Study On Failure Evolution Characteristics Of Jointed Rock Mass Based On Direct Shear Test

Rock mass is a kind of geological body widely distributed in the field of geotechnical engineering.During the long geological period,rock mass is affected by many kinds of actions in the process of formation.Therefore,there are a lot of structural planes in the rock mass: joints,bedding,faults and so on.The interaction between these structural planes results in a complex structure,which makes the rock mass very complex.Because of the complexity of the rock mass structure characteristics of the joints and rock bridge deformation in rock failure process in damage evolution and expansion,strength contribution problem is still not solved well,has been a hot and difficult problem in rock mechanics field of attention.This paper mainly aims at the joint rock failure process,joints and rock bridge deformation and failure and problems of the development of engineering mechanics characteristic and deformation strength,evolution,development of indoor direct shear test,to provide technical support for engineering mechanical parameters of jointed rock mass.The research contents of this paper are as follows: three aspects:(1)Design of structural surface distribution pattern and design of test scheme in laboratory model test:In the structure of the distribution pattern based on analysis of probability statistics,combined with the existing structure of the rock mechanics strength theory and literature in the distribution pattern,design 13 including 3 structure through joint distribution pattern,and the complete set of rock and rock mass containing discontinuous joints completely as control group.According to direct shear test to obtain the strength of jointed rock mass mechanical characteristics,to make full use of the available test equipment and other conditions,feasible and reasonable design of jointed rock mass shear test scheme,and the design of the sampling system in direct shear test data and images.(2)The typical distribution pattern of rock mass structural plane a total of 47 trials,the comparative analysis of the image data and monitoring data of 47 tests,study under different normal stress conditions,the same kind of jointed rock joint expansion,failure process,type of stress-strain curves and ultimate failure path type.The results show that the failure process of jointed rock mass stress-strain curves can be divided into six stages: compaction,elastic deformation,crack,crack,contact crack growth and residual deformation stage;six types: cut type,brittle type,sliding type,yield type,composite type,cut the brittle fracture of composite type.(3)The data of 47 direct shear tests of jointed rock masses are analyzed and sorted.The weighted average strength criterion(Jennings method)and the modified strength criterion based on Lajtai method are used to verify the results of direct shear tests of jointed rock masses.The results show that: in the normal stress for 1.5MPa and 2MPa conditions,the shear strength parameters are obtained by the tests of high shear strength of jointed rock mass calculated by Jennings(the absolute value between 1.8%~27.5%);Lajtai rock bridge failure theory to calculate the shear strength based on low(absolute value between 0.9%~26.6%),the relative error is relatively small.