A Study On The Scale Effects Of Strength And Deformation Characteristics For Jointed Rock Masses

The jointed rock mass is investigated as a main object in this paper.Researches on the mechanical characteristics of random jointed rock mass are one of important topics in rock mechanics and engineering.The size effect of jointed rock mass,including its deformation and strength parameters,is studied using finite element method.According to the laws of the probability distribution of random joints in rock mass,how to generate the random joint network is to be explored.Then,the program is given using MATLAB software.A series of numerical specimen with different sizes of jointed rock mass are established by Monto-Carlo method.The characteristic size effect for the deformation and strength parameters of random jointed rock mass is systematically deliberated.The contents of this paper can be outlined as follows:1.The mechanical models of the jointed rock mass are briefly introduced.The methods of studying the size effect of deformation and strength parameters for the jointed rock mass are generally discussed.The basic principles of equivalent deformation and equivalent strength are summarized.The mechanical behavior of joint is simulated using six-node isoparametric joint element and ordinary isoparametric element.It is shown that the fact that the joint is treated as ordinary isoparametric element with some thickness is reasonable.2.The rock mass is composed of intact rock with joints.The probability distribution of random joint usually follows certain rules in rock mass.The two-dimensional randomly distributed joint network is automatically simulated using MATLAB functions.Its feasibility is also verified by several instances of random joint network generation.3.Based on two-dimensional random joint network diagram,the intact rocks and the randomly distributed joints in the selected calculation domain are automatically divided into triangular finite element meshes using dismesh2 d function,which provides the basis for numerical simulation of mechanical parameters of random jointed rock mass.4.A series of rock mass numerical specimen with randomly distributed joints are constructed using Monto-Carlo method.These numerical specimens with different sizes are divided into different groups.The deformation behaviors of these specimens are simulated by finite element method with ABAQUS software.According to the obtained stress-strain relationship under different scales,it is found that the deformation characteristics of jointed rock mass have obvious scale effect.The stress-strain curve gradually converges when the size of numerical sample becomes larger.The scale effect of the elastic modulus of jointed rock mass is studied on the basis of systematical analysis of stress-strain curves for these specimens with different scales.The REV of the elastic modulus for simulated jointed rock mass is estimated according to the fitted curves of elastic modulus vs.the specimen size.5.The strength characteristics of jointed rock mass numerical specimen is researched under different confining pressures.The uniaxial compressive strength of theses specimen and its size effect are analyzed.The scale effect of the uniaxial compressive strength is discussed according to the fitted curves of uniaxial compressive strength vs.the model size.Based on Mohr-coulomb strength criterion,the cohesion c and internal friction coefficient f are calculated under different confining pressures.The scale effect of cohesion c and internal friction coefficient f are profoundly investigated by their respective fitting curves of the cohesion c or internal friction coefficient f vs.the model size.