Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suct...Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.展开更多
The pressure evolution associated with the transient shock-induced infiltration of gas flow through granular media consisting of mobile particles is numerically investigated using a coupled Eulerian–Lagrangian approa...The pressure evolution associated with the transient shock-induced infiltration of gas flow through granular media consisting of mobile particles is numerically investigated using a coupled Eulerian–Lagrangian approach.The coupling between shock compaction and interstitial flow has been revealed.A distinctive two-stage diffusing pressure field with deflection occurring at the tail of the compaction front is found,with corresponding spikes in both gaseous velocity and temperature profiles emerging within the width of the compaction front.The compaction front,together with the deflection pressure,reaches a steady state during the later period.An analytical prediction of the steady deflection pressure that considers the contributions of porosity and the non-isothermal effect is proposed.The isothermal single-phase method we developed,combining the porosity jump condition across the compaction front,shows consistent pressure evolution with the non-isothermal CMP-PIC one under weak shock strength and low column permeability.Lastly,the microscale mechanism governing the formation of not only pressure deflection but also gaseous velocity and temperature spikes within the width of the compaction front has been described.These aforementioned evolutions of the flow field are shown to arise from the nozzling effects associated with the particle-scale variations in the volume fraction.展开更多
Residual stress originated from thermal expansion mismatch determines the mechanical properties of ceramic matrix composites(CMCs).Here,continuous SiC fiber reinforced SiC matrix(SiC_(f)/SiC)composites were fabricated...Residual stress originated from thermal expansion mismatch determines the mechanical properties of ceramic matrix composites(CMCs).Here,continuous SiC fiber reinforced SiC matrix(SiC_(f)/SiC)composites were fabricated by nano-infiltration and transient eutectic-phase(NITE)method,and the residual stress of the composites was investigated using high-temperature Raman spectrometer.With temperature increasing from room temperature to 1400℃,the residual stresses of the matrix and the fiber decrease from 1.29 to 0.62 GPa and from 0.84 to 0.55 GPa in compression respectively,while that of the interphase decreases from 0.16 to 0.10 GPa in tension.The variation of residual stress shows little effect on the tensile strength of the composites,while causes a slight decrease in the tensile strain.The suppression of fiber/matrix debonding and fiber pulling-out caused by the residual stress reduction in the interphase is responsible for the decreasing tensile strain.This work can open up new alternatives for residual stress analysis in CMCs.展开更多
基金Projects(51508040,51578079,51678074,51678073)supported by the National Natural Science Foundation of ChinaProject(KFJ160601)supported by the Open Fund of Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province(Changsha University of Science and Technology),China
文摘Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.
基金supported by National Natural Science Foundation of China(Grants No.11972088,No.12122203).
文摘The pressure evolution associated with the transient shock-induced infiltration of gas flow through granular media consisting of mobile particles is numerically investigated using a coupled Eulerian–Lagrangian approach.The coupling between shock compaction and interstitial flow has been revealed.A distinctive two-stage diffusing pressure field with deflection occurring at the tail of the compaction front is found,with corresponding spikes in both gaseous velocity and temperature profiles emerging within the width of the compaction front.The compaction front,together with the deflection pressure,reaches a steady state during the later period.An analytical prediction of the steady deflection pressure that considers the contributions of porosity and the non-isothermal effect is proposed.The isothermal single-phase method we developed,combining the porosity jump condition across the compaction front,shows consistent pressure evolution with the non-isothermal CMP-PIC one under weak shock strength and low column permeability.Lastly,the microscale mechanism governing the formation of not only pressure deflection but also gaseous velocity and temperature spikes within the width of the compaction front has been described.These aforementioned evolutions of the flow field are shown to arise from the nozzling effects associated with the particle-scale variations in the volume fraction.
基金financial support of the research grant from National Natural Science Foundation of China (No.51902328)the research grant from Science and Technology Commission of Shanghai Municipality (No. 19ZR1464700)the research grant from Key Program of the Chinese Academy of Sciences (No.ZDRW-CN2017-1)
文摘Residual stress originated from thermal expansion mismatch determines the mechanical properties of ceramic matrix composites(CMCs).Here,continuous SiC fiber reinforced SiC matrix(SiC_(f)/SiC)composites were fabricated by nano-infiltration and transient eutectic-phase(NITE)method,and the residual stress of the composites was investigated using high-temperature Raman spectrometer.With temperature increasing from room temperature to 1400℃,the residual stresses of the matrix and the fiber decrease from 1.29 to 0.62 GPa and from 0.84 to 0.55 GPa in compression respectively,while that of the interphase decreases from 0.16 to 0.10 GPa in tension.The variation of residual stress shows little effect on the tensile strength of the composites,while causes a slight decrease in the tensile strain.The suppression of fiber/matrix debonding and fiber pulling-out caused by the residual stress reduction in the interphase is responsible for the decreasing tensile strain.This work can open up new alternatives for residual stress analysis in CMCs.
