portal. Small ring bund will be constructed on the left bank opposite the portal portion if

required. Before taking up the actual tunnel excavation, portal construction and slope

stabilization would be required for which the following sequence may be followed:

• Common excavations, that is, earth and boulders in overburden, to be excavated with

1 cum hydraulic excavator.

• Excavation in rock will be done by drilling and blasting for which track drill/jack

hammers are proposed to be used.

• Disposal of excavated material in both cases shall be done with 1 cum hydraulic

excavator and 10 T Tipper combinations.



• Slope stabilization to be done by using shotcrete machine and anchoring by hydraulic

drill rig.

• Portal concreting by using transit concrete mixers

The two Feeder tunnels are 3.5mx4.25m modified D-shaped finished size, about 680 m

long combined. Same size has been adopted for Link tunnels with a combined length of

about 250.0 m. The minimum excavated size of the tunnels shall be 4.5m x 5.25 m to

account for 300 mm thick concrete lining, 50 mm thick shotcrete and pay line margin of

about 150 mm. In view of the size of the Tunnels, excavation can be undertaken by full

face drill and blasting method.

The excavation is based on the following construction methods:


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• Drilling of the charge holes by means of two boom hydraulic drill jumbos equipped with

man basket.

• Driving of each round according to the class of rock (approx. 2.50 m for good to fair

rock and less for poor rock and multi drift method for tunneling in soft rock).

• Number of holes per round (including those necessary for carrying out smooth blasting

along the peripheral surface and vent holes) ranging from 35-40 according to rock

characteristics.

• Charging operation of explosive executed by means of man basket and firing of the

rounds nonel detonators.

• Loading of the muck resulting from blasting, by 1.15 cum wheel loader.

• Transport of the muck to the spoil area by 10T Tippers



• Shotcrete with the help of 10 cum capacity shotcrete machine with robo arm.

• Rock-bolting by fully mechanized Rock-bolting drilling rig.

With the above construction method and equipment, it will be possible to complete a cycle

of operation for heading within a period of 12 hours. Although the time of each activity

within a cycle may vary according to class of rock encountered, the total time cycle for the

pull planned as indicated above is likely to be of the same order. A typical cycle for fair

rock is given in Table 12.5 Equipments provided for excavation is as per the details given

in rate analysis for Feeder Tunnels.

Estimated Cycle Time Table 12– 5

Description of Job Good Rock Fair Rock Poor Rock

Pull = 2 m Pull = 1.5 m Pull = 1 m

% Rock Classification 10% 60% 30%

Pre-grouting/fore poling Nil Nil 5.0 hrs

Preparation for the job & profile marking 0.50 hr 0.50 hr 0.50 hr

Drilling of holes 1.00 hrs 1.00 hrs 1.00 hr

Charging & Blasting 1.50 hr 1.50 hr 1.00 hr

De-fuming 1.00 hr 1.00 hr 1.00 hr


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Mucking 1.50 hrs 1.50 hrs 1.25 hrs

Scaling and bottom cleaning 1.00 hr 1.00 hrs 1.00

Shotcreting and rock bolting 2.50 hr 3.00 hrs Nil

Providing Ribs and Lagging Nil Nil 4.00 hrs

Back filling Nil Nil 3.00 hrs

Total 9.00 hrs 9.50 hrs 17.75 hrs

Say 12 Hrs Say 12 Hrs Say 24 Hrs

Rate of progress per month

(with 25 days working time)

100.0 m 75.0 m 25.0m

With this cycle time, an average sustainable progress of about 60 m per month can be

achieved for excavation.

Following sequence of operation will be followed for concrete lining of the Feeder Tunnels:

• Concrete to be placed in three stages viz., kerb, overt and invert.

• Kerb concreting to be placed with the help of 20 m form work.

• Installation of rails on kerb for the movement of 12 m traveling formwork for overt

concreting.

• Pouring of concrete for overt by 25 cum/hr capacity concrete pump.

• Transportation of concrete by 4 cum capacity transit mixers.

• Installation of traveling formwork for invert.

• Pouring of concrete for invert with similar equipment as deployed for overt.

