超静孔隙水压作用下软土卸荷模量研究

Study on the Unloading Modulus of Soft Soil under Excess Pore Water Pressure

软土的卸荷模量是基坑设计和数值分析的重要参数,然而现阶段富水软土地区的基坑开挖和设计均忽视了超静孔隙水压和卸荷比对软土卸荷模量的影响,导致基坑工程的数值分析结果与实际工程存在偏差。以深圳淤泥质软土为研究对象,利用TSZ全自动应力控制式三轴仪,开展一系列K0固结不排水三轴卸荷试验研究,求得不同超静孔隙水压和卸荷比条件下软土卸荷模量计算公式。研究结果表明,初始卸荷模量随固结围压增大而增大,超静孔隙水压对软土的卸荷模量具有削弱作用;以邓肯-张计算模型为基础,在考虑卸荷应力路径和超静孔隙水压对卸荷模量的影响下,推导出考虑卸荷应力路径的切线变形模量Et和考虑超静孔隙水压的切线变形模量Etu表达式;推导的软土卸荷模量公式对基坑的数值分析具有一定的实用价值。

The unloading modulus of soft soil is an important parameter in foundation pit design and numerical analysis.However,the influences of excess pore water pressure and unloading ratio on the unloading modulus of soft soil are ignored in foundation pit excavation and design in water-rich soft soil area,which results in the deviation between the numerical analysis results of foundation pit engineering and the actual engineering.A series of K0 consolidated undrained triaxial unloading tests were carried out using TSZ fully automatic stress-controlled triaxial apparatus for the study of silty soft soil in Shenzhen,to obtain the calculation formula of unloading modulus of soft soil under different conditions of excess pore water pressure and unloading ratio.The results show that the initial unloading modulus increases with the consolidation confining pressure increasing and the excess pore water pressure has a weakening effect on the unloading modulus of soft soil.Based on Duncan-Chang model,the tangent deformation modulus Etu considering unloading stress path and the tangent deformation modulus Etu considering excess pore water pressure are deduced.The formula of soft soil unloading modulus is of practical value to the numerical analysis of foundation pit.