Internal erosion has been widely observed in geomaterials, resulting in many instability problems. However, there is little experimental research concerning mechanisms of internal erosion under oscillating hydraulic gradient resulting from storm surges and waves, which can be induced by extreme events and climate change. A series of laboratory seepage experiments on gap-graded sand specimens was conducted under a compound seepage mode including monotonic and sinusoidal cyclic hydraulic gradients, which were characterized by real-time permeability measurements and particle image velocimetry (PIV). The results show that a cyclic hydraulic gradient can initiate unclogging in previously clogged specimens and erosion in unstable specimens without reaching the critical hydraulic gradient. Increasing the inflow loading frequency from 0.005 to 0.02 Hz resulted in an increase in the final permeability, with all changing patterns affected by cyclic pore-throat narrowing and pore-throat reopening. The permeability evolution, fine-particle PIV, and fine-particle distribution showed good agreement, indicating that the effects of unclogging and erosion decrease with the progression of inflow loading cycles. Recent developments in laboratory testing and imaging analysis were combined to offer a comprehensive understanding of permeability evolution in gap-graded sand, which is relevant to climate change mitigation and adaptation of geotechnical structures.
Yuliang Guo, Budi Zhao, Xueyu Geng et al.· Journal of Geotechnical and...· 0 citations
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.
Lihua Li, Han Zhou, Xunchang Fei et al.· Geotechnical Engineering· 0 citations