A typical cycle time for overt concreting is as under:

Table-12.6 Estimated Cycle Time in Overt Concreting (12 m)

Erection time 8.0 hrs

Pouring time 8.0 hrs

Setting time 24.0 hrs

Total 40.0 hrs

With cycle time of 40 hrs and 1 set of shutter form, an average progress of 6 m per day or

about 150 m per month can be achieved. With the deployment of 1 shutter, the lining of

both the Feeder Tunnels will be completed in 5 months. (Invert concreting will follow with a

lag of 1 month)


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Based on the above methodology, the work of Feeder Tunnels shall be carried out as

under.

Approach ramp and portal const. Month 1 – Month 3

Excavation –Feeder Tunnels 1& 2 Month 3 – Month 8

Excavation –Link Tunnels 1& 2 Month 7 – Month 15

Concreting of – Feeder Tunnel 1 - Feeder Tunnel 2

Month 37-Month 39 Month 40-Month 42

Concreting of – Link Tunnel 1 - Link Tunnel 2

Month 29-Month 30 Month 31-Month 3

Grouting and cleaning Month 40 – Month 44

12.10 De-Silting Basins

As a part of the water conductor system, two de-silting basins have been proposed. Each

De-silting basin is 9m (W) x13.8(H) x215m Long.

12.10.1 Construction Method and Equipment

A construction Adit to approach the downstream ends of the de-silting basins has been

planned to facilitate construction of de-silting basins. Another Adit will be taken off from this

Adit to the bottom of the de-silting basins. After the completion of construction Adit,

excavation of de-silting basins will be undertaken through that Adit, to be executed

simultaneously. The equipments available after excavation of Feeder Tunnels shall be

used for this activity to the extent available.

First of all, a tunnel of 6m D-shaped will be excavated through the crown portion of each

de-silting basin. This tunnel will be widened to form the crown portion of the basin. A 3.0m

x 4.5m pilot hole will be excavated from the floor of the De-silting basin excavated crown

portion up to the bottom Adit.

The construction method and type of equipment for the construction of crown portion is

similar to the construction of HRT. Thereafter, benching operation will be started by

dividing the chambers into segments and undertaking excavation of the segments. A

typical cycle for benching operation is given in Table 12.7


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Estimated Cycle Time for 10.5mx3.0mx3.0 m bench Table 12.7

Drilling of holes 4.00 hrs

Charging & Blasting 1.00 hr

De-fuming 0.50 hr

Mucking and cleaning 3.00 hrs

Scaling and bottom cleaning 0.50 hr

Rock-bolting & shotcreting 2.50 hrs

Total 11.50 hrs say 12 hrs

The construction methods and equipment for excavation of de-silting basins are as follows:

• Driving the tunnel through crown portion of de-silting basins by full face drill and blast

method deploying 2 boom drill jumbo for drilling and 1.15 cum hydraulic loader in

combination with 10 T Tippers for mucking. One 1.15 cum hydraulic loader, one 90 HP

dozer and two 10T capacity tippers will be required.

• Side walls slashing of the tunnel to form crown of the de-silting basins with the same

set of equipment.

• 3.0m x 4.5m size pilot holes will be excavated from the floor of the de-silting basin

crown portion to reach the bottom Adit.

• Excavation of benches of size 10.5m (W)x3m (Deep)x 3.0m (length) by deploying

crawler drill / jack hammers for drilling and 90 HP dozer for pushing the muck down the

pilot hole.

• Muck will be removed from the bottom Adit by loading in 10 T Tippers with the help of

1.15 cum wheel loaders. Two tippers will be required for mucking. (Refer annexure 12-

B)

• Concreting of the crown portion of the basins is proposed to be done with the help of

gantry after bench excavation up to 3 m depth, as erection of gantry after complete

excavation of the basins will be difficult. However, concreting may be done only in the

crown portion leaving a clear gap of about 3m so as to ensure that no damage to

concrete takes place during further blasting.

• After concreting the crown of the basins, excavation of the basins will be completed by

benching and removing the excavated material through the bottom Adit.


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• Concreting of the walls of the basins will be done thereafter with the help of concrete

pumps and usual wall formwork panels.

