Study On Shear Mechanical Behaviours Of Multi-joint Structures Of Rock Under Constant Normal Stiffness Conditions

The stability of a rock mass concerns the safety and benefits of both construction and operation of all rock projects,such as the mining,transportation,water conservancy and hydropower engineering,national defense engineering and so on.Considering the stability of rock engineering based on the structure of engineering rock mass involves the basic concepts and treatment methods of understanding the stability of rock engineering.The rock mass dislocates and slips along the joint plane,resulting in the deformation and failure of geotechnical engineering.What's more,in deep underground engineerings?i.e.mine roadway and deep underground rock tunnel?,the CNS boundary conditions is more applicable,because the normal stress that is applied perpendicular to the direction of shear is not a constant.There is no complete and effective understanding about the mechanical behavior of rock joints,up to now.Therefore,it is of great significance to study the shear mechanism of rock joints under a CNS condition.The research was funded by the National Natural Science Foundation Key Projects of China?Basic theory of informatization control for deep mining and structural stability of roadway surrounding rock mass,Grant No.51734009?and the National Key Basic Research and Development Program of China,?No.2017YFC0603001?.This research studied the shear behaviors of rock joints in underground engineering with the help of CNS Shearing Instrument of Nagasaki University,Japan.A systematic study was carried out by combining physical model tests?Maximum shear displacement is 2 cm?,particle flow numerical model tests and theoretical analysis.In the physical model tests,243 specimens were poured with artificial similar materials.The main results are as follows:?1?The influence of JRC on shear behavior of rock joints is quantitatively analyzed by physical model tests,and the effects of boundary conditions and the normal stiffness on shear behavior of rock joints are discussed.The JRC plays an important role in the shear behavior of rock joints,and the shear strength of a specimen increases with the increase of JRC.There are obvious differences in the shear behavior of a rock joint under CNL and CNS conditions,and these differences are mainly reflected in the post-peak stage.The shear behavior of a rock joint is sensitive to the change of normal stiffness.The increase of normal stiffness can increase the shear stress and normal stress,which can further limit the joint dilatancy.?2?The anisotropy of rock joints under CNL and CNS boundary conditions is further studied for the single-joint specimens,and the inclination angle of the critical waviness of surface profiles is used to describe the anisotropic of the joint surface.The inclination angle of the critical waviness of surface profiles is well correlated with the evolution of the normal displacement and the mass loss of the specimen.However,the shear stress,normal stress and the normal displacement are often overestimated when using the inclination angle of the critical waviness of surface profiles to evaluate the joint surface roughness.It is necessary to revise the estimated value in the future work.?3?The shear tests of unfilled and infilled rough rock joints under cyclic loading and CNS conditions were conducted.The influences of initial normal stress,normal stiffness and shear velocity on the shear behaviors were estimated and analyzed.Six mathematical models for predicting ?,?_n and ?_v of unfilled and infilled rock joints under cyclic loading and CNS conditions are proposed.?4?On the basis of the above research,the evolutions of shear stress,normal stress and normal displacement of the specimens are systematically analyzed,and the failure mode of joint surface is quantitatively described by binary method.In the shear test of multi-joint rock specimens,the effects of JRC,joint number and joint spacing on the shear behavior of specimens are investigated.Based on the test results,a regression function for predicting the Surface Resistance Index?SRI?of multi-joint rock specimens is proposed.?5?Based on the physical model test,the shear behavior of the rock joint network is systematically studied by using PFC^2D software.Through the self-compiled PFC^2D program,the process of constant normal stiffness boundary condition,rough joint introduction and joint cyclic assignment in shear process are realized,and good results are obtained in numerical simulation experiments.Based on the above research,the effects JRC,initial normal stress,normal stiffness,shear rate and random multiple joints on shear stress,normal stress,normal displacement and failure mode of specimens are quantitatively analyzed.The random joints in rock mainly affect the failure mode of the specimens,while the main joint in rock controls the shear properties of the specimens.This paper has 118 figures,10 tables and 154 references.