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Dry Soil Mixing

Dry soil mixing is a ground improvement technique that improves the characteristics of soft, high moisture content clays, peats, and other weak soils, by mechanically mixing them with dry cementitious binder to create soilcrete. To construct columns, a high speed drill advances drill steel with radial mixing paddles located near the bottom of the drill string. During penetration, the tool shears the soils preparing them for mixing. After the tool reaches the design depth, the binder is pumped pneumatically through the drill steel to the tool where it is mixed with the soil as the tool is withdrawn. To perform mass soil mixing while implementing mass soil stabilization methods, a horizontal axis rotary mixing tool is located at the end of a track hoe arm. The binder is pneumatically injected to the soil mixing tool through a feed pipe which is attached to the track hoe arm.

The dry soil mixing 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, mitigate liquefaction, fixate contaminants in situ, decrease settlement and increase global stability for planned structures, embankments and levees. Dry soil mixing is low vibration, quiet, and clean, and uses readily available materials. The process is often used in high ground water conditions and has the advantage of producing practically no spoil for disposal.

Dry soil mixing is best suited for soils with moisture contents greater than 60 percent and near the liquid limit. Soft cohesive soils, including organics, are usually targeted as other soil types can often be treated more economically with other techniques. Soils vary widely in their ability to be mixed, depending on the soil type, strength, water content, plasticity, stratigraphy, and texture. Organic soil and peats can often offer a good degree of stabilization, but laboratory testing is always recommended prior to design. With dry soil mixing, treatment is possible to depths up to 60 feet. Obstructions are sometimes predrilled ahead of the soil mixing process.

Pre-production laboratory testing is used to prescribe mix methodology, energy, and binder content. Mixing shaft speed, extraction rate, batching, and pumping operations are typically adjusted after constructing one or more test columns on site. Hayward Baker has developed proprietary special equipment and software for the real-time monitoring of all mixing parameters during the dry soil mixing process. Coring of cured columns can be used to verify strength. Excavation can be performed on test columns 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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