Construction Methods for Soil Cement Bentonite Slurry Walls

Soil Cement Bentonite, otherwise called S-C-B Slurry is a mix of the original soil backfill from a trench or hole with cement and bentonite slurry.  Most people are familiar with cement and soil, but bentonite slurry is a key part of the wall’s integrity. Bentonite slurry is made from bentonite clay, which can be found in Wyoming. The clay particles become very viscous when fully hydrated, which is key to creating an effective environmental sub-surface barrier.  The clay slurry takes between 30 minutes and 24 hours to become fully hydrated.

Steps For Wall Construction

First, a trench or hole must be created.  This must be deep enough to reach bedrock, or the water table depending on the purpose of the slurry wall and the nature of contaminates.  Then the floor of the trench needs to be cleaned up well enough that the slurry can have an effective seal.  Next the trench or hole will be filled or coated with bentonite and water slurry, which is only 2 to 4 percent bentonite by weight.  Then the trench or hole is refilled with a mix of bentonite slurry, cement, and soil: usually the soil that was removed from the area to create the trench or hole. These ingredients are mixed in batches and then poured or pushed down into the area that will become the wall.  Great care must be taken in the coating process and also in the mixing process.  If these are done carelessly, there could be windows in the wall, or areas that will let groundwater and pollutants through.

Advantages of Soil Cement Bentonite Slurry Walls

Most of the advantages of soil bentonite slurry walls apply, which include low cost, high productivity, and low permeability. Because the walls are constructed instead of naturally occurring, the continuity and depth are verifiable and there is no guesswork.  The main purpose is resistance to contaminated ground water while still being able to move with ground movements. Additionally, the slurry does remain fluid. One huge advantage is the low waste because of the re-use of materials.

Advantages that are unique to the soil bentonite mix containing cement include the superior strength. Trench stability is an important factor for slurry walls, and the S-C-B mix is fantastic because of the shorter backfill slope.

The S-C-B mixture also provides the best of both soil and cement slurry walls because it adds the impermeability of the soil bentonite with the resistance to erosion and deterioration that only cement can offer.  Animals cannot dig through walls with cement included in the mix.

Other Things to Consider With the Soil Cement Bentonite Mix

By adding the cement, the wall will be more permeable; at least in the beginning. Cement is particularly sensitive to acids and bases as well, so if the wall’s purpose is to protect from an acid contaminate a mix without cement may be preferable.

The purpose of the wall has to be considered strongly before making a decision on the exact mix for the wall.  Every aspect matters from climate to topography in addition to environmental factors. For overall satisfaction S-B-C slurry walls are a good option.