Laboratory Experimental Study And Numerical Simulation Of Rock Tensile Strength

In rock mass engineering,tensile fracture is the main cause of instability failure of rock mass,and it is also an important factor affecting the safety and stability analysis of rock mass.How to obtain the tensile strength of rocks or rock masses is an important issue for rock mechanics researchers.On one hand,in the Brazilian splitting test,due to the existence of the Poisson effect,the tensile strength obtained from the test must be closely related to the thickness of the sample,which is inconsistent with the calculation formula of the Brazilian splitting test based on the plane assumption.On the other hand,how to determine the tensile strength of jointed rock masses in the field is also a problem faced by rock mechanics.In order to study the method of obtaining tensile strength parameters of rock or rock mass,influencing factors,and the anisotropy and size effect during tension and failure of jointed rock mass,the Brazilian splitting test and direct tensile test method were used in this paper.The size effect and anisotropy of tensile strength of jointed rock masses are expected to reveal the three-dimensional effect of the Brazilian splitting test,and a numerical test method for obtaining rock mass tensile strength is proposed.The main results of this paper can be concluded as follows:(1)Three-dimensional study of the rock splitting test and direct tensile test were carried out to investigate the effect of different thickness-diameter ratios on tensile strength and splitting failure characteristics of the rock discs.The effects of tensile strength and fracture process are as follows:(1)Splitting tensile strength is significantly influenced by the disck thickness.The greater the thickness of the disk,the lower the tensile strength,and the initial crack occurs at the middle section of the outer surface.The longitudinally extending form is a linear splitting crack and gradually penetrates through the thickness direction.(2)In the direct tensile test,the three-dimensional effect has little effect on the tensile strength.Numerical simulation can clearly explain the effect of thickness on the fracture mode.(2)Taking into account the influence of Brazilian splitting test and direct tensile test on the determination of deformation parameters,based on RFPA~2DD numerical software,the size effect simulation of tensile strength of jointed rock mass was studied,and the evolution of strain field and acoustic emission field was obtained.In the process,the unit size of the characterization unit of tensile strength was determined.The study showed that:(1)The tensile strength obtained by two different strength measurement methods indicated that the unit size was the same;(2)The failure modes of Brazilian splitting test were mostly along the loading direction.Splitting fractures,but in the direct tensile test,mostly along the weak joint surface of the shear-crack complex damage.(3)Brazilian cleaved and direct tensile simulations of jointed rock masses with different angles were carried out.The effects of two test methods and joint angles on the tensile strength anisotropy were compared and analyzed.It was found that both test methods existed.With the anisotropy of tensile strength,the tensile strength decreases first and then increases with the change of the joint angle.The curve shape is elliptical.This paper focuses on the problems in the test methods for the tensile strength of rocks or rock masses,and studies the influence of disc thickness on the tensile strength and tensile fracture modes in the Brazilian splitting test,and uses random fissure network simulation to establish the jointed rock.The numerical calculation model of the volume is used to study the size effect and anisotropy of jointed rock mass by conducting large-scale Brazilian splitting test and direct tensile numerical test,and to provide theory and method for determining the tensile strength parameters of rock or rock mass.The support on the rock mechanics test methods and engineering applications have a certain theoretical significance and engineering application value.