A chapter on HRT equipment in a 100MW hydro electric Project

By S. R Chowdhury & N. P Salhotra

Member (HPCS)

List of equipment and its planning

Q special T&P (provision of plants & equipment) in Cost estimate chapter of a HE Project is important because whenever we think about purchase of equipment for the construction, we require sufficient fund that should be available with us. The equipment provided in DPR and the methodologies always are not appropriate. Therefore we may change it where ever it is required, however it does not mean that I am criticizing their Planning in DPR or I would like to add a new chapter but I like some changes only which are beneficial to some organizations.  

Let us imagine that In DPR the provision of Q spl T&P in cost estimate has been kept as Rs.140 lakhs i.e.25% of total amount Rs.560 lakhs and in Receipt & Recoveries (-) Rs.140 lakhs that means the amount we are utilizing for Plant & equipment 25% will be back to our fund through disposal of equipment i.e. resale of old and used equipment as they are of no use to us after completion of the project and balance 75% shall be booked on civil works for construction of the project. 

Therefore whatever equipment is adding extra will increase or may decrease the above figure as we change certain things in equipment planning. 

Construction of a hydro electric project involves various activities like intake structure, Barrage, head race tunnel , surge shaft, pressure shaft, Power House, tail race tunnel or etc and from our past experience we know which activity is critical and how to tackle them with best type of equipment during excavation as well as concreting works. Each purpose there are two types of equipment one is under ground equipment and other is over ground equipment. Under ground equipment like Drill boom jumbo, rock bolters, small loaders, haulers/tippers, etc are used in Head race tunnel, under ground power house, surge shaft and pressure shaft etc and over ground equipment like Dozer, dumpers, excavators, loaders, motor grader etc are used in Dam/Barrage/weir, intake structure, power channel, desilting chamber, open power house etc. 

Equipment Planning

Before we go to purchase particular equipment from market, proper planning of equipment is required depending upon quantity of excavation and concreting i.e. BOQ and detail drawing of each component of the project, so that we may check the size and dimension of each component. Suppose we are going to plan equipment for a head race tunnel and in detail drawing it is mentioned that finished modified D shape of tunnel is w = 3.5 meter and H =3.375 +0.875 M therefore excavated size of the tunnel would be 0.5 meter more for concrete thickness along the periphery of the tunnel   that means we are going to select equipment which can go through a 4.0 meter tunnel easily and does not create smoke inside the tunnel there fore we may select electric or pneumatic equipment instead of diesel equipment but on the other hand the efficiency of diesel equipment is more. Keeping in view of the fact diesel equipment was planned in DPR and other disadvantages were not considered. As such we should choose the equipment which have better efficiency as well as does not create hindrances in our day to day work because from our past experience we have seen that in a Smokey tunnel the efficiency of man power is decreased and the progress becomes slow.   

According to me rail equipment is better and we should select the type of Loco to be used depending upon its pulling capacity, dragging force, efficiency etc and as per size of the tunnel 5 tone loco is most suitable for this purpose provided a good manufacturer of loco we are able to select. I know one of the manufacturers in the global market is available i.e.   Clayton Battery loco made in England is the best other than Indian manufacturers of any other. Though the Clayton battery loco is costly but the no of loco are required in lesser quantity than any other loco which may be required double the quantity. Thus we may be benefitted with Clayton Battery loco otherwise. 

Therefore when we are using loco & trolleys for mucking purpose (instead of diesel loader and tipper as per DPR) then the loader should be a rail bound equipment either electric or pneumatic type other than diesel . From our past experience we have seen the Eimco loader which has a good output and a rail bound loader driven by pneumatic pressure. This loader is giving full output and loads a 2 cum bucket in 5 minutes i.e. its loading capacity is 1 cum/ 2.5minutes. Now let us calculate the area of the tunnel considering 3.5 M width, H = 3.375+0.875 = 4.25 M, therefore the area of cross section is 21.12 sq.m as such no. of holes to be drilled = Area of the tunnel/(0.8*0.8) +4 = 37 no where 0.8m is the spacing of holes and so length of hole to be drilled = 37*1.5 = 55.5 M. So drilling time @ 40m/hr is 1.40 Hrs. as the drilling output of one boom drill jumbo is 50m/hr. and efficiency of machine has been considered as 80%. The Volume of muck per meter length would be = 21.12*1*1.6 = 33.8 cum. (1.6 is swell factor for loose muck). 

Therefore 33.8 cum muck has to be removed by a loader of 0.3 cum bucket capacity   at  40 cum/hr output, with 3no muck trolleys (with the help of California switch at heading) .Considering the above and lead distance 1.0 Km, we can calculate the cycle time in combination with loco and loader as below:- 

Therefore 3*2 = 6 cum muck is removing out within 23.0 minutes in one cycle, as such 33.8 cum muck shall be removed considering all delays due to operators management factors is approx. 2.5 Hours. 

In the same way we can also calculate the total excavation time as below:- 

Therefore we can achieve 2.0 M progress per day of 24 hours. The list of equipment to be used per face is as below:- 

1.       One boom drill jumbo – 1 no  

2.       5 ton Loco (Battery) – 2 no  

3.       Trolleys  2 cum– 6 no 

4.       Eimco Loader 0.3 cum -1 no 

5.       Jack hammer – 4 no 

6.       Transportation vehicle for ribs etc – 1no 

7.       ROC drilling equipment for fore polling -1 

8.       Ventilation duct & blowers 

9.       Welding set - 2 

10.   Dewatering pump – LS 

11.   Dozer 50 HP – 1 no 

12.   Pick & carry crane -1 no 

13.   Mechanical/Electrical work shop for repair and battery charging. 

Similarly we can calculate no of equipment for concreting in excavated portion after providing gantry of required length. Let us think the quantity of concrete required by calculation = Outer area – Inner area of the tunnel of finished diameter * length* void factor. The outer area is 25.0 sq.m and the inner area of tunnel of finished tunnel is 21.5 sq.m therefore qty of concrete required is 4.5 sq.m*5*1.1 = 25 cum concrete, where length of gantry is 5 meter and 10 % void factor has been considered. 

We can calculate cycle time for Concreting of the tunnel with a lead distance 1 KM:- 

 List of concreting equipments:

Therefore 10.0 M concreting of the tunnel may be done in one day of 24 Hour. The list of equipment to be used is as described below:- 

1.       Self crawled Gantry 5 m length - 6 no.

2.       Concrete pump 20 cum/hr capacity -3 no .

3.       B&M Plant 30 cum/hr - 2 no 

4.       Aggregate plant 40 TPH -1 no 

5.       Concrete vibrators – 12 no 

6.       Transit Mixer 2 cum -9 no 

7.       Transport vehicle for carriage of materials -1 no 

Conclusion:- 

In general hydro electric Project got delayed due to various types of difficulties during construction of Head race Tunnel. Therefore in small size tunnel it should always be chosen the construction equipment using for excavation should be easy to repair and convenient to use so that the breakdown time is minimized. 

Clayton Battery Loco 7tone 

Previously this type of Loco were used at Loktak HE Project under NHPC during 1980 successfully in 3.89 Diameter finished Size of HRT.

The above Eimco Rocker shovel is pneumatic drive suitable for mocking at 4.0 m width tunnel and using presently at BHPL Out let tunnel successfully and 350 cfm air is required to run this equipment.