In Situ Monitoring Consolidation and Hardening Behaviors of an HDPE Geomembrane‐Cement‐Bentonite Composite Cutoff Wall

Vertical cutoff walls are commonly used for containment of contaminants and polluted groundwater. In this paper, an in situ multi‐parameter monitoring system that includes soil pressure, pore water pressure, and bulk electrical conductivity was installed in a 23.5‐m deep HDPE‐cement‐bentonite (HCB) cutoff wall, with the data collected from the first 20 d are presented herein. The shallow zone (≤2.5 m) became unsaturated after 2 d, triggering surface settlement, “CB mixture‐geomembrane” or “CB mixture‐trench sidewall” detachment, and shrinkage cracks; the intermediate zone (5–7.5 m) developed 80‐kPa suction on Day 4, while deeper responses lagged. Lateral pressure showed a V‐shaped trend, that is, initial hydration‐induced drop followed by a pressure increase due to bentonite swelling. Bulk electrical conductivity (3000–4000 mS/m) decreased overall but varied with the permeability of surrounding soil. The temperature evolution comprised three distinct stages: hydration heating, cooling, and stabilization.