Cement Bentonite Slurry Walls are a type of One Step Slurry Wall Construction

Cement Bentonite Slurry Walls self-harden and need no other backfill.

**CB Slurry Mix Plant**

Cement Bentonite (CB) slurry walls represent a smaller and more specialized portion of the slurry walls done in the US. In Europe and other overseas locations, CB slurry walls are more commonly used. With this method, the wall is excavated through a bentonite slurry that includes cement. The trench slurry hardens overnight without a separate backfilling operation and this technique is sometimes referred to as one-step slurry wall construction. The first use of a CB slurry wall in the US dates back to the early 1970s.

Advantages of Cement Bentonite Slurry Walls

No separate backfilling operation, so the work can be done in conditions of relatively narrow or restricted access.
If the subsurface soils are unsuitable for use in backfill, it is not a problem, since all of the backfill is manufactured CB slurry.
Since CB slurry is heavier than bentonite slurry and self-hardens, this method can provide improved trench stability and more easily overcome weaker ground conditions.
Since the slurry sets after about a day, segments can be constructed in any direction, in any order, and simply joined together to make a continuous barrier.
Since the slurry sets, segments can be used to traverse up or down a sloped ground surface with minimal earthwork construction.
The CB slurry will permanently fill any voids and fractures encountered to allow construction through very porous ground conditions.
CB slurry trenches are often advantageous on smaller projects where a small CB mix plant and excavator can often solve seemingly difficult conditions at an attractive price.
CB can provide a liquid but self hardening fill to allow the excavation and removal of unsuitable materials below the groundwater without shoring or dewatering.
The CB slurry, once set, has more strength than SB backfill.

Slurry Wall Equipment Working in tight access conditions

Construction Method for Cement-Bentonite Slurry Walls

CB walls may be excavated using hydraulic excavators and/or slurry clamshell equipment, the same as other slurry walls. At the slurry plant, cement, or some other setting agent is added to the bentonite slurry. The viscosity of the mixed slurry is designed to be in the fluid range during the excavation process. The slurry is then pumped through temporary tubing from the mix plant to the excavation. Once the excavation is to full depth, the bottom is cleaned and the process moves on. The slurry stays in the trench and is allowed to set. Typical CB slurry will attain a butter-like consistency overnight and a clay-like consistency after fully hardening in about 90 days. A picture of our large CB slurry mix plant on a recent project is shown below.

**CB Slurry Hardens Overnight**

Properties of Cement Bentonite Slurry Backfill

Typically, the properties of interest for CB slurry walls are strength and permeability. Because a typical CB slurry has a relatively high water content, there are a more water-filled voids than with a Soil Bentonite backfill. This means that typical permeability values are higher, in the range of 10-6 cm/sec. Typical short term values of permeability for a standard Portland cement CB mix are shown in the plot below from a recent project. Since CB takes months to fully harden, long term tests have shown CB permeability will gradually decrease (improve) However, permeability is sometimes not the only parameter of interest in containing groundwater. CB has a pore size that is particularly well-suited to resisting certain oils and petroleum products and thus it is often preferred on these projects.

**Short Term CB Permeability**

**Short Term CB Strength**

It is also possible to create a CB backfill using special cements and other additives for lower permeability and improved strength. With these more costly materials, permeability values in the range of 10-8 cm/sec and strengths in excess of 80 psi (0.5 MPa) are possible after 90 days of curing. A design mix program usually recommended to optimize CB performance.

Learn More about Slurry Cut-Off Walls

Geo-Solutions has authored and participated in over 50 different papers on slurry walls. View our library to read and download several slurry cut-off wall technical papers.
Learn more from case studies on slurry walls in our Section on Case Studies.
Learn more and view pictures of our slurry wall equipment in our Section on Equipment.

Slurry Wall Sample Specifications

Read and download Geo-Solutions sample specs for soil bentonite slurry cut-off walls, cement bentonite slurry walls, soil-cement-bentonite slurry walls, composite slurry walls, bio-polymer slurry groundwater collector trenches.

Call Us Today

For help with slurry cut-off walls utilizing various types of bentonite slurry mixes, call us at 724-335-7273.