Study On Deformation Mechanism Of Abutment Rock Mass Of An Arch Dam In The Initial Stage Of Reservoir Impoundment

At present,when calculating the stress and deformation of abutment rock mass of high arch dam by numerical simulation,scholars mostly adopt ideal elastic-plastic constitutive models,however,the ideal elastic-plastic model can not reflect the post-peak strain softening characteristics of rocks,the results of stress,displacement and plastic zone are often inaccurate,So the deformation mechanism of abutment rock mass of high arch dam is not accurate enough.In order to solve the above problems,basalt blocks at abutment of an arch dam are selected as research objects in this paper,the strength and deformation parameters of basalt under reservoir water osmotic pressure were tested;based on the strength,deformation parameter evolution and stress-strain relationship of basalt blocks measured by experiments,with FLAC~3DD platform,using fish language to secondary development for constitutive model,a strain softening constitutive model of basalt is established,which not only reflects the deterioration characteristics of strength and deformation parameters of basalt,but also reflects the post-peak strain softening characteristics of basalt;The three-dimensional grid model of hydropower station is established,using post-peak strain softening model of basalt and ideal elastic-plastic constitutive model to predict the stress,deformation and plastic zone distribution of abutment rock mass;Based on the above research achievement,discussion on deformation mechanism of abutment rock mass under initial impoundment load.The results of the study are as following.(1)Under osmotic pressure effect,the deterioration of strength and deformation parameters of basalt is obvious.Compared with the initial drying sample,the peak compressive strength(0 MPa,3 MPa,6 MPa and 9 MPa)of the specimens after osmotic pressure of 2 MPa deteriorated by 35.48%,32.52%,26.10%and 29.05%respectively,the cohesion and friction angle deteriorated by 27.68%and 5.58%respectively,the elasticity modulus(0 MPa,3 MPa,6 MPa and 9 MPa)deteriorated by 30.91%,30.8%,28.51%and 26.71%respectively.(2)Under different osmotic pressures,the residual strength and deformation parameters of basalt sillar decrease compared with the elastic stage.The range of residual strength under confining pressure of 3 MPa,6 MPa and 9 MPa are 45.98MPa~54.28 MPa,63.08 MPa~76.55 MPa and 80.92 MPa~95.87 MPa,respectively.The range of residual elasticity modulus under confining pressure of 3 MPa,6 MPa and 9 MPa is 1.92 GPa~2.64 GPa,3.19 GPa~3.73 GPa and 3.18 GPa~4.41 GPa,respectively.The range of residual cohesion and internal friction are 3.16 MPa~7.37MPa,42.93°~54.39°,respectively.(3)According to the strength and deformation parameters with the increase of osmotic pressure evolution and stress-strain curve of basalt,the constitutive model of post-peak strain softening was established,comparing the stress-strain curves between numerical calculation and triaxial compression test,the results show that,the model can well reflect the post-peak strain softening characteristics of basalt.(4)Compared with the ideal elastic-plastic model,the maximum principal stress and minimum principal stress of abutment rock mass are slightly reduced,the range of plastic zones are increased,and the displacement is significantly increased by using the post-peak strain softening model of basalt.When the post-peak strain softening model of basaltic rock is used to predict the deformation of abutment rock mass,the results obtained are more accurate.(5)Under the initial impoundment load,the undamaged abutment rock mass has a high bearing capacity,as the water level rises gradually,the increase of arch dam thrust will inevitably lead to the increase of rock mass deformation.The strength and deformation parameters of rock mass decrease after yielding failure,lead to the bearing capacity of rock mass decreases,comparing with rock mass without yielding failure,the deformation caused by the same load is larger.