刚性挡墙后非饱和土破坏模式及主动土压力计算

目前主动土压力计算方法多仅针对土体处于饱和或干燥状态，忽略了其从非饱和到局部饱和，或饱和到非饱和的渐变过程，进而导致计算结果失真。鉴于此，首先开展了一系列刚性挡墙非饱和砂土主动土压力模型试验，揭示了墙后土体的破坏规律：（1）墙后土体顶部出现了近似竖直裂缝，且其发展深度随墙面粗糙度和含水率的增加而变大；（2）墙土界面摩擦对塑性区形状影响较小，且在挡墙移动过程中，墙后土体塑性区形状始终近似保持为平面。在试验基础上，引入广义有效应力原理，基于极限平衡分析建立了考虑吸应力效应的非饱和土主动土压力计算方法，理论与试验实测值表明，所提方法相比其他方法，更接近于试验值。分析了各主要因素对非饱和土压力分布规律的影响，结果表明：主动土压力随有效内摩擦角值增加而减少，而界面摩擦角对其分布影响较小；相比于无吸力情况，考虑吸力时主动土压力更小；随着进气值增加，吸应力对主动土压力的贡献减少，最终趋于恒定。

Failure mode and active earth pressure calculation of unsaturated soil behind rigid retaining wall

At present, the calculation methods of active earth pressure are mostly only for the soil in a saturated or dry state, ignoring the gradual process of soil from unsaturated to partially saturated, or from saturated to unsaturated, which leads to distortion of the calculation results. In this study, a series of model tests on the active earth pressure of unsaturated sand behind retaining wall is carried out to reveal the failure law of soil behind the wall. Observations show that, 1) there is an approximately vertical crack on the top of the soil behind the wall, and its development depth increases with the increase of wall surface roughness and water content; 2) the wall-soil interface friction has almost no effect on the plastic zone of the soil behind the wall, and the shape of the plastic zone remains approximately flat during the movement of the retaining wall. On the basis of tests, the generalized effective stress principle is introduced, an analytical method for calculating active earth pressure of unsaturated soil considering the effect of suction stress is developed based on limit equilibrium analysis. The theoretical and experimental results show that the proposed method is closer to the experimental values than other methods. Finally, the main factors influencing the active earth pressure of unsaturated soil are analyzed, and it is found that the active earth pressure decreases with the increase of soil friction angle, but the interface friction angle has little influence on the distribution of active earth pressure; compared with no suction case, the active earth pressure is smaller when considering suction; with the increase of air-entry value, the contribution of the suction stress to the active earth pressure decreases and eventually tends to be constant.