STABILITY ANALYSIS OF AN UNDERGROUND POWERHOUSE CAVERN

Abstract

Ever since the independence hydroelectric projects are being considered as the mo! conservative source of power generation. For this purpose powerhouse caverns are usuall constructed underground to increase the head available at the turbine level, without increasin the height of the dam, as the cost of height increment of the dam is much more than that c increasing the depth of the underground powerhouse cavern. Hence, the excavated undergroun~ cavities demand for an overall stability analysis of the surrounding rock mass, and a complet, understanding of the deformational behavior of loosened rock mass prior to the excavation o cavities. Whenever an underground excavation is created in such a rock mass, the re-distributioi of stresses takes place around the excavated cavity, with a very high stress concentration at the peripheral region of the cavity. The behaviour of underground caverns in massive competent rocks has been studied bi using theories of elasticity, plasticity and rheology. The surrounding rock mass is analyzed b} modeling its behaviour either physically, empirically or numerically, depending upon the site characteristics and also the importance of the project. Limitations of Physical modeling motivated the researchers go for different empirical approaches. With the negligence of the negligence of many site specific conditions in empirical methods and advancement in computing techniques, several numerical modeling approaches have been evolved. In this present study, a Hydro-Electric Powerhouse in Vishnugadh, Pipalkoti composed of three adjoining caverns has been analyzed using FLAC3D is a three-dimensional explicit finite-difference program for engineering mechanics computation. In FLAC3D, materials are represented by polyhedral elements within a three-dimensional grid that is adjusted by the user to fit the shape of the object to be modeled. Each element behaves according to a prescribed linear or nonlinear stress/strain law in response to applied forces or boundary restraints. Two different states of rock supports have been considered for excavation process. Analysis carried out using Mohr-Coulomb model for elastic isotropic rock properties. At first, the excavation processes are carried out without support in various sub-stages to predict the deformational behaviour and stress condition at different sub-stages of excavation. From this result an attempt has made to provide supports for multiple caverns and then checking its validity.