Engineering Geological Study On Caverns Of The Underground Powerhouse At Laxiwa Hydropower Station

The rich hydropower resources area in our country are mostly located in the the western deep valley region. Restricted by steep riverbank and narrow valley terrain conditions, the hydroelectric generator group was usually set in the underground cavern, the underground powerhouse with high sidewall and large span will inevitably encounter complex geological conditions and unpredictable engineering geological problems, among which the stability of surrounding rock is the biggest concern.In this paper, underground powerhouse cavern of the the Laxiwa Hydropower main plant and the main transformer room is taken for the example, the rock mass structure and strength characteristics are studied mainly from the engineering geological environment conditions, indoor test, in-situ testing, numerical analyses, theoretical methods and means, and the field stress formation mechanism and distribution characteristics are reproduced based on valley evolution process. On the basis of detailed site survey and testing, form basic geological conditions, fracture development characteristics, characteristics of the stress field, rock mass and cavern stability, the stability of surrounding rock for the cavern of underground main powerhouse and the main transformer room are studied.For Laxiwa hydropower station underground powerhouse cavern engineering geological studies, the main research topics include:(1) the regional geological environment and engineering geological conditions of the dam area;(2) the development characteristics and distribution law for occurrence of structural surface, degree of development, surface morphology of the plant area, drawing tendency node density figure;(3) using Q classification, RMR classification, hydropower specification standards to evaluate surrounding rock quality and rock mass quality space distribution characteristics of plant area;(4)characteristics of the stress field, including the regional stress distribution characteristics and laws, engineering area stress spatial distribution characteristics, and analog valley formation and evolution; (5) using the finite element and finite difference software to establish numerical calculation model, analyses of excavation caused secondary stress field distribution characteristics, and evaluation of the stability of underground caverns to provide a theoretical basis for support design.