Seepage Barrier Mix Design Development, Installation, and Evaluation-Paper

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The paper describes the design, field adjustment, and evaluation of a self-hardening slag cement–bentonite seepage barrier installed along 4,700 feet of alignment to contain contaminated groundwater. The wall extended 20–85 feet deep through variable soils, including cobbles and boulders, under challenging access and groundwater conditions.<br /><br />Preconstruction laboratory testing considered site soils, groundwater dilution, acidic and sulfate-rich groundwater, strength, permeability, slurry stability, and set time. The selected mix used slag, Portland cement, bentonite, and a polymer retarder. Its target performance was an unconfined compressive strength (UCS) of 50–300 psi and hydraulic conductivity no greater than 5 × 10⁻⁷ cm/s at 28 days.<br /><br />Field conditions differed from laboratory assumptions. High groundwater flows diluted the slurry, reducing strength and increasing permeability; lowering the water-to-cementitious-material ratio improved performance. Difficult excavation also extended panel installation times, risking premature setting. Polymer dosage was therefore adjusted to maintain workability, with careful control needed because excess retarder delayed strength gain and permeability reduction.<br /><br />The project relied on routine slurry quality-control tests and laboratory strength and permeability results at early curing ages. These indicators enabled adjustments before 28-day results were available. Testing showed a direct relationship between strength and permeability: for the final field-adjusted mix, UCS above approximately 70 psi generally corresponded to permeability meeting the project limit. Early results could therefore help predict final performance.<br /><br />The authors conclude that thorough preconstruction testing is valuable but cannot fully anticipate subsurface variability or installation difficulties. Mix design should account for the construction method, and contractors should continuously interpret field and laboratory data, maintain a performance margin, and adjust proportions as needed. Where samples initially fail specifications, extended curing and retesting may be appropriate, depending on project risk and design intent.

Keywords

slag cement-bentonite barrier

seepage wall

groundwater containment

hydraulic conductivity

unconfined compressive strength

polymer retarder

slurry stability

field adjustment

permeability

bentonite slurry