Determination Of Shear Strength Parameters Of Mudshale In Gushan Reservoir

With the rapid development of water resources and hydropower in China,shale stratum is one of the strata with poor geological conditions which are often crossed during the construction of reservoir area.Due to the characteristics of muddy shale softening in water,large deformation and collapse often occur during dam construction,which heavily threatens the life and property security of the people around the reservoir area.Selecting mechanical parameters of weak rock mass has always been a key problem in reservoir design and construction.Therefore,it is necessary to study the shear strength parameters of shale in combination with engineering practice.Based on the Gushan Reservoir in Xin’an County of Luoyang City under construction,large direct shear tests are carried out indoors and outdoors,and numerical simulation of indoor tests is carried out by PFC2D.The cohesion c and internal friction angle J of shale shear strength parameters in Gushan Reservoir are studied.The following conclusions are drawn:(1)According to the large direct shear test in situ,the shear strength parameters of muddy shale in Gushan Reservoir under natural and saturated conditions are as follows:in natural condition,its internal friction angle is 23.9 degrees and cohesion is 33.957 KPa;in saturated condition,its internal friction angle is 15.38 degrees and cohesion is 12.33 kPa.The results show that under saturated condition,the hydration of shale is obvious,and the mechanical properties change significantly.Compared with natural condition,the shear strength parameters decrease significantly.(2)Based on the large direct shear test in the field,the shear strength parameters of muddy shale in Gushan Reservoir under natural and saturated conditions are obtained as follows:in natural condition,the internal friction angle is 29.9 degrees,the cohesion force is c=40.04KPa;in saturated condition,the internal friction angle is 21.6 degrees,and the cohesion force is 25kPa.The parameters of shear strength obtained from laboratory tests are larger than those obtained from field direct shear tests.This is mainly due to the large disturbance in the process of taking,transporting and testing,the serious damage of natural structure of rock samples,and the filling of voids with rock debris.The test results show that,combined with field large direct shear test,indoor large direct shear test can show the mechanical properties of shale to a certain extent.Although the two test methods have their advantages and disadvantages,they can accurately reflect the relationship between stress,strain and displacement in the shear process by complementing each other,so as to improve the reliability of obtaining shear strength parameters.(3)Using PFC2D particle flow process,the numerical simulation of laboratory tests was carried out,and the shear strength parameters of muddy shale in Gushan Reservoir under natural and saturated conditions were obtained as follows:under natural water-bearing conditions,the internal friction angle was 22.7 and the cohesion was 57.2 kPa;under saturated conditions,the internal friction angle was 20.27 and the cohesion was 24.23 kPa.The simulation results of direct shear test of shale show that the mechanical properties and stress-strain relationship of shale are basically consistent with those of laboratory tests.The development of shear surface cracks and the law of force chain transmission distribution in the process of shear failure are further studied,and the meso-failure process of shale is further understood.(4)Comparing the results of indoor and outdoor large direct shear tests and simulation tests to verify the correctness of the test results,the shear strength parameters of muddy shale in Gushan Reservoir are concluded as follows:in natural water-bearing state,the range of internal friction angle is 22.7～29.9and the cohesion is 33.96 kPa～57.2 kPa;in saturated water-bearing state,the range of internal friction angle is 15.3.The cohesion is 12.33kPa～25kPa.