Wet soil mixing (WSM), also known as the deep soil method (DSM) or deep mixing method (DMM), improves the properties of weak, compressible soils by mechanically blending them in situ with a designed cementitious binder slurry to create stabilized soil-cement columns, typically referred to as soilcrete.
Process
A powerful drill advances a mixing tool into the subsurface soils as the designed grout slurry is pumped through ports along the bottom cutting paddles. The soils are mixed in a top-down approach to the target depth. Additional mixing energy and binder can also be added as the tool is withdrawn to the surface.
This process constructs individual circular soilcrete columns, which can be designed as individual elements, rows of overlapping columns (referred to as panels), or as 100% mass stabilization, all with a designed unconfined compressive strength and/or permeability. It is low-vibration, quiet, and uses readily available materials.
Wet soil mixing is a volumetric process that creates stabilized excess materials that can be beneficially reused onsite as structural fill.
Treatment is possible to depths up to 120 ft, although depths of up to 70 ft are typical. Obstructions are sometimes pre-drilled ahead of column construction.
Ideal wet soil mixing ground conditions
Wet soil mixing applies to most cohesive and granular soils with low bearing capacity and high compressibility; however, ease of mixing depends on soil type, strength, density, water content, plasticity, stratigraphy, and texture.
Wet soil mixing is also suitable for organic soils, contaminated soils, and high groundwater conditions. Note that for soils with moisture contents at or above the liquid limit (or typically well above 60% moisture content), dry mixing may be more applicable.
3D animation
Related geotechnical techniques
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Common uses
- Increase bearing capacity for structural and foundation support
- Decrease compressibility and settlement
- Mitigate liquefaction and reduce dynamic settlement
- Improve shear capacity and increase slope / global stability
- Temporary shoring for deep excavations
- Reduce lateral loads for earth retention structures
- Reduce permeability for groundwater control
- Cut-off walls to mitigate seepage or contaminant transport
Advantages
- Quiet and vibration free
- Excess material can be limited and/or reused onsite to limit transporting spoils
- Uses readily available materials
- Can be used individually or combined with other solutions to reduce costs
- Can reduce construction time versus conventional methods
- Can be used to solve numerous geotechnical and groundwater issues
- Elements can be installed to form various efficient geometries
Quality assurance
Pre-production laboratory testing is used to evaluate the required grout mix design and validate the installation methodology. An on-site test program is often conducted to validate grout mix and installation parameters (grout volume, mixing energy, penetration rate), as well as batching and pumping operations.
Data acquisition systems are used on all mixing rigs to monitor mixing parameters in real time during the mixing process. Test columns can be excavated for visual inspection of the soilcrete. Wet sampling in fresh elements and coring of cured elements can be used to verify strength and permeability. Visual inspection of the in situ soilcrete elements is possible with a camera lowered into a core hole. In situ testing options for the elements are also available.
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