SOIL-CEMENT-BENTONITE CUTOFF WALL FOR SEEPAGE REMEDIATION AT THE CONDUIT-EMBANKMENT CONTACT ZONE

Abstract

Seepage concentrated along the conduit–embankment contact zone is a critical dam safety problem because this interface is prone to preferential flow and is difficult to treat reliably under constrained construction conditions. This study investigates the use of a soil-cement-bentonite (SCB) cutoff wall as a practical and field-verifiable remedial measure for this type of seepage problem at Da Si Dam, Lam Dong Province, Vietnam. Site investigation and quality verification during construction identified a high-permeability band adjacent to the outlet conduit. In response, an SCB cutoff wall was constructed parallel to the conduit on the downstream side under bentonite slurry support. The adopted backfill, consisting of local soil, 7% bentonite, 2% cement, and a superplasticizer, was selected through laboratory trial testing to achieve both low hydraulic conductivity and adequate workability for trench placement. Post-construction in-situ borehole permeability tests yielded hydraulic conductivity values from 8.93×10⁻⁷ to 3.56×10⁻⁶ cm/s, all below the design criterion of k ≤ 1×10⁻⁵ cm/s. Subsequent field inspections during reservoir operation showed no visual evidence of seepage, localized wetting, or abnormal moisture on the downstream slope surface above and adjacent to the treated conduit zone, confirming the effectiveness of the SCB cutoff wall for remediation of this difficult soil–structure contact zone.