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

Abstract

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.