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