Study On Effect Of Cavern Excavation On High-steep Rock Slope With Water Inlet

The inlet slope is very important for the safety of the inlet building and the normal operation of the underground workshop.Especially,the inlet slope of the lower reservoir of the pumped storage power station has steep terrain and complex stress distribution.Moreover,the excavation of the engineering slope and cavern has a great disturbance to the slope,and the stress will be adjusted many times,which has a great influence on the safety and stability of the whole slope.In this paper,based on the project of Longyangxia Large-scale Energy Storage Plant(LLESP),the water inlet slope of the following reservoir is taken as the research object,and a variety of field data collection methods,field mechanical tests and numerical tests are adopted to carry out researches on the characteristics of natural rock mass in the slope area,slope grading excavation effect of slope rock mass and subsequent excavation effect of water conveyance tunnel of slope rock mass.The main achievements of the research are as follows:(1)The characteristics of rock mass in the high-steep slope of the lower storage inlet of the LLESP are studied detailly due to a variety of survey results and field tests.Based on three-dimensional laser scanning,unmanned aerial vehicle(UAV)tilt photography,surface survey,structure planes cataloging and fine measurement in the adit,the characteristics of structure planes were studied,and the rock mass structure of the inlet slope were analyzed.On this basis,the quality of rock mass is evaluated according to the field test.The characteristics of slope structure and deformation and failure mode of slope are analyzed in combination with free face.The rock mass structure in the inlet slope area is mainly sub-massive structure,Mosaic structure and massive structure are less developed,and only a few areas appear cataclastic texture.The surface rock mass quality of the slope is mainly grade Ⅲ rock mass,and locally grade Ⅳ rock mass is developed.In the shallow surface of the inlet slope,the slope structure controlled by sliding surface is mainly developed,and the slope structure controlled by steep dip joints is developed in the steep slope area.The exposed bedrock is mostly monolithic and massive,and a little bit appears as a cataclysmic slope.Based on this,combined with the signs of deformation and failure,the deformation and failure modes and mechanisms of four categories and ten subcategories in the slope area are studied.(2)Based on the spatial distribution and temporary evolution characteristics of stress field and displacement field of high-steep inlet slope,the responses of multi-level slope under stage-by-stage excavation are explained.Combining with the preliminary design and excavation process of slope,the geological and mechanical model of slope was generalized according to the characteristics of rock mass and slope structure in the study area,and the response characteristics of slope rock mass under stage-by-stage excavation condition was explained on the basis of continuum theory.The multi-level slope excavation results in obvious stress redistribution.The stress increases in the horizontal direction of the slope,and then decreases with the depth increasing,and tends to the characteristics of initial stress.The response of the minimum principal stress is more obvious than the maximum principal.The displacement response of shallow surface rock mass is roughly the same.The displacement of rock mass in the central slope is larger than that of rock mass at the top and foot of slope.And it becomes more obvious as the stage-by-stage excavation.(3)Based on the evolution laws of stress field and displacement field of rock mass in the slope under the excavation of tunnel,the effect of subsequent excavation of highsteep slope on water inlet is revealed.It shows that the influence of cavern excavation on the slope is mainly concentrated on the rock mass near the cavern.The stress concentration of the rock mass is obvious within the range of three times the diameter of the cave,and the stress tends to the initial stress with getting further away from the cavern.In the axial direction of the cavern,the stress of rock mass on both sides increases with the increase of the carven depth.The displacement of rock mass around the carven reaches its maximum at the wall,and decreases rapidly within the range of two times the diameter of the carven.Cavern excavation has little effect on rock mass beyond three times its own diameter.