List of Major Construction Plant & Equipment Table 12.8


Two Boom Hydraulic Drill Jumbo 2

Wheel Loader 1.15 cum. 2

Crawler /Wagon Drill 2


Tippers 10T 6


Shotcrete Machine with Robot Arm 10 cum. 2

Shotcrete Machine 5 cum 2

Transit Mixers 4 cum 3

Traveler Form 12 m length 2

Hydraulic platform/Truck Jumbo 2

Shutter vibrator 12


Blasting Accessories 2

Welding sets 2

Concrete Pump 25 cum/hr 3

B & M Plant 60 cum/hr 1

Aggregate Processing Plant 120 TPH 1

Concrete Mixers 14/10 cft 2

Air Compressor 500 cfm 2

Grout Pump 2

Trucks 10 T 3


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12.10.2 Construction Program

The work of De-silting Basins shall be carried out as under

Excavation of Adit-1(A3) to Flushing Tunnel. Month 1 – Month 5

Excavation of crown portion of de-silting basins Month 7 – Month16

Excavation of 3.0m x 4.5m pilot shaft Month 19 – Month 19

Excavation of basins 1st bench (3m deep) Month 16– Month 20

Concreting of crown portion and transition Month 19 – Month 25

Excavation of basins incl bottom hoppers Month 26 – Month 32

Concreting of De-silting Basins Month 37 – Month 44

Excavation of gate gallery including adit Month 24 – Month 37

Concreting of gate portion of gate gallery Month 38 – Month 43

Erection of gates Month 41 – Month 43

Excavation of Flushing Tunnel Month 6 – Month 20

Concreting of flushing tunnel Month 25 – Month 39

Grouting and cleaning Month 38 – Month 44

12.11 Head Race Tunnel

The water conductor system includes a 4.7 m diameter modified horse shoe shaped

headrace tunnel of about 7.75 km length. The construction of HRT is proposed to be taken

up from four Adits. The Adit constructed downstream of the De-silting basins will also cater

to HRT excavation. Another face for excavation of the tunnel will be from an Adit to be

constructed upstream of surge shaft to approach downstream end of the tunnel. A branch

of this Adit will approach bottom of surge shaft. Two more intermediate Adits at about RD

3157.0 m and RD 5728.0 m from the upstream will be constructed. Thus the tunnel will be

excavated from 6 faces with maximum length of about 1300 m excavation from one face.

12.11.1 Construction Method & Equipment

Before taking up tunnel excavation, portal construction and slope stabilization at the Adits

would be required for which following construction sequence is suggested:

• Common excavation, that is, earth and boulder in overburden, to be excavated with 1

cum. hydraulic excavator.


167116-0000-40ER-0010-00 12-18

• Excavation in rock will be done by drilling and blasting for which track drills/heavy duty

jack hammers are proposed to be used.

• Disposal of excavated material in both cases shall be done with 1 cum hydraulic

excavator and 10 T Tippers combination.



• Slope stabilization using shotcrete machine and anchoring by hydraulic drill rig

• Portal concrete by using portable concrete mixers with weigh batchers.

For a finished 4.7m diameter modified horseshoe shaped tunnel, the minimum excavated

size of the tunnel shall be 5.7m (to account for 300 mm thick concrete lining, 50 mm thick

shotcrete and a pay line margin of about 150 mm). In view of the size of the HRT,

excavation can be undertaken by full face drill and blasting method.

The excavation is based on the following construction methods:

• Drilling of the charge holes by means of two boom hydraulic drill jumbos equipped with

man basket.

• Driving of each round according to the class of rock (approx. 2.00 m for good to fair

rock and less for poor rock and multi drift method for tunneling in soft rock).

• Number of holes per round (including those necessary for carrying out smooth blasting

along the peripheral surface and vent holes) ranging from 40-50 according to rock

characteristics.

• Charging operation of explosive executed by means of man basket and firing of the

rounds nonel detonators.

• Loading of the muck resulting from blasting, by 1.15 cum wheel loader.

• Transport of the muck to the spoil area by 10T Tippers

• Shotcrete with the help of 10 cum capacity shotcrete machine with robot arm.

• Rock-bolting by fully mechanized Rock-bolting drilling rig/with the help of two boom

hydraulic drill jumbo.

