Abstract
Deep Soil Mix (DSM) is a proven method of ground improvement for deeper underlying soft soil layers which are otherwise impractical to reach using conventional shallow soil stabilization and replacement methods. The predominant binder materials used are Ordinary Portland cement (OPC) and Lime (CaO) but negative effects to the environment from manufacture and increasing construction cost have prompted research into alternative materials. This review identifies pozzolans and filler materials as possible supplements or partial substitutes for better results. The DSM method and binder reaction processes during treated soil strength development are outlined and effectiveness of different pozzolans (Fly Ash, Silica Fume, Ground Granulated Blast Furnace Slag, Rice Husk Ash, Kaolin, and Metakaolin) and filler materials (e.g. fine sand) discussed together with their influence factors. With many pozzolans, a clear optimum dosage is observed where improved strength peaks. Aluminosilicate pozzolans perform better over siliceous pozzolans with Metakaolin (MK) identified as the most effective pozzolan for enhancing compressive strength. Up to date research results on these materials are compiled. MK blended cements are readily available and can be readily applied for initial field tests. Treated soil strength may be regulated with addition of filler materials to further reduce reliance on cement.
Highlights
Construction in soft soil conditions require either wide footprint or deep foundations to support the overlying structure without soil shear failure or excessive settlement
Adding pozzolan materials to lime / cement binder mix can be effective when treating soils with little or no pozzolanic particles since follow on strength development beyond short term hydration is due to pozzolanic reactions [37]
The following conclusions are made: Cement is well established as the binder of choice in Deep Soil Mix (DSM) ground improvement
Summary
Construction in soft soil conditions require either wide footprint or deep foundations to support the overlying structure without soil shear failure or excessive settlement. The Deep Soil Mix (DSM) method applies soil stabilization principles, which comprises the addition and mixing of binder materials with the soil as stabilizing agents and other filler materials in the form of columns into the soil stratum. In DSM, specialized equipment auger to depth, and inject binder material / filler material which reacts with the existing soil to form columns of improved soil. DSM has been applied in soft ground conditions such as marine clay, alluvial deposits, organic soils and peat. For a wet mixing method, the binding agent is turned into wet slurry form and pressure injected into the soil through nozzles located at the end of a specialized soil auger. For the dry mixing method (considered more economical than WDSM), the dry binder is injected (using compressed air) into the soil at depth and thoroughly mixed with moist soil. DDSM is more appropriate for soft soils with high moisture content, organic soils and sludges [3]
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