| Southwest China is rich in water and energy.Most of the large hydropower projects built or under construction in this area adopt deep-buried underground water diversion power generation system,and most of its underground powerhouses have the characteristics of "high side wall,long span".The in-situ stress field is complex and the lithology varies greatly.In the deep-buried mountain body with the development of geological structure,the stability of surrounding rock is the focus of attention during the construction period.In this paper,the initial in-situ stress in the area where the Underground Powerhouse Caverns are located is inverted and compared with the measured data.The three-dimensional seepage field is calculated and used as the basis for the stability analysis of the surrounding rock of the subsequent caverns.The excavation,anchorage support and layout of the Underground Powerhouse Caverns are calculated and analyzed in an all-round way.The surrounding rock stability of the Underground Powerhouse Caverns is recognized and evaluated correctly,and the underground caverns are verified.The rationality of excavation steps in group construction has produced theoretical support.The important research contents and results of this paper are as fol ows:(1)Inversion and fitting of three-dimensional initial geostress field of underground powerhouse.According to the topographic,geological and geomorphological conditions of the mountain body,the initial geostress field in the engineering area is obtained by the method of excavation by stages and the finite element inversion approaching the geostress value of the measured point.(2)Three-dimensional seepage field of underground powerhouse and analysis of seepage control measures.According to the measured groundwater level,the seepage field during construction period is calculated,and the seepage control measures such as drainage hole curtain and drainage gallery are simulated.It is found that the groundwater level is reduced by about 50 meters before and after the drainage hole curtain,which makes most areas of underground powerhouse above the groundwater level;the groundwater head of the factory area is greatly reduced compared with the adjacent area,and the seepage field in surrounding rock of the powerhouse and other caverns is significantly improved.The results show that the anti-seepage and drainage method has obvious effect on drainage and pressure reduction.(3)Three-dimensional integral excavation of underground powerhouse by stages and analysis of stability characteristics of anchorage support.In the same period of excavation and anchorage,anchorage measures should be taken in time after the completion of each excavation.The reasonable feasibility of the excavation method and the proposed shotcrete-anchor support measures is evaluated from the perspective of the overall stability of the cavern group.(4)The influence of earthquake action on the stability of surrounding rock of underground powerhouse.After three-dimensional integral excavation and support of underground powerhouse is completed,considering seismic action,the quasi-static method is used to calculate the stability of surrounding rock of cavern group under bolt and shotcrete support conditions,and the results are compared with those without considering seismic action.After earthquake action,the total damage volume increases by 26.9%.The plastic,rebound and crack zones of the surrounding rock of the cavern are adjusted.Most of the surrounding rock of the cavern enters the plastic zone.The stress,crack depth of the bolt at the cavern junction and the maximum plastic depth of the rock around the cavern all increase.Earthquake action has a great influence on the stress deviation tensor of surrounding rock at the junction of arch,arch seat and cavern,and also has a partial influence on the overall stability of surrounding rock of underground powerhouse. |
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