With the above construction method and equipment, it will be possible to complete a cycle

of operation for heading within a period of 12 hours. Although the time of each activity

within a cycle may vary according to class of rock encountered, the total time cycle for the


167116-0000-40ER-0010-00 12-19

pull planned as indicated above is likely to be of the same order. A typical cycle for

different rock condition is given in Table 12.9

Estimated Cycle Time (Hrs) Table 12.9

Description of Job Good Rock Fair Rock Poor Rock

Pull = 2.0 m Pull = 1.5 m Pull = 1.0 m

% Rock Classification 10% 50% 40%

Pre grouting/fore poling Nil Nil 5.0 hrs

Preparation for the job & profile 0.50 hr 0.50 hr 0.50 hr

Drilling of holes 1.50 hrs 1.25 hrs 1.00 hr

Charging & Blasting 1.00 hr 1.00 hr 1.00 hr

De-fuming 1.50 hr 1.50 hr 1.00 hr

Mucking 2.50 hrs 2.00 hrs 2.00 hrs

Scaling and bottom cleaning 1.00 hr 1.00 hrs 1.00hr

Shotcreting and rock bolting 2.00 hr 3.50 hrs Nil

Providing Ribs and Lagging Nil Nil 3.50 hrs

Back filling Nil Nil 3.00 hrs

Total 10.00 hrs 10.75 hrs 18.00 hrs

Say 12 Hrs Say 12 Hrs Say 24 Hrs

Rate of progress per month

(with 25 days working time)

100.0 m 75.0 m 25.0m

With this cycle time, an average sustainable progress of about 57.5 m per month can be

achieved for excavation of HRT. Equipments provided for excavation is as per the details

given in rate analysis for HRT excavation.

A note on Method of tunneling in soft rock is attached at Annexure 12-8

Following sequence of operation will be followed for concrete lining of the HRT:

• Concrete to be placed in three stages viz., kerb, overt and invert.

• Kerb concreting to be placed with the help of 20 m form work.

• Installation of rails on kerb for the movement of 12 m traveling formwork (collapsible

shutters) for overt concreting.

• Pouring of concrete for overt by 25 cum/hr capacity concrete pump.


167116-0000-40ER-0010-00 12-20

• Transportation of concrete by 4 cum capacity transit mixers.

• Installation of traveling formwork for invert.

• Pouring of concrete for invert with similar equipment as deployed for overt.

A typical cycle time for overt concreting is as under: Table 12.10

Estimated Cycle Time in Overt Concreting (12 m) Table 12.10

Erection time 8.0 hrs

Pouring time 8.0 hrs

Setting time 24.0 hrs

Total 40.0 hrs

With cycle time of 40 hrs and 1 set of shutter form, an average progress of 6 m per day or

about 150 m per month can be achieved. With the deployment of 6 shutters a progress of

900 m per month is likely to be achieved. Thus, the lining of HRT will be completed in 8-9

months. (Invert concreting will follow with a lag of 1 month)

Based on the above methodology, major construction plant and equipment required for

construction of HRT has been worked out as given in Table-12.11

List of Major Construction Plant & Equipment for Head Race Tunnel Table 12.11


Two Boom Hydraulic Drill Jumbo

4



Tipper 10T 16


Shotcrete Machine with Robo Arm 10 cum. 4


Transit Mixers 4 cum 12

Traveler Form 12 m length 6

Hydraulic platform/Truck Jumbo

4

Shutter vibrator

24


167116-0000-40ER-0010-00 12-21

Needle vibrator

12

Dewatering Pumps of sort

12

Blasting Accessories

6

Welding sets

6

Concrete Pump 25 cum/hr 6

B & M Plant 30 cum/hr 2

60 cum/hr 1

Aggregate Processing Plant 120 TPH 2

Concrete Mixers 14/10 cft 3

Concrete placer 6

Air Compressor 500 cfm 3

Grout Pump

4

Trucks 10 T 6


The sequence of construction of HRT takes into account the following aspects:

• Open excavation for portal construction is to be undertaken in the 1st quarter of year 1.

Completion of Adits in next 4 months.

• Tunnel excavation from all faces will be started immediately after the Adits have been

completed that is from 8th month of first year.

• Tunnel excavation from all headings will be completed by the quarter 2 of the year 3.

• Concrete lining of whole of HRT to be taken up from the four Adits with 6 sets of 12 m

long shutter forms at each location. Lining to start in quarter 3 of the year 3 and

completed by quarter 2 of the year 4.

• Grouting and cleaning of the HRT to start simultaneously with concreting with a lag of

about 3 months and completed 2 months after concreting.

12.12 Surge Shaft

An underground open to sky orifice type surge shaft of 10.0 m diameter and having a

height of about 75 m is a part of the water conductor system.


