Research Of Mechanical Property And Evolution Of Mesoscopic Mechanism Of Brittle Rock

Brittle rock of deep excavation with phenomena such as rock burst have greatrelationship with the evolution of deformation and destruction mechanism of brittlerocks under high ground stress and complex stress condition, with the increase ofstress level and complication of stress path, the law of deformation and failure ofbrittle rock strength differ significantly with shallow condition under low stresscondition, the traditional constitutive model can’t well describe the deformation andfailure and strength characteristics. For years research of the of evolution deformationand damage mechanism of brittle rock under the condition of high in-situ stress isvery limited. as the basis theory of stability and control measures of brittle rockexcavation, how to understand brittle rock mechanics characteristic has become aproblem to be solved. According to the above, this paper will apply true triaxial test tostudy the mechanics characteristic of brittle rock, by using PFC^3Dparticles blocktheory to establish a detailed numerical model of rock. This paper will put forward thebrittle rock true triaxial loading/unloading method and control process andmesoscopic parameters determination method. By test using numerical model thepaper obtained the different stress path deformation failure mechanism of brittle rockunder different stress level and applicability of strength criterion to brittle rock. Thetrue triaxial test and numerical test are compared in detail, deeply recognize theevolution of deformation and destruction mechanism and strength characteristics ofbrittle rocks.The main work and research results of this paper are as follows:1. The introduction systemly summarizes the current research status, the currentresearch status, the research methods and main conclusions of brittle rock, analyzesthe main problems existing among them. According to that, this paper puts forwardthe main research contents and research methods, determine the main technical routeof brittle rock testing and implementation plan.2. In the second chapter the author carried on the marble true triaxial test, got thedeformation, strength and destruction, energy, acoustic emission, ultrasonic changerule, and depthly analysed the evolution of deformation and destruction mechanismand strength characteristics of brittle rocks under four kinds stress path.3. In the third chapter the author analyzed the PFC3D particles block modelingmethod, commonly used model parameters and research steps. By conducting the sensitivity analysis of particle mesoscopic parameters, the author studied thecorresponding relationship between macroscopic and mesoscopic parameters of rocks,the results show that the rock elastic modulus, poisson’s ratio, peak strength had greatrelationship with particle system stiffness, friction parameters, bond strength, bondstiffness, particle shape, proportion of particle blocks for a linear or logarithmicrelationship model.4. By PFC^3Dnumerical test, the four kinds of stress path including stress level oflow and middle and high under a single sample detailed simulation and comparison,the results showed that the condition of low stress poor fitted, condition of high stresseffect fitted well. As for the damage mechanism, test group2with unloading failuremode, its true triaxial test with confining pressure increasing show the change rule oftensile and shear–shear and tensile–shear failure, while the result of numericalexperiments has the change rule of tensile-tensile-shear failure.5. By using the average parameter inverting from true triaxial test,five groupsfor the mesoscopic parameters of the numerical experiment are conducted. Thedeformation of two direction of confining pressure are analyzed in detail, especiallythe numerical testing group3and4, for each minimum principal stress, there is acritical intermediate principal stress that the deformation of the sample of postdestruction change from expansion to squeeze. Four groups of broken and shearfailure number along with the change of stress level of stress path are analyzed, wefound that when the tensile rupture dominated the rupture number,the sample damageperformance is tensile failure mode, when the tensile rupture and shear rupture areabout of equal, the sample damage performance is tensile-shear or shear-tensilefailure mode, when the shear rupture dominated the rupture number, the sampledamage performance is shear failure mode. The fifth group of numerical testemphasized on the applicability of the strength criterion of brittle rock. We found thatconsidering the intermediate principal stress changes in the modefied Wiebols-Cookstrength criterion is best fitted to describe the strength of the rock material used in thenumerical test.6. Circular tunnel excavation under different stress levels are simulated by PFC^2D,studying the destruction rule of it. The results show that the damage is given priorityto with tensile failure, the higher stress level, the damage broader, the more prone tobe variant rock burst phenomenon, but the scope is relatively small.45°jset structurein the face of circular tunnel excavation was simulated, the influence of the results showed that the dig face by far into structural plane leave, rock burst type should bevariant by rock burst into the destruction of the structure plane as the damageboundary type, and a relatively large range.