The sand-steel interface(SSI)behavior is crucial for the stability of offshore structures in marine environments.A series of cyclic and post-cyclic shear tests were conducted using a modified direct shear apparatus(MD...The sand-steel interface(SSI)behavior is crucial for the stability of offshore structures in marine environments.A series of cyclic and post-cyclic shear tests were conducted using a modified direct shear apparatus(MDSA),to examine both global and local SSI behaviors.Experimental visualization and image processing improvements enabled a comprehensive investigation of the influences of material properties and loading characteristics.Cyclic loading induced significant dilation-contraction alternations,with overall contraction predominating.Boundary conditions influenced the trends of cyclic shear stress,which stabilized after a specific loading cycles.Post-cyclic SSI exhibited notable dilation and stress-softening.Sands with improved gradation showed poor SSI strength development and more pronounced cyclic contraction.An optimal surface roughness for SSI strength develop-ment was identified.Dilation state lines,reflecting cyclic deformation,displayed a downward trend with pro-gressive loading cycles.Friction angles,affected by displacement amplitude,underwent a weakeningstrengthingstabilizing process with cumulated shear displacement.Shear band thicknesses,sensitive to normal stress,surface roughness,and displacement amplitude,gradually stabilized with increased shear displacement.Grain microstructure evolution during cyclic shearing depended on the initial sand fabric.Fine grains migrated and collapsed during cyclic loading,combined with grains lying down,lubricating sand-sand friction.Insignificant macro-micro changes in SSI with a smooth plate indicated only sliding motion occurring.展开更多
Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typi...Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.展开更多
基金the Natural Science of Jiangsu Province under Grant No BK20241527the Fundamental Research Funds for the Central Universities under Grant No B250201025the National Natural Science Foundation of China under Grant No 52309129.
文摘The sand-steel interface(SSI)behavior is crucial for the stability of offshore structures in marine environments.A series of cyclic and post-cyclic shear tests were conducted using a modified direct shear apparatus(MDSA),to examine both global and local SSI behaviors.Experimental visualization and image processing improvements enabled a comprehensive investigation of the influences of material properties and loading characteristics.Cyclic loading induced significant dilation-contraction alternations,with overall contraction predominating.Boundary conditions influenced the trends of cyclic shear stress,which stabilized after a specific loading cycles.Post-cyclic SSI exhibited notable dilation and stress-softening.Sands with improved gradation showed poor SSI strength development and more pronounced cyclic contraction.An optimal surface roughness for SSI strength develop-ment was identified.Dilation state lines,reflecting cyclic deformation,displayed a downward trend with pro-gressive loading cycles.Friction angles,affected by displacement amplitude,underwent a weakeningstrengthingstabilizing process with cumulated shear displacement.Shear band thicknesses,sensitive to normal stress,surface roughness,and displacement amplitude,gradually stabilized with increased shear displacement.Grain microstructure evolution during cyclic shearing depended on the initial sand fabric.Fine grains migrated and collapsed during cyclic loading,combined with grains lying down,lubricating sand-sand friction.Insignificant macro-micro changes in SSI with a smooth plate indicated only sliding motion occurring.
基金the support of the National Natural Science Foundation of China(Grant No.52108319)the Natural Science Foundation of Jiangxi Province(20224BAB214069)。
文摘Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.