167116-0000-40ER-0010-00 12-22

12.12.1 Construction Method and Equipment

Considering the dimension of the shaft and ease of construction, the surge shaft is

proposed to be excavated in two stages. In the first stage a pilot shaft will be excavated

through the height and thereafter the shaft will be widened to the final size. Pilot shaft will

be excavated from top manually by usual drill and blast technique, drilling being done

manually by jackhammers. (Raise climber has not been considered in view of the activity is

not being critical) A winch-operated hoist will be used for lowering men and material and

lifting the muck with the help of a bucket of appropriate size. Simultaneously, excavation

will be taken up from the Adit provided at the downstream end of HRT to approach the

bottom of surge shaft. After the pilot hole is excavated up to the bottom chamber, widening

of the shaft to the final dimension will be undertaken by conventional drill and blast method

from top of the shaft. Men and material will be lowered from the top using winch operated

hoist. Widening operation will be taken up by excavating in 1.0 m lifts at a time.

The construction method for widening of the shaft is as under:

• Drilling of the charge holes by jackhammers after covering the pilot hole with a steel

baffle plate to ensure safety of the crew.

• Drilling length to be controlled to produce funnel profile to facilitate flow of blasted

material towards pilot shaft.

• Pushing of the remaining blasted material through pilot shaft manually or by JCB.

• Removal of muck at bottom of pilot shaft by deploying 1.15 cum loader with 10 T

Tipper.

• Rock bolting and shotcreting as per design parameters and field requirements and and

providing steel supports (Ribs).

A typical cycle of widening of Surge Shaft for a lift of 1.0 m is given in Table-12.12


167116-0000-40ER-0010-00 12-23

(A) Estimated Cycle Time for excavation of 1m Lift of Pilot Hole Table 12.12

Profile marking and setting of operation 1.0 hr

Drilling Time 4.0 hrs

Charging and blasting 2.0 hrs

De-fuming and clearing 1.0 hr

Scaling and bottom clearing 1.0 hr

Mucking and clearing 12.0 hrs

TOTAL 21.0 hrs

Say 24 hrs

(B) Estimated Cycle Time for excavation of Surge Shaft in 1.0 m Lift


Charging and blasting 2.0 hrs

De-fuming and clearing 1.0 hr

Scaling and bottom clearing 1.0 hr

Dozing time of muck in pilot hole 4.50 hrs

Rock-bolting 2.50 hrs

Shotcreting 2.0.0 hrs

Total 19.0 hrs

Say 24 hrs

With a cycle time of 24 hours for a lift of 1.0 m for widening of surge shaft, an average

monthly progress of about 12 to 15m can be achieved. Thus the widening of the surge

shaft will take about 6 months. However, this being not a critical activity a working period of

12 months has been provided in the schedule keeping in view the logistics of the location.

The time provided is in addition to 6 months provided for excavation of the pilot hole.

Equipments provided for excavation is as per the details given in rate analysis for Surge

Shaft Excavation.

Concreting of the surge shaft will be undertaken at the end. It will be carried out from

bottom to top. As the excavated diameter of the surge shaft is 11.5 m and it will be difficult

to handle a single shutter form of such a size, concreting is proposed to be done in two

segments. Alternatively, slip form can be used for surge shaft concreting.


167116-0000-40ER-0010-00 12-24

(C) Estimated Time Cycle for concreting of Surge Shaft in 1.5 m Lifts in 2 segments

Erection of reinforcement 16.0 hrs

Cleaning and Erection of shutter form 8.0 hrs

Concreting 4.0 hrs

Setting time 36.0 hr

Total 64.0 hrs

Say 72 hrs

Thus one lift of 1.5 m will be completed in 6 days. An average progress of 6 m per month

will be achieved. This being not a critical activity a period of 15 months has been provided.


