The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are propose...The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are proposed for the damping modeling and its numerical implementation in distinct element analysis of rigid muhi-block systems.The stiff- ness proportional damping is constructed for the prescribed damping ratio,based on the non-zero fundamental frequency ef- fective during the time interval while the boundary conditions remain essentially constant.At this time interval,the funda- mental frequency can be estimated without complete eigenvalue analysis.The damping coefficients will vary while the damp- ing ratio remains the same throughout the entire analysis.A new numerical procedure is developed to prevent unnecessary energy loss that can occur during the separation phases.These procedures were implemented in the development of the dis- tinet element method for the dynamic analyses of piled multi-block systems.The analysis results |or the single-block and two-block systems were in a good agreement with the analytic predictions.Applications to the seismic analyses of piled four- block systems revealed that the new procedures can make a significant difference and may lead to much-improved results.展开更多
The reasonable design of protective structures to mitigate the hazards from rock fall depends on the knowledge of motion behaviors of falling stones,such as the falling paths,velocities,jump heights and distances.Nume...The reasonable design of protective structures to mitigate the hazards from rock fall depends on the knowledge of motion behaviors of falling stones,such as the falling paths,velocities,jump heights and distances.Numerical simulation is an effective way to gain such kind of knowledge,In this paper,the discontinuous deformation analysis (DDA) is applied to rock fall analysis.In order to obtain more reliable results,the following improvements and extensions are made on the original DDA.(1)Solve the problem of block expansions due to rigid body rotation error.(2) Add the function of modeling the drag resistance from air and plants so that the velocities of falling stones obtained by simulations are good enough in agreement with those by experiments in situ.(3)Add the capability to consider energy loss due to block collisions so that the jumping heights and distances obtained by simulations are good enough in agreement with thos by experiments even for the slope with very soft layer on its surface.One of application examples is presented to show that the extended DDA is very effective and useful in rock fall analysis.Therefore,the presented method is expected to be put into wide use in slop stability analysis.展开更多
在MTS815 Flex Test GT岩石力学试验系统上对大理岩在4级不同围压下进行试验,每级围压下分3级动应力进行循环加卸载,得到三轴应力状态下大理岩阻尼比和阻尼系数与不同应力状态之间的变化规律。通过试验发现:在同一级应力状态下岩石塑性...在MTS815 Flex Test GT岩石力学试验系统上对大理岩在4级不同围压下进行试验,每级围压下分3级动应力进行循环加卸载,得到三轴应力状态下大理岩阻尼比和阻尼系数与不同应力状态之间的变化规律。通过试验发现:在同一级应力状态下岩石塑性变形随着加载次数的增加逐渐增大,每次动循环岩石的能量耗散随着σmax/σc和围压σ3的增大而增大;同一级围压下,阻尼比和阻尼系数随着动应力振幅增大而递增,且随着围压的增大,递增的速率呈现出变快的趋势;在相同的σmax/σc下,阻尼比和阻尼系数随着围压的增大而递增,且随着σmax/σc的增大,递增的速率呈现出变快的趋势。岩石在高应力条件的循环荷载下,内部微裂纹扩展程度和新裂纹产生的数量和规模以及不可逆塑性变形更大,高应力水平下的每次循环荷载能量耗散也相应增加。展开更多
文摘The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are proposed for the damping modeling and its numerical implementation in distinct element analysis of rigid muhi-block systems.The stiff- ness proportional damping is constructed for the prescribed damping ratio,based on the non-zero fundamental frequency ef- fective during the time interval while the boundary conditions remain essentially constant.At this time interval,the funda- mental frequency can be estimated without complete eigenvalue analysis.The damping coefficients will vary while the damp- ing ratio remains the same throughout the entire analysis.A new numerical procedure is developed to prevent unnecessary energy loss that can occur during the separation phases.These procedures were implemented in the development of the dis- tinet element method for the dynamic analyses of piled multi-block systems.The analysis results |or the single-block and two-block systems were in a good agreement with the analytic predictions.Applications to the seismic analyses of piled four- block systems revealed that the new procedures can make a significant difference and may lead to much-improved results.
文摘The reasonable design of protective structures to mitigate the hazards from rock fall depends on the knowledge of motion behaviors of falling stones,such as the falling paths,velocities,jump heights and distances.Numerical simulation is an effective way to gain such kind of knowledge,In this paper,the discontinuous deformation analysis (DDA) is applied to rock fall analysis.In order to obtain more reliable results,the following improvements and extensions are made on the original DDA.(1)Solve the problem of block expansions due to rigid body rotation error.(2) Add the function of modeling the drag resistance from air and plants so that the velocities of falling stones obtained by simulations are good enough in agreement with those by experiments in situ.(3)Add the capability to consider energy loss due to block collisions so that the jumping heights and distances obtained by simulations are good enough in agreement with thos by experiments even for the slope with very soft layer on its surface.One of application examples is presented to show that the extended DDA is very effective and useful in rock fall analysis.Therefore,the presented method is expected to be put into wide use in slop stability analysis.
文摘在MTS815 Flex Test GT岩石力学试验系统上对大理岩在4级不同围压下进行试验,每级围压下分3级动应力进行循环加卸载,得到三轴应力状态下大理岩阻尼比和阻尼系数与不同应力状态之间的变化规律。通过试验发现:在同一级应力状态下岩石塑性变形随着加载次数的增加逐渐增大,每次动循环岩石的能量耗散随着σmax/σc和围压σ3的增大而增大;同一级围压下,阻尼比和阻尼系数随着动应力振幅增大而递增,且随着围压的增大,递增的速率呈现出变快的趋势;在相同的σmax/σc下,阻尼比和阻尼系数随着围压的增大而递增,且随着σmax/σc的增大,递增的速率呈现出变快的趋势。岩石在高应力条件的循环荷载下,内部微裂纹扩展程度和新裂纹产生的数量和规模以及不可逆塑性变形更大,高应力水平下的每次循环荷载能量耗散也相应增加。