Abstract:
This paper presents a numerical study investigating the hydraulic response and stability of geosynthetic-reinforced
soil slopes subject to rainfall. A series of numerical simulations of unsaturated slopes with various
backfill–reinforcement–drainage systems subject to rainfall infiltration was performed by comprehensively
considering the combined effect of backfill (i.e., sand, silt, and silty clay), reinforcement type (i.e., geogrid or
nonwoven geotextile), and rainfall intensity (350 and 500 mm/day). The backfills were modeled using three
soil–water characteristic curves (SWCCs) representing the general suction range associated with sand, silt, and
clay. The influence of sand cushions in improving the stability of reinforced clay slopes was also assessed. The
numerical results reveal that the loss of matric suction and development of a capillary barrier effect within clay
backfills could have adverse impacts on both the global and local stabilities of the reinforced clay slopes. The
contribution of matric suction in enhancing slope stability was initially high for reinforced clay slopes; however,
the global stability of the reinforced clay slope substantially decreased due to the loss of matric suction as the
rainfall infiltration proceeded. The local instability of the geotextile-reinforced clay slope occurred due to the
capillary barrier effect at the geotextile–clay interface. The reinforced marginal soil slopes cannot effectively
drain the infiltrating water under torrential rainfall. Free drainage conditions may not be assumed for these
slopes if the drainage is not properly considered. Both the global and local factors of safety (FS) of the reinforced
sand slope were minimally influenced by the loss of matric suction induced by rainfall infiltration. The required
reinforcement tensile strengths for the reinforced silt and clay slopes to maintain FS=1.3 were, respectively,
approximately 3 and 4 times larger than that for reinforced sand slopes. Numerical results also indicated that the
inclusion of sand cushions, which provide both strength and drainage functions, can effectively enhance the
slope stability. An optimal sand cushion thickness of 15 cm (replacing 20% of marginal backfill with sand) was
determined in this study.
