水位骤变下土石坝非稳定渗流及稳定分析

Unsteady Seepage and Stability Analysis of Earth-Rock Dam Under the Rapid Changes of Reservoir Level

以库水位骤变全过程为分析工况,基于非稳定渗流理论,考虑渗透系数与基质吸力之间的非线性关系,研究了典型土石坝工程的非稳定渗流场变化规律和渗透稳定性,并对坝坡瞬态抗滑稳定系数进行了计算。结果表明:水位骤变过程中,坝体处于非稳定渗流状态,浸润线呈突起弯曲状并不断变化,且水位变化速率越快,弯曲越明显;水位骤升阶段,非稳定渗流场等势线整体向上游偏移,对应大坝典型部位的渗透坡降明显大于该水位时稳定渗流场的,且水位上升速率越大,渗透坡降越大,超过允许渗透坡降时可能发生渗透破坏;上游坝坡在非稳定渗流阶段的瞬态稳定安全系数变化较大,水位升高对其稳定有利,水位骤降超静孔隙水压力来不及消散,形成反向渗流,坝坡稳定性降低明显,且水位下降速率越大,稳定性越低。

Based on unsteady seepage theory,taking the rapid change process of reservoir level as working condition and considering the nonlinear relationship between permeability coefficient and the matrix suction,the change rule and variation law of unsteady seepage of a typical earth-rock dam was studied and the transient stability against sliding was calculated. The results show that the dam is in the unsteady seepage state with the change process of water level,so the dam seepage line is a protuberant,bent and changing curve,and the faster the change rate of water level is,the more obviously bending the curve is. In the stage of water rise,the equi-potential line of unsteady seepage field offset to the upstream than that of steady seepage field and the corresponding dam seepage gradient is significantly greater. The faster the water level rising rate is,the greater the seepage gradient is. Seepage failure may occur if it exceeds the allowable values. The transient stability safety coefficient is also changing a lot in the unsteady seepage phase. For upstream dam,the slope stability is increased with the higher water. Conversely it is reduced obviously in the dropping stage of water level,and the more decline rate of water level is,the faster the stability decreases,because it has not enough time to dissipate the excess pore water pressure and the reverse seepage is generated.