Study On Meso Failure Mechanism Of Granite Based On Strain Enhancement Effect

Due to the complex stress history in the process of diagenesis,the meso mechanical parameters and macro mechanical behavior of deep dry hot rock mass are different from those of conventional engineering rock mass.As a typical representative of dry hot rock and heterogeneous rock mass,the mechanical response characteristics of granite are significantly affected by the heterogeneity of rock meso parameters,and the effect of stress history will produce strain strengthening effect,change the local rock meso parameters of granite,and affect the macro mechanical properties of granite.At present,the research on the meso failure mechanism of granite mainly focuses on the influence of the damage of granite after stress history on the meso failure mechanism,while the research on the influence of strain strengthening effect on the meso failure mechanism of granite block is less.In order to obtain the meso failure mechanism of granite test block under strain strengthening effect,this paper uses the methods of investigation statistics,laboratory test and numerical simulation to refine the meso parameter characteristics of Baima granite test block,and constructs the GBM numerical model of Baima granite.Based on the meso interpretation of strain strengthening effect,the GBM model is redeveloped,and the GBM model of Baima granite is constructed Based on the strengthening model,uniaxial compression numerical tests of GBM strengthening numerical model with different strengthening coefficients are carried out to analyze the influence of the area where the particle self-locking effect occurs in the granite block on the macro mechanical parameters of granite,and to explore the influence mechanism of strain strengthening effect on the micro fracture mechanism of granite block.The main research contents and conclusions are as follows(1)Through the XRD diffraction analysis of granite blocks and the investigation of relevant literature at home and abroad,the mineral ratio of granite blocks and the quantitative analysis results of related micromechanics are determined respectively.It is considered that the following rules should be followed in the numerical modeling of granite blocks:1)the average grain size of feldspar is larger than that of quartz and that of biotite Relationship.? The elastic modulus and tensile strength of minerals should follow the rule that feldspar is larger than quartz and biotite.Based on the above laws,the compilation process of GBM model is completed by using PFC embedded fish language.(2)The uniaxial compression and graded cyclic loading and unloading tests of granite blocks were carried out,and the numerical model was calibrated based on the uniaxial compression test results,and the GBM model of macro and micro mechanical properties of Baima granite was obtained,which matched with the actual situation.Based on the graded cyclic loading and unloading tests,the meso mechanism of strain strengthening effect was analyzed according to the residual deformation curve of the block,and it was considered that the strain inside the block followed the cyclic loading and unloading process The self-locking effect of particles caused by loading and unloading is the main reason for the strain strengthening effect.In order to characterize the self-locking effect of particles in the test block,a GBM strengthening model based on strain strengthening effect is proposed.Through a large number of laboratory tests and numerical simulation,the relevant parameters of the model are discussed.(3)Based on the established GBM strengthening model,the relevant numerical simulation work was carried out,and the meso failure mechanism of the strain strengthened block was obtained,as well as the following research results:? the peak strength of the block presents obvious segmentation effect with the increase of the self-locking effect area inside the block.?In the pre peak stage,the tensile crack propagation of the pretreated block is dominant,and the opposite is true for the undisturbed block.? The occurrence of self-locking effect not only leads to the increase of friction coefficient,but also leads to the occurrence of stress redistribution in the test block,and finally changes the failure path of the test block.? After cyclic loading and unloading,the angle peak of microcrack distribution is more uniform.