Study On The Controlling Effect Of Rock Mass Structure To The Stability Of Surrounding Rock In Underground Cavities Of Dagangshan Hydroelectric Power Station

Dagangshan hydroelectric power station is one of the main large-scale hydroelectric projects build on Dadu River. The acreage of controlling watershed around dam site reaches to 6.27×10~4 km~2,which is 81% of the whole watershed. The average flux for many years is 1000mVs and the normal water level is 1130m as planned. Backwater of the dam is 180m~190m high while the highest part of the dam is 210m. The total storage capacity is 0.742 billion m~3 with 2400MW installed capacity.Dome dam has been recommended which the left-bank underground powerhouse is located between belt I ～III composing main powerhouse, main changing house and tailwater surge chamber. As planned before the three main underground cavities have been disposed parallelly and the axes direction is N55°E. The buried depth of perpendicularity is 390m—520m which is 310m—530m for plane direction. Main powerhouse is 227.8m long, 31.2m wide and 53.4m high with soleplate 934.2m high above sea level. Main changing house is 170m long, 18.8m wide, 26m high with the altitude of soleplate is 957.8m; Tailwater surge chamber is 130m long, 20m wide, 64m high with the altitude of soleplate is 924m.The surrounding rock in the underground cavities is hoar and reddish middle granule mica adamellite with 8 dolerite veins. Taking Dagangshan hydroelectric power station as an example, this paper has studied the engineering geological characteristic of rock structure in the dam area and classified the type of it according to a lot of field work with measuring data and indoor statistical analysis.The surrounding rock of underground cavities have been graded and leveled adopting the GB50218-94, GB50267-99, RMR and Q system. Synthetical classification has been figured ou based on quantitative analysis and contrast synthesis. Also mechanics parameters for different rock types have been brought forward according to the synthetical analysis of field experiments data together with rock mass quality classification indexes.Based on the generalization model of rock structure, the 2-D finite element numerical method has been adopted to study the changing characteristic of secondary...