A slurry trench is a nonstructural underground wall that serves as a barrier to the horizontal flow of water and other fluids. It is constructed with the aid of a viscous stabilizing fluid known as slurry (Fig. 1). The two most common types of slurry trenches are referred to as soil-bentonite (S-B) and cement-bentonite (C-B). In the S-B method, a bentonite-water slurry is introduced into the trench during excavation to provide side wall support. After the trench is excavated to its required depth, a mixture of soil, bentonite, and water is placed into the trench displacing the bentonite-water slurry. Generally the excavated soil is used in the backfilling operation; however, if it contains an excessive amount of contaminated or undesirable material such as cobbles or clay lumps, a selected backfill material may be required.
In the C-B method, cement is added to the bentonite-water slurry just prior to its introduction into the trench. In addition to serving as a stabilizing fluid to maintain an open trench during excavation, the cement-bentonite slurry remains to set up and form the permanent cutoff wall. Although in most cases either method can be used, a C-B slurry trench offers many advantages over the S-B method as indicated in Table 1.