Alternative laboratory technique to monitor the effect of cementing additives on clay for cut-off walls

Low permeability cut-off walls are regularly employed for groundwater and pollution control. In Europe, they are usually built out of cement-bentonite slurries. Generally, bentonite-cement slurries are studied in the laboratory to evaluate its strength, hydraulic conductivity and chemical compatibility. In this study, a nondestructive technique is proposed as an alternative method to monitor the hardening of clay treated with cementing additives. The technique makes use of bender elements to measure the shear wave velocity and the small-strain shear modulus (G0). Bender elements were installed in a flexible-wall hydraulic conductivity cell, so that G0 as well as the hydraulic conductivity of a single sample could be monitored versus time. Experimental work was carried out on cemented kaolin clay using Portland cement. Monitoring of G0 was shown to provide valuable additional information to study the stiffening of cemented clay