Soil Mixing
Soil Mixing provides a cost-effective solution for the rapid construction of retaining and cutoff walls by mixing soil in-situ with a cement or cement/bentonite grout.
Paddle or auger method
Historically soil mixing, which comprises the mixing of cement or lime into the in-situ soil, has been performed using single or multiple paddles at the toe of the kelly drill string or counter rotating continuous flight augers to form columns of treated ground or panels of interlocking columns. The mixing tools are generally mounted on a conventional piling mast.
The primary application of soil mixing is for the improvement of the engineering properties of the soil, in particular its shear strength, which leads to the improvement of the modulus and settlement characteristics of the composite soil and, in the treated portion of the soil, reduced permeability. Hence the most common application is predominantly in soft and weak soils, essentially water charged fine grained soils such as clay.
The cement or lime can be introduced and mixed into the soil in the form a water/cement grout, using a conventional slurry pump, when the process is described as wet mixing, or it can be introduced pneumatically as a powder, when it is described as dry mixing. The former method is more common but the latter, dry mixing method has particular application in very high water content soils, >50%, such as peats and other organic soils, where it avoids the introduction of more water into the soil and uses the in-situ water for hydration of the cement or lime.
Cutter soil mixing (CSM) method
Recent developments have introduced the CSM system of wet soil mixing, the installation equipment for which is derived from diaphragm wall cutter technology, in that it comprises two cutting and mixing drums, driven by compact hydraulic motors, as opposed to the simple paddle or auger equipment. The drums operate in counter rotation and are kelly mounted, on a conventional piling mast, providing a high degree of precision. This configuration is designed to combine high penetration rates with excellent soil/cement mixing.
The shape of the treated soil is rectangular and can therefore the soil mixing can be installed as individual units or continuous walls.
The CSM system incorporates the latest monitoring technologies and provides cost –effective solutions for the rapid construction of cut-off walls and retaining walls, the latter achieving their retaining function by the inclusion of steel “I” beams to satisfy the design integrity. Construction of walls using the CSM system follows the traditional primary and secondary sequence of panel installation, in which the secondary panels can cut back into the installed primary panels to yield excellent continuity in the finished wall.
A beneficial aspect of soil mixing is that minimal spoil is generated by either the wet or the dry method.
