Study On Rheological Properties Of Rock Under Periodic Large Fluctuation Of Reservoir Water Level

According to the Rock rheology of the bank slope and rock under the large fluctuation of reservoir water level,taking the slope red sandstone in the bank of Chongqing area as the research object,considering the large fluctuation of reservoir water level in reservoir area,the method of laboratory test,theory analysis and numerical simulation is adopted.In this paper,the instantaneous mechanics of red sandstone and the creep characteristics under large fluctuation of reservoir water level are studied,and the nonlinear visco-elastic-plastic creep model considering the variable reservoir water pressure is established based on the test results.Using particle flow discrete element software PFC3 D,to carry out the corresponding numerical simulation work,the main research contents and results are as follows:(1)Through the conventional compression test,the characteristics of the deformation and strength of the red sandstone under different water state(natural and saturated)and different confining pressure are analyzed,and the cohesive force and the internal friction angle of the specimen are obtained.The influence of different water content on the peak strength and elastic modulus of the specimen was studied,and the relationship between the fracture angle and confining pressure was revealed.(2)The Creep tests of different water state(natural and saturated),different confining pressure and variable water pressure were carried out,and the effects of different confining pressure,different stress levels and different water state on creep deformation and creep rate of red sandstone were studied based on the test results.Comparing with saturated specimens,the changes of the instantaneous strain,creep and creep rate of red sandstone under variable reservoir water pressure are analyzed,and the influence of water pressure on the creep is discussed.(3)By studying the characteristics of creep viscoelastic stage under different conditions,the nonlinear expression equation of deformation modulus with variable reservoir water pressure and time is found,the equation is introduced into Kelvin model,and an improved nonlinear generalized Kelvin model is obtained.The acceleration creep stage is fitted by exponential function,the nonlinear creep equation and the nonlinear viscous element satisfying the viscous coefficient changes with the variable reservoir water pressure and time are obtained,and the element is introduced into the Bingham model to obtain a nonlinear Bingham Visco-plasticity model.A nonlinear visco-elastic-plastic creep model of red sandstone under variable reservoir water pressure is established by series of nonlinear generalized Kelvin model and nonlinear Bingham model.The three-dimensional constitutive equation and creep equation are deduced,and Origin is used for nonlinear fitting.(4)Based on three-dimensional particle flow theory,the meso-structure model of red sandstone is established by using the particle flow discrete element software PFC3 D,the meso-mechanics parameters of the conventional and creep tests of red sandstone are determined according to the laboratory test results and the PFC3 D parameters identification method,and the meso-mechanics numerical model of red sandstone is constructed.(5)Based on the meso-mechanics numerical model of red sandstone,the numerical simulation of instantaneous mechanics and creep mechanics is carried out.In this paper,the deformation characteristics,cohesion,internal friction angle and crack initiation strength of the red sandstone are analyzed,and the evolution process of the deformation and fracture at the microcosmic layer and the law of the crack distribution in different states are studied.According to the creep-time curve of laboratory test,the evolution law of the microscopic deformation and fracture of red sandstone at each time node is given,the accelerated creep characteristics of red sandstone under different variable reservoir water pressure and the change rule of destruction time are obtained,and the results show that the accelerated creep failure time of red sandstone under different variable reservoir water pressure is exponential downward trend.