降雨入渗条件下非饱和土朗肯土压力分析

Rankine's earth pressure analysis of unsaturated soil under condition of rainfall infiltration

传统的土压力分析仅考虑了土体饱和强度对土压力产生的贡献,忽略了基质吸力及其变化对土压力的影响。运用非饱和土有效应力原理和饱和土朗肯土压力公式推导了非饱和土朗肯土压力公式,结合Iverson降雨入渗解析解,推导出降雨入渗条件下非饱和土压力公式。该公式将降雨入渗时的非饱和土压力表示为时间和深度的函数,更符合实际情况。研究结果表明:采用该方法计算得到的土压力值相对于传统计算结果偏大,作用点偏高;此外,随着降雨的发生、入渗和停止,主动土压力呈现"减小-增大-减小-稳定"趋势,被动土压力呈现"增大-减小-增大-稳定"趋势,该现象由降雨过程中基质吸力改变所致。由该公式获得的土压力分布及变化规律可用于挡土工程结构的设计。

The conventional earth pressure analysis method only considers the shear strength of saturated soil, which ignores the influence of matrix suction as well as its change. Based on the principle of effective stress of unsaturated soil and Rankine＇s earth pressure formula of saturated soil, the Rankine＇s earth pressure formula of unsaturated soil is deduced. The earth pressure formula of unsaturated soil under the condition of rainfall is established by the combination of the formula derived above and Iverson＇s rainfall infiltration analytical solution. In the formula, earth pressure of unsaturated soil under rainfall infiltration is expressed as a function of time and depth. The study result shows that the earth pressure value calculated by the improved method is relatively larger than the conventional calculation and its action point is higher. With the occurrence, infiltration and stop of rainfall, the value of active earth pressure is at a state of ＂decreasing, increasing, decreasing and lastly stable＂; but the value of passive earth pressure presents a tendency of ＂increasing, decreasing, increasing and stable＂. The phenomenon is due to the change of matrix suction during rainfall. The distribution and change rule of earth pressure calculated by the proposed formula can be applied to design of retaining engineering structure.