Slurry wall

Abstract: Soil-bentonite cutoff walls constructed by slurry trench methods have been employed for about 3 decades. Soil-bentonite cutoff walls are constructed by excavating a continuous narrow trench under a bentonite slurry that stabilizes the excavation. The trench is backfilled subsequently with a blend of natural soil and bentonite, thereby displacing the slurry. The completed wall acts as a barrier to lateral flow of water and most fluid pollutants. Presented are the results of various investigations made to determine the design factors relating to permeability, compressibility, and strength properties of cutoff walls. These properties are related to the composition of the backfill materials and construction methods. Data are presented on the ability of slurry trench cutoff walls to maintain their integrity under the effect of long-term permeation by various pollutants. Recommendations are made for writing specifications that will achieve required performance at the lowest cost.

Abstract: In both the United States and the United Kingdom, slurry walls are used as vertical barriers to control groundwater flow and to contain contaminants as part of waste containment systems. In the United States, slurry walls are commonly constructed using soil-bentonite ~SB! and the barrier typically consists of a mixture of select soil, bentonite, and bentonite-water slurry. Alternatively, in the United Kingdom, the barrier wall comprises a mixture of cement, blast furnace slag, and bentonite-water slurry. After a comparison of the two techniques, this paper presents the results of permeability and unconfined compressive strength tests on twenty-one different mixtures of slag-cement-bentonite ~slag-CB!. The slurry wall materials tested in this study were prepared using sample formulations originating in the United Kingdom and materials originating in the United States. Unconfined compression tests were performed on samples after one month of curing, while permeability tests were performed after one, two, three, six, and twelve months of curing. For the mixtures tested and cured twelve months, two mixtures ~one having 20% cementitious material with 70% slag replacement and another having 15% cementitious material with 80% slag replacement! were found to have the lowest hydraulic conductivity s2 3 10 ˛8 cm/ sd. The data show that 0 to 60% slag replacement had little effect on hydraulic conductivity of the resulting slag-CB mixtures. However, the hydraulic conductivity drastically decreases as the slag replacement increases from 70 to 80%. As expected, the unconfined compressive strength increased as the cementitious material content increased from 10 to 15 to 20%. The slag-CB consolidates rapidly and has compression characteristics similar to other high moisture materials.

Abstract: Synopsis Hydrostatic pressure, arching of the soil and electro-osmotic forces have each been suggested as the dominant factor to account for stability of trench excavations in cohesionless soils supported by clay slurries. The Authors suggest that the most important mechanism is the hydrostatic pressure of the slurry. However, the increase in density of the slurry due to the suspension of cuttings must be considered in computing this hydrostatic pressure. While a concrete diaphragm cut-off was under construction at Pierre-Benite, France, an unexpected flood occurred, causing several slips in the trench excavation. The analysis of these slips is presented and it confirms that the stability of a slurry trench in cohesionless soil can be accounted for provided that the correct density is used in computing the hydrostatic pressure of the slurry. La pression hydrostatique, l'effet d'art du sol et les forces electro-osmotiques ont tous ete suggereś comme facteur dominant pour estimer la stabilite des excavation...