Geosynthetic reinforcement and drainage in fine-grained embankments under rainfall

The increasing use of locally sourced fine-grained soils in embankment construction increases susceptibility to rainfall-induced instability due to low permeability, high water retention and limited shear strength. This study investigates the coupled reinforcement–drainage behaviour of geosynthetics in fine-grained embankments subjected to controlled rainfall infiltration. Laboratory-scale physical model tests were conducted to examine moisture migration, pore water pressure, earth pressure and deformation. Unreinforced slopes exhibited rapid infiltration with moisture contents increasing to 27.6–29.5% within the first hour. Reinforced slopes showed capillary barrier effects, causing transient moisture accumulation above reinforcement layers, while geocomposites provided effective lateral drainage, producing a pore pressure differential of 2.56 kPa, nearly three times that of geotextiles. Geocomposites reduced pore pressure rise by approximately 37% relative to unreinforced conditions and induced negative pressures beneath the reinforcement, indicating enhanced suction recovery and stress redistribution. Soil fines content strongly governed the hydraulic response where a 20% fines embankment showed rapid infiltration and low retention, whereas a ≥40% fines embankment retained over 50% moisture. The 20% fines embankment exhibited the largest crest settlement and localised toe failure. Numerical simulations reproduced the observed hydro-mechanical responses with minor deviations during post-rainfall dissipation, demonstrating that geocomposites significantly enhance the rainfall resilience and stability of fine-grained embankments.