In situ stress measurement and its application for hydro-electric projects—an Indian experience in the Himalayas

Abstract

Any attempt to design engineering structures in rock mass requires knowledge of the prevailing in-situ stress field. It is always advisable to measure it, in whatever best way possible. The prior knowledge of the prevailing stress field helps in the alignment and the design of support system for the underground cavern, estimation of grouting pressure in the dam foundation, design of steel liners for Head Race Tunnel, Penstock, etc. There are various methods of determination of in-situ stresses in rock mass. However it has been experienced that the hydrofracturing technique is the most convenient to conduct and interpret the test results. This paper briefly describes the various uses of stress measurements, details of hydraulic fracturing test system, test procedure adopted and the concept of hydrofracturing in arriving at the in-situ stresses of the rock mass. The results for the above applications conducted at four mega hydroelectric projects in India and neighbouring countries of Bhutan and Nepal located in the Himalayas are presented.