The technique was created in the 1970s and 1980s in Japan and Scandinavia, initially to improve the bearing capacity of very soft clay soils. Bachy was a trailblazer in this field, introducing its Colmix® process into Western Europe as early as 1986. Since then, the Deep Soil Mixing technique has been extended to a wide range of soil types and applications.

In practice, this technique consists of mechanically mixing the in-situ soil while incorporating a cementitious material, which is usually made of one or several hydraulic binders such as cement, blast furnace slag, lime, fly ash, etc.

This technique encompasses several different processes:

• The Colmix® process, which enables the formation of columns using one or more vertical rotating tools with mixing blades and mounted on piling rigs
• The Geomix® process, which creates wall panels using a CSM (Cutter Soil Mixing) tool based on technology derived from the Hydrofraise® process
• The Trenchmix® process for constructing continuous walls using a trencher
• The Springsol® process uses a small-diameter auger to form small-diameter vertical, inclined or sub-horizontal columns. This process is particularly suitable for use in confined spaces or where working height is limited.

Deep Soil Mixing has many applications across a broad spectrum of construction projects, including:

• The improvement of compressible soils subject to distributed loads: industrial warehouses, storage areas and linear structures such as rail and motorway embankments
• The treatment of soils to mitigate the risk of liquefaction
• The construction of continuous cut-off walls on levees and dikes, or low-permeability enclosures to contain polluted areas
• The construction of temporary or permanent retaining structures in combination with vertical strengthening elements (steel beams, pipes and/or pre-cast piles)
• Consolidation of embankment/cut slopes using transverse shear walls

Generally speaking, this technique is appropriate for any soil type. The soil/binder mix is a semi-rigid material behaving halfway between natural soil and concrete, and offers improved mechanical and hydraulic properties compared to the original soil.

What are the benefits of this technique?

Implementation

All these processes usually involve three stages: mechanical destructuring of the existing soil, incorporation of the mix and homogenisation of the mixture. Very often, all three stages are carried out simultaneously.

The binder mixed with the soil is selected and designed to obtain the hydraulic and/or mechanical characteristics required by the project. Where the technique is used to remediate polluted ground, the binder can be chosen specially to neutralise the pollution.

Once combined, the soil-cement mixture forms either columns, wall panels or continuous trenches.

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