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Gongri Hydroelectric Project Feasibility Report
167116-0000-40ER-0010-00 i
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
12.9.2 Construction Programme.................................................................12-14
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
12.11.2 Construction Program......................................................................12-21
12.12 SURGE SHAFT..................................................................................................12-21
12.12.1 Construction Method and Equipment...............................................12-22
12.12.2 Construction Programme.................................................................12-24
12.13 PRESSURE SHAFT ............................................................................................12-25
12.13.1 Construction Method .......................................................................12-25
12.13.2 Construction Programme.................................................................12-27
12.14 POWERHOUSE COMPLEX ..................................................................................12-27
12.14.1 Construction and Equipment ...........................................................12-28
12.14.2 Construction Program......................................................................12-29
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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
2. A 30 cum capacity BM plant to meet the concrete requirements of:
- Head Race Tunnel –Intermediate portion from Adits-2 and 3
3. A 30 cum capacity BM plant to meet the concrete requirements of:
- 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
Month 4 – Month 15
• Construction of diversion dyke for taking up left side portion of barrage
• Restoration of Dyke
Month 25 – Month 26
Month 37 – Month 37
Excavation of barrage and stilling basin in the river bed – left side portion
Month 27 – Month 31
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
Month 43 – Month 44
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.
• A 90 HP bulldozer is also required to stay in the disposal area for performing the rough
spreading of the unloaded material.
• 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
• A 90 HP bulldozer is also required to stay in the disposal area for performing the rough
spreading of the unloaded material.
• 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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12.9.2 Construction Programme
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
Equipment Capacity Number
Two Boom Hydraulic Drill Jumbo 2
Wheel Loader 1.15 cum. 2
Crawler /Wagon Drill 2
Jack Hammers 120 cfm 12
Tippers 10T 6
Crawler Dozer 90 HP 2
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
Dewatering Pumps of sort 8
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.
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• 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.
• A 90 HP bulldozer is also required to stay in the disposal area for performing the rough
spreading of the unloaded material.
• 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
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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.
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• 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
Equipment Capacity Number
Two Boom Hydraulic Drill Jumbo
4
Wheel Loader 1.15 cum. 4
Jack Hammers 120 cfm 8
Tipper 10T 16
Crawler Dozer 90 HP 3
Shotcrete Machine with Robo Arm 10 cum. 4
Shotcrete Machine 5 cum 4
Transit Mixers 4 cum 12
Traveler Form 12 m length 6
Hydraulic platform/Truck Jumbo
4
Shutter vibrator
24
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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
12.11.2 Construction Program
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.
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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
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(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
Drilling Time 6.0 hrs
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.
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(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.
12.12.2 Construction Programme
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
Equipment Capacity Number
Wheel Loader 1.15 cum. 1
JCB/Back Hoe
1
Jack Hammers 120 cfm 8
Pusher legs
4
Tipper 10T 4
Crawler Dozer 90 HP 1
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
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Aggregate Processing Plant*
1
Trucks 10 T 2
Dewatering Pumps of sort
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
Drilling Time 7.00 hrs
Charging of holes 2.00 hr
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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
Equipment Capacity Number
Two Boom Hydraulic Drill Jumbo
1
Alimak Raise Climber with 2 stopper drills
1
Wheel Loader 1.15 cum. 1
Jack Hammers 120 cfm 3
Tipper 10T 3
Crawler Dozer 90 HP 2
Shotcrete Machine 5 cum 2
Transit Mixers 4 cum. 4
Concrete Pump 25 cum. 2
Grout Equipment
1
Air Hoist
1
Batching and mixing plant*
1
Aggregate Processing Plant*
1
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Trucks 10 T 2
Dewatering Pumps of sort
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
12.13.2 Construction Programme
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
Month 26 – Month 42
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
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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)
• A 90 HP bulldozer is also required to stay in the disposal area for performing the rough
spreading of the unloaded material.
• 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
Equipment Capacity Number
Hydraulic Excavator 1 cum. 2
Crawler Dozer 90 HP 1
Jack Hammers 120 cfm 8
Tippers 15t 5
Dry shotcrete machine 6 Cum. 1
Transit Mixers 4 cum. 3
Concrete Pump 25 cum. 2
Grout Equipment 1
Dewatering Pumps of sort 8
Mobile Crane 20 T 1
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Welding Sets 3
Flexi Shaft Needle Vibrators 8
Stationary Air Compressor 500 cfm 1
Portable Air compressor 500 cfm 1
12.14.2 Construction Program
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.
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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.