To study the influence of support timing and support strength on the mechanical properties and deformation damage characteristics of a single-sided unloaded rock mass,a true triaxial perturbation unloaded rock testing...To study the influence of support timing and support strength on the mechanical properties and deformation damage characteristics of a single-sided unloaded rock mass,a true triaxial perturbation unloaded rock testing system was used to conduct rock damage tests on sandstone with different support timing and strength paths.Based on the acoustic emission monitoring system,the spatial and temporal evolution characteristics of the whole process of rock body loaded instability under two stress paths were studied,and the mechanism of the reinforcing effect of stress support on the unloaded rock mass was analyzed.The results show that,within the scope of this study,both earlier applications of shoring and an increase in shoring strength can effectively improve the ultimate bearing capacity of the unloaded rock,which increases the ultimate bearing capacity of the unloaded rock mass by 60.31% and 54.96%,respectively;There is a phenomenon of rebound deformation of the rock mass during sudden changes in stress(single-sided unloading,stress support),which shows opposite expansion and compression platforms on the stress−strain curve;The crack evolution of unloaded rock under different stress support conditions shows the state law of"initial crack activation→middle steady state expansion→late main crack penetration",and the lagging support significantly accelerates the crack evolution from local activation to main penetration;The single-sided unloading and stress-supporting stages have less influence on the unloading deformationsσ_(1u),σ_(2u) and support deformationsσ_(1) t,σ_(2t) in theσ_(1) andσ_(2)directions,while they show significant response characteristics toσ_(3u),σ_(vu) and σ_(3) t,σ_(vt),and with the increase of the support strength,the stress-supporting stagesσ_(3) t,σ_(vt) gradually increase and exceed the deformations generated by the unloading stagesσ_(3u),σ_(vu);The increase of support strength can effectively compensate for the rock stress loss caused by unloading,which makes the maximum,minimum,and volumetric strain support coefficients during the loading and unloading of the rock body increase gradually while the effect on the intermediate principal strain support coefficient is small;During loading,the support strength of rock masses seeks a new bearing area by regulating stress equilibrium states.This process primarily manifests as a shift in the locations of the crushing zone and the main bearing area,accompanied by a corresponding transformation in failure patterns.Consequently,the rock mass transitions from asymmetric three-zone damage under no or weak support to approximate symmetric three-zone damage under strong support.Simultaneously,the main load-bearing area of the rock mass shifts from deep bearing in the unsupported to middle bearing under strong support as the support strength increases.展开更多
The rocks surrounding a roadway exhibit some special and complex phenomena with increasing depth of excavation in underground engineering.Quasi-static analysis cannot adequately explain these engineering problems.The ...The rocks surrounding a roadway exhibit some special and complex phenomena with increasing depth of excavation in underground engineering.Quasi-static analysis cannot adequately explain these engineering problems.The computational model of a circular roadway considering the transient effect of excavation unloading is established for these problems.The time factor makes the solution of the problem difficult.Thus,the computational model is divided into a dynamic model and a static model.The Laplace integral transform and inverse transform are performed to solve the dynamic model and elasticity theory is used to analyze the static model.The results from an example show that circumferential stress increases and radial stress decreases with time.The stress difference becomes large gradually in this progress.The displacement increases with unloading time and decreases with the radial depth of surrounding rocks.It can be seen that the development trend of unloading and displacement is similar by comparing their rates.Finally,the results of ANSYS are used to verify the analytical solution.The contrast indicates that the laws of the two methods are basically in agreement.Thus,the analysis can provide a reference for further study.展开更多
Rock burst is a kind of severe engineering disaster resulted from dynamic fracture process of rocks.The macrofailure behaviors of rocks are primarily formed after experiencing the initiation,propagation,and coalescenc...Rock burst is a kind of severe engineering disaster resulted from dynamic fracture process of rocks.The macrofailure behaviors of rocks are primarily formed after experiencing the initiation,propagation,and coalescenceof micro-cracks.In this paper,the grain-based discretized virtual internal bond model is employed to investigatethe fracturing process of unloaded rock under high in-situ stresses from the micro-fracture perspective.Thesimulated micro-fracturing process reveals that the longitudinal stress waves induced by unloading lead to thevisible unloading effect.The influences of in-situ stresses,mineral grain sizes,and grain heterogeneity on rockmacro and micro fracture are investigated.Micro-crack areas of tensile and shear cracks and micro-crack anglesare statistically analyzed to reveal the rock micro-fracture characteristics.The simulated results indicate thatthe combined effect of the stress state transition and the unloading effect dominates the rock unloading failure.The vertical and horizontal in-situ stresses determine the stress state of surrounding rock after unloading andthe unloading effect,respectively.As the vertical stress increases,the stress level after unloading is higher,andthe shear failure characteristics become more obvious.As the horizontal stress increases,the unloading effectincreases,leading to the intensification of tensile failure.The mineral grain size and grain heterogeneity alsohave nonnegligible influences on rock unloading failure.The micro-fracture perspective provides further insightinto the unloading failure mechanism of deep rock excavation.展开更多
基金Projects(2023 YFC 2907602,2022 YFF 1303302)supported by the National Key Research and Development Project of ChinaProject(52342404)supported by the National Natural Science Foundation of China+2 种基金Project(GXXT-2021-075)supported by the University Synergy Innovation Program of Anhui Province,ChinaProject(2022AH010053)supported by Excellent Scientific Research and Innovation Team of Universities in Anhui Province,ChinaProject(2022xscx080)supported by Anhui Provincial Department of Education Graduate Student Academic Innovation Fund,China。
