Micro Seismic Monitoring for Analyzing Dynamic Stability of Underground Powerhouse Caverns in Himalayan Region

Abstract

Whenever rockmass is excavated underground for mines, tunnels, hydropower projects, newlineunderground storage chambers, underground metro railway works, etc., there is redistribution newlineof stresses around the openings. These additional redistributed stresses may render the newlineexcavation unstable with time if proper support measures are not adopted. During the last three newlinedecades, a number of hydroelectric projects have been constructed in the Himalayan region newlinewhich has a complex geological setting. Despite best design measures, the induced stresses in newlinethe rockmass around excavation create stability issues. newlineThe life and stability of underground rockmass structure depends on the long-term durability newlineand capability of the surrounding rocks to withstand induced stresses. This, in turn, depends on newlinestability of the support system around excavations i.e. static stability. Stability under both newlinetransient and gradual changes of the boundary conditions, i.e., dynamic stability is always a newlinetricky issue which poses challenges in the Himalayas. In this work, we have focused mainly on newlinethe deformation and stability brought out by the dynamics of induced seismicity due to newlineincreased stresses in the surrounding rockmass. newlineInduced seismicity consists of repeatedly occurring discrete seismic events of different newlinemagnitude and location. Though it is the duty of the design engineer to contain the induced newlinestresses by prescribing proper support measures for the excess stress build-up regions, failures newlinedo take place despite proper planning. Such failures had taken place in the underground newlinepowerhouses of Tapovan Vishnugad Hydro Power Plant and Tala Hydropower Plant (TVHPP newlineand THP), for which the microseismic monitoring network was established to delineate the newlinedynamics of induced seismicity leading to failure. newline