A dynamic stress state analysis at the pressure tunnel of Upper Tamakoshi HPP, Nepal

Abstract

In theory, in-situ stress state of an area of concern is mainly governed by gravity-induced stress, tectonic ac-tivity and topographic condition of that area. The tectonic and geological environment such as faulting and shearing in the rock mass greatly influences magnitude of the in-situ stress of area under investigation. The Himalaya is renowned with its active tectonic movement resulting periodic dynamic earthquakes, which caus-es accumulation and sudden release of strain energy instigating changes in the in-situ stress environment. This paper aims to evaluate the influence by local shear fault on in-situ stress state along shotcrete lined high pres-sure tunnel of Upper Tamakoshi Project, where considerable hydrostatic head will act on the rock mass. A de-tailed assessment of in-situ stress state is carried out by using both measured data and three-dimensional nu-merical analysis using FLAC3D. Furthermore, an attempt has been made to evaluate changes on in-situ stress state caused by seismic activities (dynamic loading).