INFLUENCE OF SEQUENCE OF EXCAVATION ON THE DEFORMATION BEHAVIOUR OF CAVERN

Abstract

A cavern is an important part of most of the hydroelectric projects. The construction of large caverns for powerhouses need prior knowledge of the stresses and deformations due to excavation. The underground excavation of rock mass at such a large scale causes the disturbance in primitive stress field. Because of disturbance in prevailing stress field, redistribution of stresses takes place and results in stress concentration around the boundary of the excavation. Since rocks near the excavation boundary have no restraints towards the excavated region, they tend to displace into the cavern. Overstressing and large deformations of rock mass may cause the failure of structure and thus impair the functional objective of the structure. Therefore, a proper analysis of deformations and stresses should be carried out to assess the extent of instabilities. In the present work, deformation behaviour of cavern has been studied due to sequential excavation using 2-D finite element method. The rock mass has been considered isotropic, homogeneous and linearly elastic. The analysis of Sardar Sarovar Powerhouse Cavern has been done. The SSP cavern is210m long, 23m wide and 58 m high. Deformation of cavern after every excavation of the cavern part has been obtained. The variation of horizontal and vertical stresses around powerhouse cavern has also been taken into account.