非稳定渗流作用下非饱和土朗肯土压力分析

Unsaturated Rankine soil pressure analysis under unsteady seepage

摘要:

含水量变化会引起土体力学特性的改变,现有的工程中所采用的土压力计算理论仍然以饱和土理论为主,为研究渗流影响下非饱和土土压力变化,基于动态土水特征曲线,考虑非稳定渗流,对渗流过程中的Richards方程进行求解,得到了考虑动态土水特征曲线情况下吸力的理论解,并对吸力分布规律进行分析。基于动态效应下吸力的理论解,推导了渗流影响下非饱和土朗肯土压力方程,基于所得的土压力方程分析了动态效应对非饱和土压力分布的影响；将所得土压力理论解用于分析基坑支护结构,利用数值软件模拟不同的降雨强度入渗过程中支护结构土压力的变化；基于非饱和土理论计算了基坑支护结构的安全系数。结果表明:动态效应下主动土压力增加,被动土压力减小,吸力越大,土压力差别越明显；降雨入渗条件下,动态效应支护结构受到的主动土压力会明显小于静态效应,且入渗速率越大,土压力差值越明显；非饱和土理论计算的安全系数高于饱和土。考虑动态效应影响后安全系数有所下降,说明降雨入渗将增加基坑失稳的风险。

Abstract:

Changes in water content alter soil mechanical properties. Current engineering theories for earth pressure calculation mainly use saturated soil theory. This study investigates unsaturated soil pressure under seepage effects with dynamic soil-water characteristic curves. Unsteady seepage is considered. The Richards equation during seepage process is solved. A theoretical solution for suction considering dynamic soil-water characteristic curves is obtained. Suction distribution patterns are analyzed. Using the suction solution with dynamic effects, the Rankine earth pressure equation for unsaturated soil under seepage is derived. The equation helps analyze dynamic effects on unsaturated soil pressure distribution. The theoretical earth pressure solution is applied to foundation pit support structures. Numerical software simulates earth pressure changes on support structures during rainfall infiltration with different intensities. Safety factors of support structures are calculated using unsaturated soil theory. Results show: Dynamic effects increase active earth pressure and decrease passive earth pressure. Larger suction leads to more significant differences. Under rainfall infiltration, dynamic effects make active earth pressure on support structures smaller than static effects. Faster infiltration rates cause greater pressure differences. Safety factors calculated by unsaturated soil theory exceed those by saturated soil theory. Considering dynamic effects reduces safety factors, indicating rainfall infiltration increases foundation pit instability risks.