Study On Crack Propagation Law Of Heterogeneous Fractured Rocks Based On Grain Based Model

With the development of large-scale infrastructure projects in recent years,rock related projects have gradually become the focus and mainstream of infrastructure construction,and the research on the failure mechanism of fractured rock has always been a hot issue in the field of geotechnical engineering.At present,most of the researches on the failure mechanism of fractured rock at home and abroad are based on Laboratory mechanical tests and numerical simulation software,and a lot of results have been achieved.However,most of the researches on fractured rocks are from the macro perspective,and the heterogeneity of minerals in rocks is seldom considered.However,the study of fractured rock from a single macro perspective can not meet the needs of basic science and engineering practice in China.This paper attempts to reveal the failure mechanism of fractured rock from the meso level of rock mineral heterogeneity by means of PFC numerical simulation software and related laboratory mechanical tests.The composition and structure of rock minerals are the root of the heterogeneity of rock materials.In order to study the influence of microstructure heterogeneity on macro mechanics and crack propagation law of fractured rock,based on the obtained macro and micro mechanical parameters of a quarry in Baochuan City,South Korea and Pingyi County,Shandong Province,mineral models for these two different types of granite are established by using PFC discrete element numerical software The grain based model(GBM),combined with the results of uniaxial compression test and numerical simulation of rock with single crack,verifies the rationality and reliability of GBM.Uniaxial and biaxial compression numerical tests are carried out on double fractured rock samples to analyze the influence of meso anisotropy on the failure mechanism of fractured rock.The main findings of the research are:(1)With the help of PFC numerical simulation software,GBM models for two kinds of granite in a quarry in Baochuan City,South Korea and Pingyi County,Shandong Province were established.The parameters of the models were calibrated by "trial and error" method,and the influence of meso parameters of the models on macro mechanical properties was studied by parameter variable method.The results show that the uniaxial compressive strength of rock increases first and then decreases with the increase of stiffness ratio The results show that the peak strength reaches the maximum when the stiffness ratio is between 1.0 and 1.5;the elastic modulus of rock samples increases with the increase of stiffness ratio and tends to be stable gradually;the friction coefficient and friction angle have little influence on the elastic modulus of the model,mainly affecting the compressive strength of the model;the cohesion and the tensile strength of the bond affect the tensile strength and the tensile strength of the model respectively The relationship between the two groups of data is approximately linear.(2)Uniaxial compression tests were carried out on granite samples with single fracture angles of 15,30,45 and 90 degrees in Pingyi County,Shandong Province.The results show that GBM model can effectively simulate the strength and failure mode of fractured rock on the basis of considering the heterogeneity of crystal structure and strength of rock and mineral,and can study the crack initiation,propagation and evolution law from the micro perspective,which is an effective method to study the heterogeneity of rock;the mechanical properties of prefabricated single fracture rock samples with different dip angles during uniaxial compression It can be divided into three stages: elastic stage,crack propagation stage and failure stage.There are two main forms of specimen failure: tensile failure and shear failure.The crack types are mainly divided into wing crack and anti wing crack.There is a certain correlation between anti wing crack and shear failure.(3)Uniaxial and biaxial compression tests were carried out on rock samples with double fractures distributed in different fracture positions.The results show that the crack morphology of the two GBM models is in good agreement with that of the indoor test;During the loading process of double fractured rock,the crack development mainly goes through the initial stage,stable development stage,rapid development stage and post peak stage;Compared with uniaxial compression test,biaxial compression test of rock with double cracks under 10 MPa confining pressure has the characteristics of central symmetry and edge ductility;From the point of view of strain crack number,the confining pressure has different degrees of inhibition on the development of other types of cracks except intergranular shear cracks.The heterogeneity coefficient is used to quantitatively describe the heterogeneity of two kinds of rocks,and the influence of heterogeneity on the failure mechanism of double fractured rock is studied.The results show that the rock with large heterogeneity coefficient is more prone to stress concentration during loading,and the failure mode is easier to transform from tensile failure to shear failure under biaxial compression.(4)The results show that the double fractured rock with large heterogeneity coefficient is more prone to stress concentration during loading,and the failure mode is easier to transform from tensile failure to shear failure under biaxial compression.