Abstract :
A stress measurement program was undertaken at Punatsangchhu H.E. Project stage-I during January 2010 inside desilting chamber for the determination of in-situ stress tensor by hydro fracture method. This test was required to freeze the orientation of desilting chamber vis. a vis. orientation of maximum compression (ï³H) which was found to be N 150ï¯. The hydrofrac test was carried out at RD 100 and RD 150 inside an exploratory drift at dam-axis and approaching towards desilting chamber with a rock cover of 100 m. As it was only 100 to 150 m away from the portal a topography effect on the orientation of (ï³H) was not completely ruled out. So when the adit to desilting chamber reached at RD 360 with a rock cover of 410 m, it was necessary to carry out stress measurement to confirm the orientation of maximum compression (ï³H). The stress orientation as evaluated at RD 360m confirms the orientations revealed from earlier stress measurements at RD 100 and RD 150m.Thus it is recommended to freeze the direction of Desilting Chamber along N 150o. It also confirms that the earlier stress measurement results do not suffer from topography related influence.
Keyword :
Stress, Desilting chamber, Hydrofracture, Adit, Maximum compression, Topography