IMPACT OF MOLDING WATER-CONTENT ON HYDRAULIC CONDUCTIVITY OF COMPACTED SAND BENTONITE

The relationship between molding water content and hydraulic conductivity of a compacted sand-bentonite mixture was examined in a laboratory test program. This program involved triaxial permeability testing of nine specimens of 80% bentonite and Ottawa sand, compacted at standard Proctor density using molding water contents ranging from 6 to 19%. The permeability tests were conducted using hydraulic gradients ranging from 19 to 40. The specimens were subjected to an average effective stress during testing of 21 kPa. The tests were conducted using continuous back pressure saturation. Each test was run for a minimum of 40 000 min (approximately 28 days) to enable the flow in and out of the specimen to come to equilibrium with respect to each other. The hydraulic conductivity decreased from 6.5 x 10(-9) cm/s for a molding water content of 5.90% to 1.4 x 10(-9) cm/s for a molding water content of 15.8%. However, although the hydraulic conductivity was related to the molding water content, the variation in hydraulic conductivity was relatively small. Therefore, the low values reported for all hydraulic conductivity tests suggest that molding water content is not a critical design factor in the construction of a low-permeability sand-bentonite liner.