Abstract
Slope instability is often caused by decreases in suction due to heavy and prolonged rainfall. In this study, the application of capillary barrier systems (CBSs) for suction control and slope stabilization purposes (i.e. reducing the risk of rainfall-induced slope instabilities) is analysed, due to their capacity to limit the percolation of water into the underlying soil. The behaviour of two slopes was studied numerically: a bare slope made of fine-grained soil and the same slope covered by a capillary barrier system. The time evolution of suction in the slopes subjected to realistic atmospheric conditions was studied by performing numerical finite element analyses with Code_Bright. In particular, multi-phase multi-physics thermo-hydraulic analyses were performed, modelling the soil-atmosphere interaction over periods of many years. Suction and degree of saturation distributions obtained from these analyses were then exported to the software LimitState GEO, which was used to perform limit analysis to assess the stability of the slopes. The CBS was able to limit the percolation of water into the slope and was shown to be effective in increasing the minimum values of suction attained in the underlying ground, resulting in improved stability of the slope.
Highlights
In unsaturated conditions, the presence of matric suction s, defined as the difference between pore-liquid pressure pl and pore-gas pressure pg (i.e. s=pl-pg), imparts higher strength to the soil, compared to fully dry and fully saturated conditions
The new grid values of s·Sl were imported into computational limit analysis (LA) software to perform stability analyses considering the effect of unsaturated conditions on shear strength
Materials were modelled as rigid-perfectly plastic with Mohr-Coulomb yield criterion and associative plastic flow
Summary
The presence of matric suction s, defined as the difference between pore-liquid pressure pl and pore-gas pressure pg (i.e. s=pl-pg), imparts higher strength to the soil, compared to fully dry and fully saturated conditions. The barrier fails when the amount of water stored in the F.L. is so high that the suction at the interface between F.L. and C.L. decreases down to the “bulk water-continuity value” of the coarser layer, at which the hydraulic conductivity of the C.L. starts increasing significantly [5]. In this condition, water breakthrough occurs from the F.L. to the C.L., and eventually into the underlying soil
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