Dry soil mixing is a ground improvement technique that improves very soft clays, peats, organics, and other weak soils by mechanically mixing them with a dry cementitious binder to create a stabilized soil-cement element, typically referred to as soilcrete.
Process
The dry mixing process uses high-speed drilling equipment to advance a drill rod with a mixing tool consisting of radial mixing paddles into the ground.
During penetration, the tool shears through the soil to the required depth. After the tool reaches the design depth, the dry binder powder is pneumatically pumped through the drill stem and exits just above the tool, where it is blended with the previously sheared soil as the tool is withdrawn.
The dry soil mixing process constructs a circular soilcrete column that can be designed as individual elements, rows of overlapping columns (referred to as panels), or as 100% mass stabilization, all with a specified unconfined compressive strength. It is low-vibration, quiet, clean, and uses readily available materials.
This process is often used in high groundwater conditions and creates almost no spoil for disposal. Treatment is possible to depths up to 60 ft. Obstructions are sometimes pre-drilled ahead of column construction.
Ideal dry soil mixing ground conditions
Soils vary widely in their ability to be mixed, depending on factors such as soil type, strength, water content, plasticity, stratigraphy, and texture.
Dry soil mixing is best for very soft and weak soils (clays, peats, organics) with moisture contents at or above the liquid limit (typically well above 60% moisture content).
Related geotechnical techniques
Select a technique:
Common uses
- Improve shear capacity and increase slope/global stability
- Reduce lateral loads for earth retention structures
- Increase bearing capacity, providing structural and foundation support
- Decrease compressibility and settlement
- Mitigate liquefaction and seismic issues
- Stabilize contaminants in place
Advantages
- Quiet and vibration-free
- Environmentally friendly, using readily available materials with almost no spoil
- Can be used to solve numerous geotechnical and groundwater issues
- Can be used individually or combined with other solutions to reduce costs
- Can reduce construction time versus conventional methods.
- Elements can be installed to form various efficient geometries
Quality assurance
Pre-production laboratory testing is used to evaluate the required binder type and volume and to help establish installation methodology. Mixing shaft speed, extraction rate, batching, and pumping operations are typically adjusted after constructing one or more test columns on site.
Data acquisition systems are used on all mixing rigs for real-time monitoring of mixing parameters throughout the mixing process. Coring of cured columns can be used to verify the unconfined compressive strength. A camera can be lowered into a core hole for visual inspection. Test columns can be excavated for visual inspection of the soilcrete. In situ testing options for the elements are also available.
Related projects
Power
Los Vientos Wind Farm
Keller’s production rate was 33% faster than anticipated, effectively shaving six weeks off the ground improvement project schedule.
Infrastructure
Marco Island Executive Airport
Keller provided a design-build ground improvement solution to support the construction of the new airport.
Tanks
Port Everglades Fuel Storage Tanks
Marshy subsurface conditions required ground improvement for the construction of eleven new fuel storage tanks.
Infrastructure
Missouri River Wastewater Treatment Plant
Dry soil mixing was used at the Missouri River Wastewater Treatment Plant to stabilize soft soils to protect against riverbank failure.