The construction of Surge Shaft is scheduled as under:

Excavation of Pilot Hole Month 3– Month 8

Widening of Shaft Month 9 – Month 21

Concreting of Shaft Month 22 – Month 39

Grouting and cleanup Month 37 – Month 44

HM work Month 37 – Month 44

Based on the above methodology, major Construction Plant and Equipment required for

construction of Surge Shaft have been worked out as given in Table- 12.13

List of Major Construction Plant & Equipment for Surge Shaft Table 12.13



JCB/Back Hoe

1


Pusher legs

4

Tipper 10T 4


Dry Shotcrete Machine 5 cum 1

Transit Mixers 4 cum. 4

Concrete shutter form

2 sets

Concrete Pump 10 cum. 1

Grout Pump

1

Batching and mixing plant* cccum/hr

1


167116-0000-40ER-0010-00 12-25

Aggregate Processing Plant*

1

Trucks 10 T 2


4

Mobile Crane 20 T 1

Welding Sets

1

Needle vibrator

6

Electric Winch 10 T 1

Portable compressor 500 cfm 1

12.13 Pressure Shaft

For carrying out the work of pressure shaft independently, access is proposed to be

provided by taking off an Adit from Adit to downstream end of HRT. This will enable taking

up work of pressure shaft independent of the work in HRT.

The pressure shaft works comprise a 3.5 m dia shaft about 500 m long. Out of total length

of pressure shaft, first 35 m is horizontal, then 155 m is vertical and further 300 m again

horizontal. Thereafter it bifurcates into 3 branches of 2.0 m dia, having a total length of

about 150 m so as to feed 3 units in the power house.

12.13.1 Construction Method

The excavation of the top horizontal portion of pressure shafts will be carried out through

the Adit with full face drilling and blasting method. The construction methodology for

excavation of horizontal pressure shafts is similar to that adopted for HRT.

The excavation of vertical portion of the pressure shafts (about 155 m in height) will be

carried out from bottom using raise climber equipment. A construction Adit (Adit-5) will be

provided for approach to the bottom of pressure shafts and construction of horizontal

portion of pressure shafts.

Typical cycle of operation for excavation in the vertical pressure shaft with the use of

Alimak Raise Climber equipment is given below:

Estimated Cycle Time for excavation of Vertical Pressure Shaft 1m Lift/ cycle

Travel of Raise Climber to face 0.5 hr

Installation of rail/scaling and Rock-bolting 5.00 hrs

Profile marking 0.5 hr


Charging of holes 2.00 hr


167116-0000-40ER-0010-00 12-26

Descending of Raise Climber 0.5 hr

Blasting and De-fuming 2.50 hrs

Total 18.00 hrs

Say 24 hrs

The mucking cycle is out of time cycle and not critical. Equipments provided for excavation

is as per the details given in rate analysis for Pressure Shaft Excavation.

On completion of excavation, steel lining of the pressure shafts will be carried out.

Penstock installation shall proceed from inside to outside in horizontal portion whereas

from bottom to top in case of vertical shaft. Steel ferrules, 5m long fabricated in workshop

will be transported on a trailer and will be unloaded by a mobile crane/EOT crane and

lowered to the position of installation with the help of a winch and pulley arrangement,

aligned and welded. Finally the penstock ferrule will be buried in concrete after requisite

testing of the welded joint. The entire sequence of installation of a 5 m long penstock

assembly is likely to take about 5 days.

Based on the above methodology, major Construction Plant and Equipment required for

construction of Pressure Shaft have been worked out as given in Table- 12.14

List of Major Construction Plant & Equipment for Pressure Shaft Table 12.14


Two Boom Hydraulic Drill Jumbo

1

Alimak Raise Climber with 2 stopper drills

1



Tipper 10T 3





Grout Equipment

1

Air Hoist

1

Batching and mixing plant*

1

Aggregate Processing Plant*

1


167116-0000-40ER-0010-00 12-27

Trucks 10 T 2


4

Mobile Crane 20 T 1

Welding Sets

5

Flexi Shaft Needle Vibrators

6

Electric Triple drum Winch 10 T 1

Portable Air compressor 500 cfm 2

Blasting Accessories

2

Hydraulic Platform/Truck Jumbo

1


The construction programme for the construction of pressure shaft is as under:

Excavation of Pressure shaft Month 7 – Month 20

Installation of penstocks and concreting in vertical Shaft portion Month 19 – Month 42

Installation and concreting of penstocks branches PB1 , PB2 &

PB3


Grouting, plugging, final finishing Month 29 – Month 42

Adit plugging Month 43 – Month 44

12.14 Powerhouse Complex

A surface powerhouse complex comprising of Powerhouse, Transformer Deck, and

Tailrace have been provided. The plan area for excavation of the entire Powerhouse

complex is 65.3 m (L) x 18 m (W) x 37.3 m (H). About 107400 cum of Excavation for

Powerhouse complex is in overburden and 26900 cum in rock is envisaged.

