考虑起始水力坡降的超固结土一维非线性固结分析

ONE-DIMENSIONAL NONLINEAR CONSOLIDATION ANALYSIS OF OVERCONSOLIDATED SOIL CONSIDERING THRESHOLD HYDRAULIC GRADIENT

考虑超固结黏性土中渗流存在的起始水力坡降及变荷载作用,建立超固结土一维非线性固结模型。利用连续条件建立固结模型的控制方程,并采用有限差分法求取该模型的数值解。在此基础上,当回弹再压缩指数ce等于压缩指数cc时,将该文差分解与考虑起始水力坡降的正常固结土非线性固结半解析解对比以验证该文解的可靠性。最后,分析起始水力坡降和超固结应力状态对黏性土固结性状的影响。结果表明：起始水力坡降导致土中超静孔压不能完全消散;当外荷载稳定值qu与起始水力坡降i0、水的重度γw及土层厚度H之积的比值小于1时,单面排水条件下渗流前锋不能至土层底面;起始水力坡降i0越大,土层沉降值越小,按孔压定义的土层平均固结度也越小;相同起始水力坡降下,超固结土层超静孔压的消散速率比正常固结土层快,超固结土层的最终沉降值小于正常固结土层,且前期固结压力越大则最终沉降量越小。

Considering threshold hydraulic gradient in the seepage of overconsolidated clay and time-dependent loading,the model for one-dimensional nonlinear consolidation of overconsolidated soil was developed. The governing equations for the model were obtained by means of continuity conditions,and the numerical solutions for the model were obtained by finite difference method. On that basis,when swelling index cebeing equaled to the compression index cc,the reliability of numerical solutions was verified by making a comparison between these solutions with semianalytical solutions for normal consolidated soil considering threshold hydraulic gradient. Finally,the effects of threshold hydraulic gradient and overconsolidated state on the consolidation behavior of clay were analyzed,and the results showed that the excess pore water pressure could not completely dissipated,which was resulted by the threshold hydraulic gradient. When the ratio of the final value of time-dependent load quto the product of threshold hydraulic gradient i0,the unit weight of water γwand the thickness of soil layer H was less than 1,the seepage boundary could not come to the bottom surface in the case of single drainage. Both the average degree of consolidation and the final settlement of soil layer decreased with increasing the value of threshold hydraulic gradient. With the same value of threshold hydraulic gradient,the dissipation rate of excess pore water pressure of overconsolidated soil layer was faster than that of normal consolidated soil layer,and the final settlement of overconsolidated soil layer was less than that of normal consolidated soil layer. The final settlement of overconsolidated soil layer decreased with increasing the preconsolidation pressure.