Study On Shear Characteristics Of Rock Joint Based On Barton Curve

The shear properties of rock joints play an extremely important role in the evaluation of geotechnical stability.At present,the study on shear properties of rock joints have been focused on medium and low normal stress conditions,and scholars have achieved many results.However,in nature,the stress state of rock joints is complex and diverse,and there are few studies on the mechanical shear properties of rock joints under high normal stress state,especially,there are fewer studies on shear properties of rock joints shears under large stress range(small stress?_n/JCS<0.3?medium stress 0.3<?_n/JCS<0.7?high stress 0.7<?_n/JCS).Based on Barton's classical curve and 3D printing technology,three kinds of sizes(100mm×100mm,200mm×200mm,300mm×300mm)rock joints were produced.A total of 93 group's joint samples were produced under three types roughness(JRC=1,JRC=11,JRC=19),and then the multi-layer geotechnical contact damage test system developed by the research group was used to carry out the direct shear test of rock joints under the full stress range and different sizes.And the relation between the shear properties of rock joints with normal stress,size,and roughness were analyzed.According to damaged area of rock joints classical shear strength criterions of rock joints are modified under low normal stress.The main conclusions are as follows:Firstly,based on the 3D printing technology of complex rock joints template,the rock joint samples with Barton classic curve surface morphology are produced.By comparing with the traditional rock joints sample produce process,the bubble of joints surface is less,production cycle of the sample is greatly reduced,and materials and expenses are saved.Secondly,Pixel Statistical Analysis(PSA)is used to obtain shear loss area after the shear failure of complex rock joints.It is concluded that the shear loss area of the rock joints increases with the increasing normal stress.under the same normal stress,shear loss area gradually increases with the JRC increasing.Shear area of the lower disc sample is larger upper disc sample.Thirdly,based on the real-time monitoring technology,the image of the rock joints after shear failure is analyzed.When?_n/JCS is less than 0.3,the rock joints is incompletely damaged;when?_n/JCS is greater than 0.3 and less than 0.7,completely shear damage of rock joints morphology are occurred;when?_n/JCS is greater than0.7,and the rock joints is collapse damage.Fourthly,the full-stress direct shear test of 300×300mm size rock joints shows that peak shear strength of rock joints has stress effect,which that is,the change ratio of peak shear strength and residual shear strength increased firstly,then stabilized,and finally decreased with increasing normal stress.Fifthly,the direct shear test of under large roughness(JRC=19)rock joints of three-size(100mm×100mm,200mm×200mm and 300×300mm)shows that the size effect 100mm×100mm to 300mm×300mm size is not obvious.Sixthly,the full stress range direct shear test of three kinds of roughness rock joints shows that the peak shear strength of the rock joint increases with the increasing of roughness under low normal stress(?_n/JCS less than 0.3).Finally,the shear strength criterion of Patton and Barton is modified based on the shear loss area of rock joint,and the modified formula considering the shear loss area is verified by comparing direct shear test.