Description of Work:
A cement-bentonite slurry wall was constructed at the Winyah Generating Station located in Georgetown, South Carolina. The completed slurry wall was 6,998.5 square feet and was excavated to backhoe refusal between 45 and 47 feet below ground surface. The purpose of the slurry wall was to stop an area of seepage along a containment dyke surrounding one of the electrical plant’s slurry ponds.
The cement-bentonite slurry was mixed using two separate 5 CY lightning mixers. The bentonite slurry was mixed at a ratio of 0.055 bentonite-water. After complete mix and hydration, the bentonite slurry was transferred to the second mixer. The cement was mixed at a ratio of 0.30 cement-water and was added using pre-weighed jumbo sacks. Type V Portland (sulfate resistant) cement was used due to the nature of the specific groundwater contaminants.
One sample of cement-bentonite slurry was collected per each day of and was tested in accordance to ASTM 5084 (Hydraulic Conductivity) and ASTM 1633 (Unconfined Compressive Strength). The project specifications required a minimum hydraulic conductivity of 1.0 x 10-6 cm/sec and a minimum unconfined compressive strength of 20 psi.
Unconfined compressive strengths ranged from 31 psi to 224 psi and hydraulic conductivity values ranged from 9.2 x 10-7 to 3.3 x 10-7 cm/sec. All offsite laboratory testing was performed by GAI Consultants, Inc.