Coupled hydro-mechanical analysis of the effects of medium depth drainage trenches mitigating deep landslide activity

Mitigation measures aimed at reducing the landslide hazard often consists of drainage systems, in particular when the piezometric regime in the slope is identified as an internal factor predisposing the landslide to fail, the latter is very often the case when weather-induced landslides are dealt with. In the past such mitigation measure has been considered eligible solely for shallow landslide mechanisms. However, some authors have reported that the variation in piezometric regime at large depth becomes no more negligible if a medium depth drainage trench system is installed. Nonetheless, the efficacy of a drainage trench system is often hard to quantify because of the high-level computation process that needs to be undertaken, since it has to include, in principle, several parameters describing the saturated-partially saturated hydro-mechanical behaviour of the material as well as all the processes occurring when interacting with the vegetation and the weather; this is even more complicated due to the geological history and the resulting geo-hydro-mechanical (GHM) context to deal with. As such, the determination of the efficiency of a drainage system represents still an open issue in the engineering practice, since this issue relates to a transient hydro-mechanical (HM) boundary value problem. Very often the design of such mitigation measures has been pursued by using design-charts determined under simplified hypotheses. In this paper, the effects of implementing the geological history of the slope of reference, representative of a widely spread landslide mechanism type across the GHM context dealing with, have been investigated on the drains-induced transient seepage, being computed by means of advanced fully coupled two-dimensional HM numerical modelling. The HM numerical analyses reported in this contribution address to a reference case study in the Eastern sector of the Southern Apennines region, which has been selected as prototype landslide in the assessment of the stabilization efficacy of deep drainage trench systems.