变围压循环荷载作用下珠江三角洲软土动力特性试验研究

Experimental study on dynamic characteristics of soft soil in Pearl River Delta under cyclic confining pressure

列车循环荷载作用下软土地基产生较大沉降。以往动三轴试验模拟列车循环荷载时主要分析循环偏应力对软土动力特性的影响,而较少考虑循环围压的作用。基于此,采用GDS动三轴试验系统对珠江入海口饱和软土开展了一系列不排水变围压循环三轴试验,分析循环偏应力和循环围压耦合效应对饱和软土累积轴向应变、孔压以及阻尼比的影响。结果表明:累积轴向应变和归一化阻尼比随循环围压的增大而减小,最大孔压和最小孔压均随循环围压的增大而增大。当循环加载次数N=1 000,应力路径斜率η=0.33增长至η=1.00、2.00时,累积轴向应变ε_(p)=4.04%下降至ε_(p)=3.52%、2.45%,归一化阻尼比λ_(N)/λ_(1)=0.253相应变化为λ_(N)/λ_(1)=0.269、0.217,最大孔压由u_(max)=60.55 kPa分别增长至u_(max)=79.25和104.51 kPa,最小孔压由u_(min)=58.69 kPa分别增长至u_(min)=71.12和80.90 kPa。在此基础上,建立了饱和软土累积轴向应变计算模型,并进行了验证。

Large settlements of soft soil foundation occur under cyclic loading.The influence of cyclic deviatoric stress on the dynamic characteristics of soft soil has been previously analyzed using dynamic triaxial tests,while the effect of cyclic confining pressure has rarely been considered.In this study,a series of undrained dynamic triaxial tests with variable confining pressure were conducted for saturated soft soil from the Pearl River Delta using GDS dynamic triaxial test system.The coupling effects of cy‐clic deviatoric stress and confining pressure on the cumulative axial strain,pore pressure,and damping ratio were analyzed.The results show that the cumulative axial strain and normalized damping ratio de‐crease with the increase of the cyclic confining pressure,while the maximum and minimum pore pres‐sures increase with the increase of the cyclic confining pressure.When the number of cycles N=1 000and the stress path η increased from 0.33 to 1.00 and 2.00,the accumulated axial strain ε_(p) decreased from 4.04%to 3.52%and 2.45%,the normalized damping ratioλ_N/λ_(1 )from 0.253 to 0.269 and 0.217,the maximum pore pressure u_(max) increased from 60.55 kPa to 79.25 kPa and 104.51 kPa,and the mini‐mum pore pressure u_(min) increased from 58.69 kPa to 71.12 kPa and 80.90 kPa.Furthermore,a model for predicting the accumulated axial strain of saturated soft soil is established and verified.These results are helpful to deepen the understanding of the mechanical properties of soft clay under cyclic loading.