Experimental Research On The Shear Strength Of Thinly-infilled Rock Joints During Shearing

The rock mass is a multi-fracture body with a certain structure,which is cut vertically and horizontally by the structural plane,and there are a lot of rock joints in the structural plane,most of which are filled joints.Due to the existence of fillings,the shear strength of rock joints will be significantly affected,so it becomes the key factor to control the stability of various rock mass engineering.Among them,thinly-infilled rock joints are widely distributed,and the study of their shear strength characteristics can provide a theoretical basis for the stability analysis of slope,dam and underground cavern,which is of theoretical and practical significance.Selecting the 5th¹0th standard joint profiles proposed by Barton as the production basis of irregular rough rock joint surfaces.On the basis of fine digital processing,the accurate reconstruction of joint surface with standard roughness is realized through 3D printing technology.With quartz sand as the filling medium and cement slurry with a water-cement ratio of 0.44,a total of 90 groups of thinly-infilled specimens with five infill thickness to asperity height ratios?0.0,0.25,0.50,0.75 and 1.00?were prepared.The following studies were carried out:?1?According to the thinly-infilled rock joints specimens for normal stress level 3?0.2?_c?0.5?_c?0.7?_c?under the laboratory direct shear test,get filling joint shear stress and shear displacement curve and peak shear strength,the peak shear strength increases with the joint surface roughness increases,decreases with increasing infill thickness to asperity height ratio,along with the normal stress increases;?2?Shear failure characteristics of thinly-infilled rock joint surfaces were analyzed,joint surface damage with normal stress increases,the joint surface damage under normal stress mainly concentrated in the shear direction back slope,back slope surface and quartz sand crushed into powder,climbing the quartz sand concentration gradually,and the court to stress under the joint surface is smooth,basic as normal stress and certain infill thickness to asperity height ratio,the same joint surface damage,shows that the filling medium's contribution to the peak shear strength increased gradually;?3?In order to make up for the lack of observation of the interaction between the filling medium and the jointed rock wall in the laboratory test,the particle flow software PFC^2D was used to establish the same numerical model as the laboratory tests and conduct the direct shear tests under the same normal stresses.The shear strength characteristics of the jointed rock with thin layer filling were studied from the perspective of microscopy.Peak shear strength and the joint surface damage rule with the laboratory tests,and the boundary effect along with the increase of the joint surface roughness increased,the peak shear strength increase,along with the increase of infill thickness to asperity height ratio and weakened,the peak shear strength decreases,and the boundary effect on thin layer filling the influence of the peak shear strength of rock joints are mainly embodied in the joint plane JRC weakened;?4?Based on the results of laboratory tests and numerical tests,the shear strength criterion of thinly-infilled rock joints was established on the basis of considering the boundary effect and infill thickness to asperity height ratio,and is verified by the datas of laboratory tests.The results show that the predicted results of the new shear strength criterion for thinly-infilled rock joints are in good agreement with the experimental results,which preliminarily verify its rationality.