Research On Crack Propagation Characteristics Of Rock Mass Discontinuities Based On Particle Flow Direct Shear Test

The shear slip along the structural plane is the main failure mode of engineering rock mass.Direct shear test is one of the main methods to calibrate the mechanical parameters of rock mass.The test process is intuitive and concise,and the test data is true and effective.However,the shortcoming is that it can only stay in the macroscopic failure state of the rock structure surface for analysis,and it is not repeatable and nonreproducible.The microscopic nature,the limitation and complexity of this kind of experiment make it impossible to observe and evaluate the shearing process in detail.With the further development of computer technology,particle flow numerical simulation software represented by PFC has been widely used in geotechnical engineering.In PFC,the complex and changeable information of the particle flow medium can be obtained more directly,including the migration and crack expansion caused by the interaction between particles in the shearing process,and it has the advantages of optimized design and energy saving.Based on this,this paper carried out a particle flow simulation direct shear experiment to study the meso-fault mechanism of rock mass structural planes.The main work and conclusions are as follows:First,select the parallel bonding model in the two-dimensional particle flow program to establish the initial sample model,and then construct several sets of structural surfaces of different samples,and convert the related data of the known cracks or structural surfaces into the PFC particle flow software with the help of Auto CAD.In order to complete the construction of the complete structural plane rock sample model.Then adjust the meso parameters of the input sample model to calibrate the complete discontinuity rock mass sample model,analyze the sensitivity of the meso parameters,and finally draw the stress-strain curve of the model to compare with the stress-strain curve of the real indoor test,The matching degree between the two is relatively high,so as to confirm that all the parameters are adjusted.The results show that the direct shear numerical model can simulate the mechanical properties of the laboratory test well,and the error is within an acceptable range,which verifies the applicability of the model.Secondly,based on the PFC,the direct shear test of the simulated sample was carried out,and the number of cracks under different normal stress and different roughness conditions was obtained.Through the analysis of the development characteristics of the number of cracks,it was found that the The constant load and the increase of the JRC value show different degrees of positive growth,and the number of internal cracks in the sample shows different sensitivities to the constant load and the JRC value.Further analysis of the development of the number of cracks along with the displacement shows that the number of micro-cracks in the shearing process always has a positive growth relationship with the shear displacement,and the growth rate of the micro-cracks increases with the increase of the normal stress and gradually relaxes.Slowly stabilize.At the same time,the types of cracks in microcracks are studied.The number of tensile cracks is significantly higher than that of shear cracks.The type of crack growth is generally manifested as tensile cracks.The growth of shear cracks is not obvious,and it is in a stable state for a long time.Finally,the particle flow software can observe the development of micro-cracks in the sample and the displacement field under particle migration from the meso-level.First,the failure mode of the sample is discussed.Mixed failure is the main reason;secondly,through further research on the sample's direct shear test,the development and propagation of microcracks of the sample under different normal loading sizes and different morphological fluctuations are obtained.At the same time,the sample is obtained in different normal directions.The particle migration vector changes under the conditions of loading size and different morphological fluctuations,and the evolution of the sample displacement field is analyzed;finally,some special moments and the final failure moments in the shearing process are selected to determine the development and propagation state of the sample's microcracks and the particle unit The distribution of the displacement field formed by the different amounts of migration is analyzed.The results show that there are regularities in the development of microcracks and the evolution of the displacement field,which can be used as a further supplement to the test results.