Surge Shaft Instrumentation and Monitoring in Himalayan Hydroelectric Projects

Abstract

The main purpose of providing the surge shaft in hydropower projects is to absorb the water hammer. These shafts have larger diameter when compared to other type of shafts used in underground structures. Surge shafts also serve as a supply tank to the turbine when the water in the pipe is accelerating during increased load conditions and as storage tank when the water is decelerating during the reduced load conditions. The surge shafts may be of open to sky type or may be excavated under rock cover based on the topographical conditions.

Construction of these shafts are critical and expensive when weak geological conditions are encountered. Hence monitoring of these shafts using geotechnical instrumentation during construction will save construction time and cost. The general instrumentation that can be installed in shafts are to monitor displacements in rock around the opening using multipoint extensometers, convergence measurements with tape extensometers and total station, pore water pressure with piezometers, load on support elements using load cells. Based on the instrumentation data decisions can be taken for modification of support system, if required any. In this paper, two case studies related to the instrumentation monitoring of surge shafts in Himalayan region discussed. Numerical modelling studies were carried out using FLAC3D software for comparing the behaviour of the shafts with the instrumentation data.