Ground treated by deep mixing methods has higher strength and lower compressibility than untreated ground. The hydraulic conductivity of the treated ground will be lower than that of the untreated ground for sandy and silty soils, but deep mixing treatment can increase hydraulic conductivity for clay soils. The strength of ground treated by deep mixing methods depends on such factors as the characteristics of the original ground, characteristics of the binder, amount of binder added, mixing energy, curing conditions, and loading conditions. Unconfined compressive strengths of treated ground range from about 30 to 400 psi for the dry method and from about 80 to 2,000 psi for the wet method. Typical contract specification values of unconfined compressive strength range from about 50 to 300 psi.
The Collin Group has utilized deep mixing columns to support a variety of structures from approach embankments for bridges to oil storage tanks.
Deep mixing refers to the blending of cement, lime, slag, and/or other binders in powder or slurry form to stabilize soil in-situ. When the binder is in powder form, the method is commonly referred to as the dry method. When the binder is in slurry form, the method is commonly referred to as the wet method. The choice of application method will depend upon the characteristics of a particular site and the desired performance characteristics of the treated soil. Mixing can be done with single-axis rotating tools to create single columns, multiple-axis rotating tools to create a set of overlapping columns in a single stroke, chainsaw-like mixing equipment to create continuous panels, mixing probes for mass stabilization, or other devices. For dry- and wet-method rotary mixing tools, binders are injected through the hollow stem of the rotating tool.
Dry-method rotary equipment is typically lighter than wet-method rotary equipment. Dry-method columns are typically about 2 to 3 ft in diameter, and wet-method columns can be up to about 8 ft in diameter. Depths of treatment are typically less than 60 ft for the dry method and 100 ft for the wet method, although greater depths are possible.