A Statistical Damage Simulation Method Of The Full Nonlinear Deformation Process For Rocks

Natural rock is not fully compact material,instead,it inevitably contains a number of initial voids;on the side,if the stress on the rock continues to increase after the yield strength is reached,the rock will damage.These reasons make the deformation properties of the rock is very complicated,the stress-strain curves present non-linear characteristics,and there are difficulties in describing the relationship between stress and strain by the classic elastic mechanics directly.On that account,the core research content of this paper is the simulation method of the full nonlinear deformation process for rocks.Through the triaxial compression tests,the full nonlinear deformation process for rocks can be divided into five phases:nonlinear initial deformation phase、linear elastic phase,strain hardening phase,strain softening phase and residual strength phase,in addition,at the linear elastic deformation phase,the elastic modulus of some rocks will vary with the confining pressures.To establish a simulation method of the full nonlinear deformation process for rocks,firstly,this paper analyzes the mechanical properties of different types of voids and discusses the deformation mechanism as well as characteristics of the full nonlinear deformation process,based on this,a rock will be abstracted into two parts such as rock matrix and flaw material,furthermore,the method to describe the deformation relationship between macroscopic rock and its components has also been set up,whereupon,the model to analyze the rock macroscopic deformation will be obtained by means of researching the deformation of flaws material and rock matrix respectively.On the part of the flaws material,its compression deformations are unrecoverable and need continuous increasing stress,the deformation model can be obtained by instantaneous strain analysis method.As for the the rock matrix,considering the possible variation of elastic modulus with confining pressures for some rocks,it is prior to bulid the rock matrix elastic modulus variation analysis method before the deformation analysis model is set up.In view of the fact that rock matrix bulk compliance mainly depends on the number of unclosed cracks inside,hence,through the establishment of the relationship between the number of unclosed cracks inside the rock matrix and the crack aspect ratios,and the introduction of the relationship between crack aspect ratios and the pressures on the rock matrix as well as between the bulk compliance and the elastic modulus,the analysis method of the variation of elastic modulus with confining pressures will be gained.On this basis,by adopting the statistical damage theory while taking the effects of damage threshold and residual strength into consideration,an analysis method for the rock matrix deformations has been developed.Afterwards,a new statistical damage constitutive model which can simulate the full nonlinear deformation process of rocks has been set up while a determination method for the model parameters by the triaxial compression experimental curves of rocks has been also provided.This model possesses the superiorities of existing similar models,it can describe the characteristics of strain hardening and strain softening during the full deformation process,at the same time,it can also present the characteristics of the nonlinear initial deformation at low stress level and the elastic modulus variation at the linear deformation phase as well as the deformation characteristics on the post-peak residual strength deformation phase.Finally,its rationality and superiority have been also demonstrated by the comparison analysis among the experimental and theoretical curves of the proposed and other similar models.