A period of 8 working months has been earmarked for undertaking the proposed surface

excavation.

Common Excavation Rock Excavation

Total Volume of excavation 107400 cum. 26900 cum

Working Time Period 8 months 8 months


167116-0000-40ER-0010-00 12-28

Shifts proposed Three Three

Total operational hours 3000 hours 3000 hours

Volume to be handled/hour (in-situ) 36 cum 9 cum

Volume to be handled/hour (Loose) 48 cum 14 cum

Volume to be handled/hour (Loose) 62 cum

Following construction equipments are proposed for surface excavation:

• Excavation and loading of the material by 1 cum. Hydraulic excavators. For rock

excavation, requiring drilling and blasting, drilling the holes with hand-held rigs/crawler

rigs with suitable hole pattern.

• Transportation to the disposal areas by 15 T Tippers – 4 (Refer Annexure 12-B)



• Concreting of powerhouse complex will be done with 25 cum. concrete pumps and

transit mixers. A period of 30 months has been earmarked for entire concreting

including second stage concreting for E&M works.

12.14.1 Construction and Equipment

List of major Construction Plant and Equipment required for construction of Powerhouse

complex have been worked out as given in Table- 12.15

List of Major Construction Plant & Equipment for Power House Complex Table 12.15


Hydraulic Excavator 1 cum. 2



Tippers 15t 5

Dry shotcrete machine 6 Cum. 1



Grout Equipment 1


Mobile Crane 20 T 1


167116-0000-40ER-0010-00 12-29

Welding Sets 3

Flexi Shaft Needle Vibrators 8

Stationary Air Compressor 500 cfm 1

Portable Air compressor 500 cfm 1


Surface Excavation of Powerhouse Complex Month 1 – Month 12

Concreting: sub and super structure Month 13 – Month 42

12.14.3 Electro-Mechanical Equipment

Proposed schedule for design, supply, erection and commissioning of electro-mechanical

equipment is as follows:

Design Supply Erection

EOT 3 months 9 months 3 months

Transformer 3 months 9 months 3 months

Turbine & Generator

6 months 12 months 16 months

Switchyard - 12 months 6 months

12.15 Requirement of Construction Equipment

A comprehensive list of the major construction equipment and plants required for the

execution of the project component wise is given in Annexure 12-2.

12.16 Key Material Requirement/ Planning

Construction of the project would require large quantities of materials. Among the various

materials, the requirement of steel and concrete will be most predominant. Concrete

production will involve uses of cement, coarse and fine aggregates. In addition, large

quantity of explosives would also be required as the project components are almost all

underground.

12.16.1 Quantity of different materials

The quantities of the above materials, along with those of miscellaneous items, are given

in Table 12-16 and Annexure 12-7.


167116-0000-40ER-0010-00 12-30

Table 12-16: Construction Material Requirement

Particulars Unit Quantities

Required

Open Excavation m3 319485

Rock Excavation m3 480955

Cement MT 111820

Silica MT 178

Boulders m3 47542

Aggregate m3 197910

Sand m3 117632

Reinforcement Steel MT 3597

Structural Steel MT 3241

Rock Bolt (25 mm) m 120030

Gelatin Kg 411059

Detonators Nos 240502

Fuse Coil Nos 240502

Penstock Steel: ASTM 537 Gr.-II MT 1468

12.16.2 Coarse and Fine Aggregates

A thorough survey in and around the project area was undertaken to ensure availability,

suitability and mine-ability of the construction materials and to identify the potential source

of locations for the coarse aggregate (projected requirement 1,23,505 m3) and fine

aggregate (projected requirement 75,079 m3). Details of this survey are provided in

Construction Materials Survey report for Bop Hydro-Power Project.

12.16.3 Cement and Steel

Cement shall be procured from sale depot at Guwahati, and reinforcement steel and

structural steel from SAIL Stockyard at Guwahati.

12.16.4 Explosives

Explosives shall be obtained from authorized dealers and carried to the site from the

nearest retail magazine outlets.

12.16.5 Miscellaneous Items

Other materials like drill steel, diamond bits, welding rods, oil and lubricants etc. are

proposed to be obtained from the open markets.

Documents

Chapter 12