AKSHAY S KRISHNA

VNIT Nagpur

Sewa Hydroelectric Project (120 MW) is

located in Kathua district of Jammu and

Kashmir

J&K region is situated in foot-hills of

Himalayas where igneous rocks are abundant

Sewa river istributary to mighty Ravi River

The 53m high concrete gravity dam near

village Gatti aims at generating 120MW

electricityA 298 m long 6 m horse shoe

shaped concrete lined tunnel was

constructed for this HYDEL project

10.02km m long Head Race tunnel of 3.30m

Horse shoe including under ground pressure

tunnel-3nos with 2.4m in dia, 380m long and

vertical pressure shaft 622m with surface

penstock length of 175m and…

A diversion tunnel 6m dia and 298mm long

was constructed on right bank to facilitate

construction of Diversion Dam. Diversion

tunnel was designed to take even the flood

discharge

This tunnel though not very long in length

had typical design having two horizontal

bends.

Tunnel was passing through granite stone and

having seepage at various locations.

The tunnel was bored by conventional

drilling and blasting method by using full

face method.

SEWA PROJECT LAYOUT

Drilling activity was the most critical activity

since the rock encountered was very hard

and only one face was available for boring.

Consumption of drill rods was bit high

Drilling and blasting pattern asadopted is

shown in Fig

Blast hole drilling was initially planned by

drilling jumbo but later changed to high

speed jack hammers Atlas Copco make.

Actual penetration achieved on this rock was

0.25m/min.

Maximum pull in hard rock strata was

achieved 2.8m. It was decided not to drill

holes more than 10’ depth to avoid wastage

of time and money

Assumed average life of drill rod in tender

was 200m but actually achieved at site was

only 180m.

Grinding of drill rod was very important in

this type of rock.

Electric cup type grinder was used and

performance of this grinder found very

satisfactory.

To minimize the cost, rebitting of drill rod

was done locally and this experiment proved

very successful

Charging pattern was in accordance with the

wedge cut, drilling and blasting pattern

Modification in charging was that two

numbers primers were used in cut holes.

Due to hard rock, power factor was also

high. It was varying from 1 to 2 kg/m3.

Power gel 901 explosive with long delay

detonators were used

1. Survey and profile marking - 0.50 hours

2. Drilling - 2.00 hours

3. Charging & blasting - 1.00 hours

4. Defuming - 0.5 hours

5. Scaling/Mucking and

bottom cleaning - 4.5 hours

Rock support/Shotcreting - 2.5 hours

Total cycle time - 11.00 hours

Add for unforeseen - 1.00 hour

- 12.00 hours

Defuming system at this site was working all

right.

Sucking system ventilation was adopted and

proved to be effective.

Two units of 45kWx02, having dia .750mm

fans were installed at portal with 1000 mm

dia flexible duct