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Wet Soil Mixing

Wet soil mixing, also known as the Deep Mixing Method, is a ground improvement technique that improves the characteristics of weak soils by mechanically mixing them with cementitious binder slurry. To construct columns, a powerful drill advances drill steel with radial mixing paddles located near the bottom of the drill string. The binder slurry is pumped through the drill steel to the tool as it advances and additional soil mixing is achieved as the tool is withdrawn. To perform mass wet soil mixing, or mass stabilization, a horizontal axis rotary mixing tool is located at the end of a track hoe arm.

The binder slurry is injected through a feed pipe attached to the arm. The process constructs individual soilcrete columns, rows of overlapping columns or 100% mass stabilization, all with a designed strength and stiffness. The technique has been used to increase bearing capacity, decrease settlement, increase global stability, and mitigate liquefaction potential for planned structures, tanks, embankments and levees. Wet soil mixing has also been used to construct in situ gravity retaining structures, and to facilitate tunnel construction or remediate the impact tunneling may have on nearby structures. Soil stabilization by wet soil mixing can provide structural support and/or it can greatly reduce lateral loads on bulkhead walls.

Wet soil mixing is best suited for soils with moisture contents up to 60 percent. Soft cohesive soils are usually targeted as other soil types can often be treated more economically with other techniques.  If the moisture content is greater than 60 percent, dry soil mixing may be more economical. Soils vary widely in their ability to be mixed, depending on the soil type, strength, water content, plasticity, stratigraphy, and texture. Almost any soil type, including organics, can be treated with wet soil mixing although some soils may require significant binder and/or pretreatment. With wet soil mixing, treatment is possible to depths up to 100 feet. Depending on the soil type, excess soilcrete generated may range from 10 to 40 percent of the treated volume. Stiff soils and obstructions are sometimes predrilled ahead of the soil mixing process.

Mixing shaft speed, penetration rate, batching, and pumping operations are typically adjusted after constructing one or more test columns in a convenient area on site. Pre-production laboratory testing is used to prescribe mix methodology, energy, and the grout slurry system. Hayward Baker has developed proprietary special equipment and software for the real-time monitoring of all mixing parameters during the wet soil mixing process. Wet sampling in fresh columns and coring of cured columns can be used to verify strength. Test columns can be excavated for visual inspection of the soilcrete. Visual inspection is possible with a camera lowered into a corehole.

Contact your local Hayward Baker office for more information.

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