To reveal the mechanism of shear failure of en-echelon joints under cyclic loading,such as during earthquakes,we conducted a series of cyclic shear tests of en-echelon joints under constant normal stiffness(CNS)condit...To reveal the mechanism of shear failure of en-echelon joints under cyclic loading,such as during earthquakes,we conducted a series of cyclic shear tests of en-echelon joints under constant normal stiffness(CNS)conditions.We analyzed the evolution of shear stress,normal stress,stress path,dilatancy characteristics,and friction coefficient and revealed the failure mechanisms of en-echelon joints at different angles.The results show that the cyclic shear behavior of the en-echelon joints is closely related to the joint angle,with the shear strength at a positive angle exceeding that at a negative angle during shear cycles.As the number of cycles increases,the shear strength decreases rapidly,and the difference between the varying angles gradually decreases.Dilation occurs in the early shear cycles(1 and 2),while contraction is the main feature in later cycles(310).The friction coefficient decreases with the number of cycles and exhibits a more significant sensitivity to joint angles than shear cycles.The joint angle determines the asperities on the rupture surfaces and the block size,and thus determines the subsequent shear failure mode(block crushing and asperity degradation).At positive angles,block size is more greater and asperities on the rupture surface are smaller than at nonpositive angles.Therefore,the cyclic shear behavior is controlled by block crushing at positive angles and asperity degradation at negative angles.展开更多
A numerical analysis is presented for the oscillatory flow of Maxwell fluid in a rectangular straight duct subjected to a simple harmonic periodic pressure gradient.The numerical solutions are obtained by a finite dif...A numerical analysis is presented for the oscillatory flow of Maxwell fluid in a rectangular straight duct subjected to a simple harmonic periodic pressure gradient.The numerical solutions are obtained by a finite difference scheme method.The stability of this finite difference scheme method is discussed.The distributions of the velocity and phase difference are given numerically and graphically.The effects of the Reynolds number,relaxation time,and aspect ratio of the cross section on the oscillatory flow are investigated.The results show that when the relaxation time of the Maxwell model and the Reynolds number increase,the resonance phenomena for the distributions of the velocity and phase difference enhance.展开更多
Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint pe...Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions(initial normal stress,normal stiffness,shear velocity,and cyclic distance)influence it through cyclic shear tests under CNS conditions.The results revealed a through-going shear zone induced by cyclic loads,characterized by abrasive rupture surfaces and brecciated material.Key findings included that increased joint persistence enlarged and smoothened the shear zone,while increased initial normal stress and cyclic distance,and decreased normal stiffness and shear velocity,diminished and roughened the brecciated material.Shear strength decreased across shear cycles,with the most significant reduction in the initial shear cycle.After ten cycles,the shear strength damage factor D varied from 0.785 to 0.909.Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance.Low joint persistence,high initial normal stress,high normal stiffness,slow shear velocity,and large cyclic distance were the most destabilizing combinations.Cyclic loads significantly compressed en-echelon joints,with compressibility highly dependent on normal stress and stiffness.The frictional coefficient initially declined and then increased under a rising cycle number.This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.42172292)Taishan Scholars Project Special Funding,and Shandong Energy Group(Grant No.SNKJ 2022A01-R26).
文摘To reveal the mechanism of shear failure of en-echelon joints under cyclic loading,such as during earthquakes,we conducted a series of cyclic shear tests of en-echelon joints under constant normal stiffness(CNS)conditions.We analyzed the evolution of shear stress,normal stress,stress path,dilatancy characteristics,and friction coefficient and revealed the failure mechanisms of en-echelon joints at different angles.The results show that the cyclic shear behavior of the en-echelon joints is closely related to the joint angle,with the shear strength at a positive angle exceeding that at a negative angle during shear cycles.As the number of cycles increases,the shear strength decreases rapidly,and the difference between the varying angles gradually decreases.Dilation occurs in the early shear cycles(1 and 2),while contraction is the main feature in later cycles(310).The friction coefficient decreases with the number of cycles and exhibits a more significant sensitivity to joint angles than shear cycles.The joint angle determines the asperities on the rupture surfaces and the block size,and thus determines the subsequent shear failure mode(block crushing and asperity degradation).At positive angles,block size is more greater and asperities on the rupture surface are smaller than at nonpositive angles.Therefore,the cyclic shear behavior is controlled by block crushing at positive angles and asperity degradation at negative angles.
基金Project supported by the National Natural Science Foundation of China(Nos.11672164 and41831278)the Taishan Scholars Project Foundation of Shandong Province of China
文摘A numerical analysis is presented for the oscillatory flow of Maxwell fluid in a rectangular straight duct subjected to a simple harmonic periodic pressure gradient.The numerical solutions are obtained by a finite difference scheme method.The stability of this finite difference scheme method is discussed.The distributions of the velocity and phase difference are given numerically and graphically.The effects of the Reynolds number,relaxation time,and aspect ratio of the cross section on the oscillatory flow are investigated.The results show that when the relaxation time of the Maxwell model and the Reynolds number increase,the resonance phenomena for the distributions of the velocity and phase difference enhance.
基金funded by the China Scholarship Council(CSC.202006220274).
文摘Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions(initial normal stress,normal stiffness,shear velocity,and cyclic distance)influence it through cyclic shear tests under CNS conditions.The results revealed a through-going shear zone induced by cyclic loads,characterized by abrasive rupture surfaces and brecciated material.Key findings included that increased joint persistence enlarged and smoothened the shear zone,while increased initial normal stress and cyclic distance,and decreased normal stiffness and shear velocity,diminished and roughened the brecciated material.Shear strength decreased across shear cycles,with the most significant reduction in the initial shear cycle.After ten cycles,the shear strength damage factor D varied from 0.785 to 0.909.Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance.Low joint persistence,high initial normal stress,high normal stiffness,slow shear velocity,and large cyclic distance were the most destabilizing combinations.Cyclic loads significantly compressed en-echelon joints,with compressibility highly dependent on normal stress and stiffness.The frictional coefficient initially declined and then increased under a rising cycle number.This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.
