首页|Shear failure behaviors and degradation mechanical model of rockmass under true triaxial multi-level loading and unloading shear tests
Shear failure behaviors and degradation mechanical model of rockmass under true triaxial multi-level loading and unloading shear tests
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The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under 2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stress σn and lateral stressσp to investigate the shear strength,deformation,and failure characteristics.The results indicate that under different σn and σp,the stress-strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure sur-face roughness almost linearly increase with the increase in σn,while they first increase and then grad-ually decrease as σp increases,with the maximum increases of 12.9％for strength and 15.1％for roughness.The shear residual strength almost linearly increases with σn,but shows no significant change with σp.Based on the acoustic emission characteristic parameters during the test process,the shear frac-ture process and microscopic failure mechanism were analyzed.As the shear stress τ increases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by micro-scopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion cjp,friction angle φjp,and dilation angle φjp during rockmass shear fracture process were studied.Under different σn and σp,G first rapidly decreases and then tends to stabilize;cjp,φjp,and Ψjp first increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on 3D discrete element software.The proposed model effectively simulates the shear failure evolution pro-cess of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.
State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures,Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education,College of Civil Engineering and Architecture,Guangxi University,Nanning 530004,China
State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China
China Energy Engineering Group Guangxi Electric Power Design Institute Co.Ltd.,Nanning 530007,C
State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering,China University of Mining and Technology,Xuzhou 221116,China
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