| In all rock mass engineering,it is very important to determine the shear strength of joint surface accurately and reliably for evaluating the stability and safety of rock mass engineering.A clear understanding of the shear mechanism of joint surface and quantitative evaluation of its roughness are the basis to determine the shear strength of joint.As the basic and core research topics in the field of rock mass engineering,these two research contents have always attracted attention from domestic and foreign scientists in recent decades.Based on the above research objectives,this thesis aims to comprehensively reveal the macroscopic and microscopic shear mechanisms of joint surface.What is more,this thesis aims to puts forward systematic evaluation methods of joint roughness considering shear failure mechanism and prediction model of shear strength.This can provide a reliable scientific basis for further quantifying the strength of jointed rock mass.Based on laboratory physical tests and numerical simulation test methods,the direct shear tests of Barton's typical joints,joints with different protrusions,and natural rough joints under different normal stresses and shear directions were carried out successively in this paper.The change law of shear stress was analyzed and the macro and micro failure mechanism of joint surface in the shear process was described and summarized.What is more,the weakening mechanism of joint roughness was quantitatively discussed.Since we had a clear understanding of the progressive failure mechanism of joint surfaces,a new statistical parameter,weighted positive angle WR+ was proposed to describe the roughness of the two-dimensional joint profile using mathematical statistics method.The shear direction and protrusion contribution are both considered in the definition of WR+.The function relationship between WR+and JRC2d was established,and its rationality was verified based on the rough morphology of natural joint surface.Then,the roughness evaluation method of two-dimensional joint profile was extended to the case of three-dimensional j oint surface and a new method to determine the roughness of j oint surface was proposed.In addition,new prediction models of shear strength considering the influence of sampling interval was proposed.Finally,the size effect and anisotropy of roughness and shear strength of large natural joint surface were analyzed in detail based on the research results of this paper.(1)Based on 3D printing and 3D modeling technology,Barton typical joint samples with the same morphology were fabricated.Then,the shear mechanical behavior of rough joints under different normal stress and shear directions was systematically studied based on the laboratory physical test.First,the macro mechanical characteristics of 10 rock joints with different roughness were systematically analyzed by shear stress and normal displacement.Secondly,the effects of normal stress,joint roughness and shear direction on the micro failure mechanism of joint surface during shear were analyzed by failure diagram of j oint specimen.Finally,the whole and local weakening mechanism of joint surface roughness before and after shear was quantitatively analyzed by using three-dimensional scanning technology.(2)The direct shear tests of j oint specimens under constant normal stress were successfully simulated by particle flow software PFC.Then,the shear mechanical behaviors of Barton typical joints and regular teeth joints with different protrusions were discussed in detail.First,the effects of rough morphology and external normal stress on the variation of shear strength in joints were analyzed separately,and the mutual variation relationship between shear stress and crack development during shear process was revealed.With the help of crack tracking module and force chain analysis,the failure order and scale of different morphologies in joint surface during shear process were described in detail.Then,the variation law of the average stress at different protrusions in joint surface during shear process was quantitatively analyzed by measuring circle function.Furthermore,the contribution of the joint protrusions with different sizes to the overall roughness was analyzed,and the progressive failure mechanism of the joint surface in the shear process was revealed.(3)The 10 typical joints proposed by Barton are commonly used in engineering.According to the data of laboratory direct shear test,the JRC2d values of 10 typical j oints were corrected and supplemented in direction 1 and direction 2 with the help of JRC-JCS model.Then,the correlations between the existing statistical parameters and new JRC2d values were verified based on 10 typical joints.Based on the new understanding of the shear failure mechanism of joints in physical and numerical experiments,the shear failure models of rough joints under different normal forces were summarized.Then,a new statistical parameter WR+,which can consider both the shear direction and the contribution of joint protrusions was proposed.Next,the functional relationships between WR+and JRC2d were established under 5 sampling intervals.In addition,the influence of sampling interval was discussed.Finally,the anisotropy of joint surface roughness was discussed by using WR+based on the 3D scanning data of 5 natural joint surface,which preliminarily verified the rationality and practicability of WR+.(4)Based on five natural rough rock joint surfaces,several natural joint samples with the same morphology were fabricated with the help of 3D scanning,3D printing and 3D modeling technology,and the laboratory direct shear tests were carried out under four shear directions and four normal stress conditions.Firstly,the influence of shear direction and normal stress on shear stress and failure characteristics of natural rock joint surface was discussed.Based on the new evaluation method of joint profile roughness(JRC2d),the existing arithmetic average method and the new weighted average method proposed in this paper were used to predict the roughness of natural joint surface(JRC3d)in different directions.Then,the advantages of the weighted average method are verified.Finally,the weakening rules of different roughness in natural joint surface were quantitatively analyzed by using the roughness indexes JRC2d and JRC3d,and the influence mechanism of different shear directions and normal stress was discussed.(5)The JRC-JCS model proposed by Barton had been improved by the new three-dimensional roughness evaluation method proposed in this paper.Five prediction models of shear strength of j oint surface under different sampling intervals were proposed and the accuracy of the model was verified by the indoor physical test data.The morphological data of two large natural joint surfaces were obtained and divided into several joint surfaces with different sizes.The roughness and shear strength of joints with different sizes in different shear directions were quantitatively evaluated by the new method proposed in this paper.Then,the size effect of roughness and shear strength of j oints with different sizes were discussed in detail.What is more,the anisotropy of roughness and shear strength for joint surface was analyzed quantitatively with the help of standard deviation. |
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