非饱和土本构模型在预测地表沉降中的应用

Application of unsaturated soil constitutive model to estimation of land subsidence

地下水位降低将导致非饱和土体中净平均应力和基质吸力发生变化,从而引起土体体积变化。利用GDS非饱和土三轴仪,研究了重塑非饱和黏土在干燥过程中试样含水率变化和总体积变化。针对某一典型基坑,运用大型有限元软件ABAQUS模拟了井点降水而形成的二维饱和-非饱和稳态渗流。饱和土区域和非饱和土区域沉降变形有着本质的区别,基于试验和数值模拟结果,根据Fredlund非饱和土弹性体变本构模型和饱和土有效应力原理,分别估算了饱和土区和非饱和土区沉降变形量。结果表明,在总沉降量中非饱和土区的沉降量是不可忽略的。随着降水深度的增大,非饱和土区域沉降量在总沉降量中所占比例将逐渐增大。

Drawdown of groundwater table causes the changes of net mean stress and matric suction in unsaturated soil, and then induces volume change of soil mass. By using the GDS unsaturated triaxial apparatus, the total volume change and water content change of the remoulded unsaturated soil in the test are studied in the drying process. For a typical foundation pit, ABAQUS is used to simulate two dimensional saturated-unsaturated steady-state seepage flows induced by foundation pit dewatering. Based on test and simulation results, using Fredlund constitutive model and effective stress theory, subsidences of unsaturated soil and saturated zones are estimated respectively for different drawdown depths. Computed results indicate that in total amount of subsidence, the portion of subsidence of unsaturated soil zone cannot be ignored. The contributions of unsaturated soil zone to total subsidence increases as drawdown depth increases.