Laboratory evaluation and field observations of plastic-concrete cutoff walls for seepage control in earth-dam foundations

Plastic-concrete cutoff walls require low hydraulic conductivity and sufficiently low stiffness, and the wall must accommodate foundation deformation. Twenty-five laboratory mixtures of Type V Portland cement, sodium bentonite, water, and graded aggregates with a 16 mm nominal maximum size were evaluated. The study measured slump, 28-day compressive strength, static chord modulus, flexural response, and hydraulic conductivity; field observations were qualitative and noted slurry loss and surface boiling. The slump, from 50 to 220 mm, included 21 mixtures (84%) in the target range of 160–220 mm, while approximately 0.9 to 3.0 MPa, 0.63 to 1.05 GPa, and \:1.5\:×\:\:10⁻⁹ to \:1.3\:×\:\:10⁻⁸ m/s were the reported ranges for compressive strength, static chord modulus, and hydraulic conductivity, respectively. In the plotted results, only R19 and RK1 exceeded the specified compressive-strength threshold of 2.9 MPa; the latter was below the slump target. The hydraulic conductivities of the R- and QC-series were below \:1\:×\:\:10⁻⁸ m/s, while RA8-2 reached approximately \:1.3\:×\:\:10⁻⁸ m/s. Higher water–cement and bentonite–cement ratios in the tested mixtures were associated with lower stiffness, but the individual effects could not be isolated. These results support comparative mixture screening at 28 days, although the small-specimen tests and qualitative field observations do not establish wall-scale deformation compatibility.