The beneficial role of stratigraphy on slope stabilization by drainage trenches: results of FEM numerical analyses.

Slope stabilization through drainage trenches is a classic approach in geotechnical engineering. Considering the low hydraulic conductivity of the soils in which this measure is usually adopted, a major constraint to the use of trenches is the time required to obtain a significant pore pressure decrease, here called “time lag”. In fact, especially when the slope safety factor is small, the use of drainage trenches may be a chancy approach due to the probability that slope deformations will damage the system well before it will become fully operative. However, this paper shows that the presence of persistent pervious natural soil layers in the slope can provide a significant benefit by increasing drainage efficiency and reducing time lag. As a matter of fact, any pervious layer that is intercepted by trenches may operate as part of the global hydraulic system, reducing the drainage paths. A simplified approach to design a drainage system accounting for the presence of a persistent pervious layer is proposed. This approach, which can exploit solutions available in literature for parallel drainage trenches, has been validated by numerical analyses.采用排水沟槽（drainage trenches）进行边坡加固是岩土工程领域的经典方法。考虑到该措施通常实施的土体水力传导率较低，采用排水沟槽的主要限制因素为实现显著孔隙水压力（pore pressure）下降所需的时长，该时长被称为‘时滞（time lag）’。事实上，尤其当边坡安全系数（slope safety factor）较小时，由于边坡变形可能在排水沟槽系统完全发挥效用前就将其破坏，采用排水沟槽并非稳妥方案。然而本文研究表明，边坡中存在的持久透水天然土层可通过提升排水效率、缩短时滞，发挥显著的加固增益效果。实际上，但凡被排水沟槽截断的透水层，均可作为整体水力系统的一部分发挥作用，缩短排水路径。本文提出了一种考虑持久透水天然土层存在的排水系统简化设计方法。该方法可借鉴已有文献中针对平行排水沟槽的求解方案，且已通过数值分析（numerical analyses）得到验证。