Numerical models for 2D free boundary analysis of groundwater in slopes stabilized by drain trenches.

A numerical model for 2D free boundary analysis of groundwater in slopes stabilized by drain trenches has been developed. It consists of a fronttracking method (based on an original way of adapting the space derivatives), very effective in saving calculation time respect to classical fix-grid methods. The method analyses the trenches effect inside slopes in which the soils above the water table are partially saturated, for which a boundary can be recognized between the saturated domain (water table) and the unsaturated one (above the water table). In this case pore pressure lowering, due to trenches, can be analyzed considering the progressively reduction of the saturated domain. This approach efficiently solves the problem of fixing hydraulic boundary conditions on the sides of the trenches. Results have been compared with those obtained by a fix-grid method, observing difference less than 0.14%. Applying the method, the capability of drain trenches to control the effect of heavy rainfalls has been investigated, calculating (during the transient process of water table lowering) limit values of water recharge for which water table keeps on constant.