| Yagen hydropower station is located in the main stream of the Yalong river, Which is the second cascade hydropower stations in the middle reaches. The explorations of Pre-feasibility stage showed that there are Ripping loose rock mass between I and V exploration lines in the front of the dam, it is about 850m along the river and is 808 million cubic meters. There is apparent deformation and failure along the crannies. Surveying its border, distribution and deformation and fracture characteristics, and analyzing its genetic mechanism and the deformation and failure mode, is significant to forecast its stability of every condition in water storage and evaluate the influence to Yagen hydropower station. The paper is meaningful to study the deformation and failure mode of deep canyon in high stress field.The paper worked on the rock structure and deformation and fracture characteristics, also the geo-environmental conditions of ripping loose rock mass thoroughly, to find out its deformation and failure mode of geomechanics. Combined with the regional geological conditions, evolution history of valley landforms and deformation and fracture characteristics of granite in unloading state, the paper analyzed the genetic mechanism and constituted the formation and evolution mechanisms of ripping loose rock mass. The paper used Numerical simulation of finite element to reproduce the process of ripping loose rock mass. Then, the paper evaluated the control effect of rock mass structure of ripping loose rock mass. Details and results are as follows:(1) Based on regional tectonic setting, regional landforms and new formation activity, the paper analyzed the region background conditions giving birth to high stress. Combined of regional stress field and earthquake focal mechanism, the paper founded that the study is in the stress field (NWW～EW) now. Information of surveying stress of dam site showed that Contour of SMin is Vertical towards valley(NEE), the value is 17.7Mpa in the vertical depth of 122m. So, the study area is of high tectonic stress.(2) The paper did systematical research to granite rock structure of study area, and studied the faults and crannies in detail, to find the space diversity and make the structure of district. 1# ripping loose rock mass slope is characterized by faults(N40-60°W/SW∠60-75°), and the slope is plate structure dumping within steep slope. Based on the development features of low-angle structure, 1# ripping loose rock mass slope was divided into two subregions, because YI-1 subregion growed low-angle faults and YI-2 subregion growed low-angle crannies.(3) Based on the deformation and failure characteristics, ripping loose characteristics and test results of Seismic CT, combined of rock mass structure of slope, the paper determined the distribution and boundary of ripping loose rock mass, and analyzed its nature of engineering geology.(4) Based on the deformation and fracture characteristics, combined of rock mass structure and evolution history of Valley landforms, the paper put forwarded 7 kinds of deformation and failure modes: :①thrust-shear dilatation along low-angle structures ;②toppling deformation;③Different rebound along low-angle structures;④Board cracking of the intact rock;⑤Relief cracking along middle-steep-structure;⑥Slippage-cut-crack;⑦Squirm-slipping and slipping-pressed-crack;(5) Through study of granite's mechanical properties, rock mass structure of slope, high stress field and characteristics of valley landforms, from the angle of control of rock mass structure and evolution of valley landforms, the paper analyzed the causes of ripping loose rock mass. 1# ripping loose rock mass is special granite rock mass under high geo-stress, and its was formed by transformation of deformation and fracture, accompanying relief process, release and adjustment of high stress. Then, the paper established two model of typical causes of ripping loose rock mass.(6) The paper selected low-angle faults (f01-6,f01-1-7 and f03-17), steep-inner faults (F2,F3,F5) and lateral control fault (F8), to establish ancestor slope structure. Imposing structure stress, the paper used Numerical simulation (FLAC3D) of finite element to reproduce the formation of ripping loose rock mass by 5 steps.(7) Based on the stability controlled by rock mass structure and engineering excavation measures, the paper evaluated structure effect of ripping loose rock mass comprehensively. |
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