文摘To study the influence of support timing and support strength on the mechanical properties and deformation damage characteristics of a single-sided unloaded rock mass,a true triaxial perturbation unloaded rock testing system was used to conduct rock damage tests on sandstone with different support timing and strength paths.Based on the acoustic emission monitoring system,the spatial and temporal evolution characteristics of the whole process of rock body loaded instability under two stress paths were studied,and the mechanism of the reinforcing effect of stress support on the unloaded rock mass was analyzed.The results show that,within the scope of this study,both earlier applications of shoring and an increase in shoring strength can effectively improve the ultimate bearing capacity of the unloaded rock,which increases the ultimate bearing capacity of the unloaded rock mass by 60.31% and 54.96%,respectively;There is a phenomenon of rebound deformation of the rock mass during sudden changes in stress(single-sided unloading,stress support),which shows opposite expansion and compression platforms on the stress−strain curve;The crack evolution of unloaded rock under different stress support conditions shows the state law of"initial crack activation→middle steady state expansion→late main crack penetration",and the lagging support significantly accelerates the crack evolution from local activation to main penetration;The single-sided unloading and stress-supporting stages have less influence on the unloading deformationsσ_(1u),σ_(2u) and support deformationsσ_(1) t,σ_(2t) in theσ_(1) andσ_(2)directions,while they show significant response characteristics toσ_(3u),σ_(vu) and σ_(3) t,σ_(vt),and with the increase of the support strength,the stress-supporting stagesσ_(3) t,σ_(vt) gradually increase and exceed the deformations generated by the unloading stagesσ_(3u),σ_(vu);The increase of support strength can effectively compensate for the rock stress loss caused by unloading,which makes the maximum,minimum,and volumetric strain support coefficients during the loading and unloading of the rock body increase gradually while the effect on the intermediate principal strain support coefficient is small;During loading,the support strength of rock masses seeks a new bearing area by regulating stress equilibrium states.This process primarily manifests as a shift in the locations of the crushing zone and the main bearing area,accompanied by a corresponding transformation in failure patterns.Consequently,the rock mass transitions from asymmetric three-zone damage under no or weak support to approximate symmetric three-zone damage under strong support.Simultaneously,the main load-bearing area of the rock mass shifts from deep bearing in the unsupported to middle bearing under strong support as the support strength increases.
基金supported by the National Natural Science Foundation of China (Nos.51479108 and 51174196)the National Basic Research Program of China (No.2014CB046300)+1 种基金Shandong University of Science and Technology (No.2012KYTD104)Research Start-up Project of Shandong University of Science and Technology (No.2015RCJJ061)
文摘The rocks surrounding a roadway exhibit some special and complex phenomena with increasing depth of excavation in underground engineering.Quasi-static analysis cannot adequately explain these engineering problems.The computational model of a circular roadway considering the transient effect of excavation unloading is established for these problems.The time factor makes the solution of the problem difficult.Thus,the computational model is divided into a dynamic model and a static model.The Laplace integral transform and inverse transform are performed to solve the dynamic model and elasticity theory is used to analyze the static model.The results from an example show that circumferential stress increases and radial stress decreases with time.The stress difference becomes large gradually in this progress.The displacement increases with unloading time and decreases with the radial depth of surrounding rocks.It can be seen that the development trend of unloading and displacement is similar by comparing their rates.Finally,the results of ANSYS are used to verify the analytical solution.The contrast indicates that the laws of the two methods are basically in agreement.Thus,the analysis can provide a reference for further study.
基金supported by the National Natural Science Foundation of China(Grant No.12302501)the China Postdoctoral Science Foun-dation(Grant No.2023MD744236)+4 种基金the Natural Science Basic Research Program of Shaanxi(Grant No.2024JC-YBQN-0061)the Postdoctoral Research Project of Shaanxi Province(Grant No.2023BSHEDZZ270)the Special Scientific Research Plan Project of Education Department of Shaanxi Provincial Government(Grant No.23JK0509)the Scientific Research Foundation for Excellent Returned Overseas Chinese Schol-ars funded by Shaanxi Provincial Government(Grant No.2023-021)the Innovation and Entrepreneurship Projects for College Students(Grant No.S202310703047).
文摘Rock burst is a kind of severe engineering disaster resulted from dynamic fracture process of rocks.The macrofailure behaviors of rocks are primarily formed after experiencing the initiation,propagation,and coalescenceof micro-cracks.In this paper,the grain-based discretized virtual internal bond model is employed to investigatethe fracturing process of unloaded rock under high in-situ stresses from the micro-fracture perspective.Thesimulated micro-fracturing process reveals that the longitudinal stress waves induced by unloading lead to thevisible unloading effect.The influences of in-situ stresses,mineral grain sizes,and grain heterogeneity on rockmacro and micro fracture are investigated.Micro-crack areas of tensile and shear cracks and micro-crack anglesare statistically analyzed to reveal the rock micro-fracture characteristics.The simulated results indicate thatthe combined effect of the stress state transition and the unloading effect dominates the rock unloading failure.The vertical and horizontal in-situ stresses determine the stress state of surrounding rock after unloading andthe unloading effect,respectively.As the vertical stress increases,the stress level after unloading is higher,andthe shear failure characteristics become more obvious.As the horizontal stress increases,the unloading effectincreases,leading to the intensification of tensile failure.The mineral grain size and grain heterogeneity alsohave nonnegligible influences on rock unloading failure.The micro-fracture perspective provides further insightinto the unloading failure mechanism of deep rock excavation.
