Abstract The active earth pressure evaluation was typically conducted assuming dry backfills and/or two-dimensional collapse mechanisms. In practice, retained slope collapse usually shows a three-dimensional (3D) feature and soils are usually unsaturated. The present work develops a framework for evaluating the 3D active earth pressure under transient unsaturated flow conditions. The framework is implemented by using the kinematic approach of limit analysis, in conjunction with a closed-form solution for the transient unsaturated flow. Based on a 3D horn-like failure mechanism, the active earth pressure coefficient is determined. Results for three hypothetical soils of fine sand, silt, and clay are calculated. It emerges that the inclusion of 3D effects and unsaturated transient flow leads to a smaller active earth pressure coefficient. The 3D effects are mainly influenced by the width-to-height ratio of walls; several certain cases analyzed in this paper show that the difference in the active earth pressure coefficient with and without considering 3D effects can be as much as about 27% when the width-to-height ratio equates to 2, whereas this difference decreases to about 10% and 5% when the ratio reaches to 5 and 10. The contribution of transient flow is mainly affected by the soil types; considering the unsaturated flow effect in clay can approximately reduce the active earth pressure of 67%, whereas this difference corresponds to 34% and 22% in silt and fine sand. The obtained results can help to quantitatively understand changes in the active earth pressure due to 3D effects and the presence of transient infiltration.

中文翻译：

---

瞬态非饱和流动条件下的三维主动土压力

摘要 主动土压力评估通常是在假设干燥回填和/或二维坍塌机制的情况下进行的。在实践中，保留边坡坍塌通常显示三维 (3D) 特征，土壤通常是非饱和的。目前的工作开发了一个框架，用于评估瞬态非饱和流动条件下的 3D 主动土压力。该框架是通过使用极限分析的运动学方法结合瞬态非饱和流动的封闭形式解决方案来实现的。基于 3D 喇叭状破坏机制，确定主动土压力系数。计算了细砂、粉砂和粘土三种假设土壤的结果。结果表明，包含 3D 效应和非饱和瞬态流会导致较小的主动土压力系数。3D效果主要受墙壁宽高比的影响；本文分析的几个特定案例表明，当宽高比等于2时，考虑和不考虑3D效应的主动土压力系数的差异可高达27%左右，而该差异减小到10左右。 % 和 5%，当比值达到 5 和 10 时，瞬态流的贡献主要受土壤类型的影响；考虑到粘土中的非饱和流动效应，大约可以降低 67% 的主动土压力，而这一差异在粉砂和细砂中分别对应 34% 和 22%。获得的结果有助于定量了解由于 3D 效应和瞬态渗透的存在而导致的主动土压力的变化。