Composite and Combination Slurry Walls Can Solve Complicated Groundwater Problems

Using Plastic Sheeting, and other methods, A Composite or Combination Slurry Wall groundwater Barrier can be customized for a specific problem.

**Steel Piles Installed in Slurry Wall**

Composite Slurry walls are typically made by adding another material, such as a plastic sheet, into a soil-bentonite or cement-bentonite slurry wall to improve the overall properties of the barrier. The added material could be a plastic sheet designed to improve the water or gas permeability, or a steel member designed to improve the shear strength or structural properties of the composite wall.

Combination slurry wall systems feature a combination of different slurry wall techniques. For example; a soil-bentonite slurry wall could incorporate CB panels to better traverse a steep slope or jet grouted panels to safely encase buried utility pipes. When bio-polymer trench drains are included, the combination slurry wall system can both stop groundwater and permit extraction of the groundwater. There can be many kinds of composite slurry walls and combination slurry wall systems. More information on combination slurry wall systems is available in our sections on bio-polymer trench drains and permeable reactive barriers.

Advantages of Composite Slurry Walls

Use of the slurry method allows for the economical insertion of vertical panels or elements into the ground in a narrow self-supporting trench, even below the groundwater table.
Use of plastic panels may be necessary in extremely aggressive groundwater environments or in cases where methane or other gas migration is to be prevented.
The use of the slurry trench techniques provides a way to install steel sheeting in difficult driving conditions.

Advantages of Combination Slurry Wall Systems

Minimum cost for maximum benefit using two or more slurry wall technologies.
Capability to solve isolated constructibility issues with minimum cost and risk.
Capability to modify groundwater patterns by diverting, extracting or containing groundwater with one continuous system.

Construction Methods for Composite Slurry Walls

Generally, the slurry wall methods used to excavate the slurry trench are the same as any of the other methods described elsewhere. The plastic panels can be inserted by a variety of methods depending on the type of sheet and type of joint selected. The pictures below show plastic panels being inserted into excavated slurry supported trench.

**Inserting plastic sheet with overlapping joints into slurry trench.**

The first picture shows plastic sheets being inserted with overlapped joints into a slurry trench. A wide overlap, slurry, and pressure from the backfill seal the joint. The second picture shows plastic sheets being inserted with interlocking joints into a slurry wall. The interlock joints can be held together with a sealant for a more positive seal. A temporary steel frame suspended by a crane is used to hold the sheets in place while the interlock is made.

**Inserting plastic sheet with interlocking joints into slurry trench.**

Properties of Composite Slurry Walls

Generally, composite barrier walls have permeability values that are too low and too complex to measure. On a recent project in Australia, a composite slurry wall with a plastic sheet and overlapping joints sustained a vacuum for a period of over a year, indicating a very tight system. On another project in Arizona a composite slurry wall with a plastic sheet and interlocking joints has performed well without measurable leakage for over 10 years. While composite slurry walls are more costly and more difficult to install, they provide an additional safety factor in performance.

Combination Slurry Wall Systems

Combination slurry walls are most often designed to address the particular needs of a specific project, but some combinations occur repeatedly in similar applications. Perhaps the most common combination is the soil-bentonite slurry wall installed in parallel with a bio-polymer trench drain. This combination is often employed around landfills or other contained waste facilities that need to dewater inside the facility without removing and treating large volumes of groundwater from outside the same facility. A cross section of a typical combination slurry wall system is shown in the schematic.

**Typical Combination Slurry Wall System**

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.