Groundwater regime in a slope stabilised by drain trenches.

Drains are widely used in civil engineering as control works against slope instability in saturated clayey soils. The action of drains reduces pore pressures in the subsoil and consequently increases effective stresses and soil shear strength. Although drains are widely used in geotechnical design, their effect on slope stability is not fully understood and modeled. It is well known that the water table is subjected to broad variations due to atmospheric conditions and that the critical situation for slopes occurs during the wet season, when pore pressure in the subsoil attains its maximum. The real role of drains consists of avoiding this peak of pore pressure that could cause land sliding. Despite the behavior described, analyses proposed in the literature solve cases of drains working in slopes under steady hydraulic conditions at the boundaries. In this work we present a transient analysis of the phenomenon by considering the work of drain trenches in a transient regime due to variations in hydraulic conditions at the ground surface, as a consequence of rainfall. Under this hypothesis, the effect of drains is calculated to be greater than would be predicted by available design methods.