Research On Dynamic Properties And Constitutive Model Of Granite With Different Level Of Defects Under Stepwise Cyclic Loading

Extensive researches have been carried on the evolution model of dynamic properties parameters of rock and the dynamic constitutive model have always been hot topics in the realm of the rock dynamics.They mainly focus on the dynamic behaviors of intact rocks and rocks with intermittent joints under constant amplitude and low-frequency(0.01Hz?3Hz)dynamic loads.While few reports studied the dynamic properties of rock masses with continuous joints,the dynamic behaviors of rocks under high-frequency(>3Hz)stepwise cyclic dynamic loads,and the dynamic constitutive model of rocks under stepwise cyclic loading.By conducting dynamic triaxial test on granite samples with various level of defects,this paper explored the influence of confining pressure,dynamic load conditions(frequency,dynamic stress amplitude,and cycle times),and the level of defects on rock dynamics parameters(dynamic elasticity modulus and dynamic damping ratio)evolution law and the influence of rock dynamic constitutive model.This research completed the following specific contents and obtained corresponding conclusions:(1)Based on the dynamic stress-strain hysteresis curves of granite with different level of defects and the microscopic deformation mechanism inside the rock,this paper studied the influence of confining pressure,dynamic load frequency,dynamic stress amplitude,cycle times,and level of defects on rock hysteresis and damping effect.This part of the research lays the foundation for the analysis of the evolution model of granite dynamic parameters.The study found that the dynamic load frequency has the most significant impact on the granite hysteresis and damping effects,followed by the dynamic stress amplitude,and the confining pressure,cycle frequency and level of defect have relatively small effects.(2)In this paper,the modified formulas of dynamic elastic modulus and damping ratio are used to calculate the dynamic parameters of granite with different levels of defects based on the rock dynamic stress-strain hysteresis loop.And the granite defect level factor D is defined.This research analyzed the influence of confining pressure,loading frequency,dynamic stress amplitude,cycle number,and defect level on the evolution law of granite dynamic parameters.The expressions of the confining pressure,frequency,stress amplitude,and cyclic cycles with dynamic elastic modulus are given,as well as the expressions of the confining pressure,frequency,stress amplitude with dynamic damping ratio.(3)Based on the internal variable theory and the relationship between dynamic elastic modulus and confining pressure,dynamic load frequency,dynamic stress amplitude and defect level,an evolution model of granite dynamic elastic modulus considering complex factors is proposed,which is suitable for the pre-peak stress stage.And then,the range of model parameters is simplified.(4)In this paper,a hyperbolic model is used to describe the dynamic stress-strain curves of granite with different levels of defects under stepwise cyclic loading in the pre-peak stress stage.And then,this paper explained the physical meaning of the parameters in the hyperbolic model and explored the influence of confining pressure,dynamic load frequency,and level of defects on the dynamic constitutive model of granite.Finally,the dynamic constitutive model of granite under graded cyclic loading considering the influence of confining pressure and loading frequency are given separately in this study.