降雨入渗条件下非饱和膨胀土边坡原位监测

Artificial rainfall infiltration tests on a well-instrumented unsaturated expansive soil slope

为了对降雨诱发的非饱和膨胀土边坡失稳的机理有较深入的了解,在湖北枣阳选取了一个11 m高的典型的非饱和膨胀土挖方边坡进行人工降雨模拟试验和原位综合监测。监测成果表明:降雨入渗造成2 m深度以内土层中孔隙水压力和含水量大幅度增加,致使膨胀土体的抗剪强度由于有效应力的减少及土体吸水膨胀软化而降低;同时,降雨入渗造成土体中水平应力与竖向应力比显著增加,并接近理论的极限状态应力比,以致软化的土体有可能沿着裂隙面发生局部被动破坏,此破裂面在一定条件下(如持续降雨条件下)可能会逐渐扩展,最后发展成为膨胀土中常见的渐进式滑坡。

To improve our understanding of the fundamental mechanism of rain-induced landslides in unsaturated expansive soils, artificial rainfall simulation tests were carried out on an 11 m high cut slope in a typical medium-plastic expansive clay in Hubei of China. The slope was well-instrumented with tensiometers, thermal conductivity suction sensors, moisture probes, earth pressure cells, inclinometers, a tipping bucket rain gauge, a vee-notch flow meter and an evaporimeter. Two artificial rainfall events were created during a month of field investigation and monitoring. Monitored results demonstrate: rainfall infiltration leads to a significant increase in pore-water pressure and water content within the top 2 m soil layer, which may result in a reduction of shear strength due to a decrease in effective stress and wetting-induced softening. On the other hand, rainfall infiltration causes a significant increase in total stress ratio (sh/sv), which may lead to a local passive failure and then trigger a progressive slope failure under a continuous rainfall condition.