Deep Soil Mixing

Deep Soil Mixing (DSM) is a soil treatment whereby the soil is blended with cementitious and/or other reagent materials. The reagent is injected through the hollow rotating kelly bars, with some type of cutting tool at the bottom. The Kelly bar above the tool may have additional discontinuous auger flights and/or mixing paddles or blades.

1) Conventional Deep Soil Mixing (DSM)

• Deep Soil Mixing is a soil improvement technology used to treat soils in situ to improve strength and reduce compressibility. The process involves deep soil mixing of grout or binder with the soil to create cemented or improved soil. The wet method is where the binder is introduced in flurry form, as opposed to the dry method where the binder introduced with air. With wet mixing, the most commonly used binder is cement.

2) In-Situ Solidification/Stabilization

• In-Situ solidification/stabilization of contaminated soils can be achieved using Cement Deep Soil Mixing (CDSM) technology. In deep soil mixing, powerful augers are used to mix slurry of possolanic additives into a soil or sediment in-situ, thereby stabilizing it for construction purposes.

Basic DSM Treatment Patterns

DSM’s are a soil treatment whereby the soil is blended with cementitious and/or other reagent materials to treat soils in situ to improve strength and reduce compressibility. DSM Columns are normally installed in soft soils where settlement must be reduced and stability increased. DSM Deep soil mixing applications have also been used to treat contaminated soil, sediment, and sludge at remediation projects. Soil mixing has been used to treat soil, sediment, and sludge. The technology is proven effective for treatment of both inorganic and organic hazardous constituents. Selection of the appropriate technique depends on several factors, including the type of geotechnical constraint, the characteristics of the soil, and the desired end result. While most commonly used in cohesive soils, they also have application in loose to medium dense sands where the low-cost cementation they provide can avoid liquefaction. Full-scale S/S and DSM projects have treated inorganic constituents including lead, cadmium, arsenic and chromium and organic constituents including coal tars, refinery wastes, creosote, other polycyclic aromatic hydrocarbons and polychlorinated biphenyls (PCBs).

Binding reagent(s) can be mixed into subject material after the material has been excavated or while the material remains in place (in-situ treatment). Mobile equipment such as a pugmill can be brought to a remediation site to mix binding reagents into excavated material. For in-situ mixing, equipment such as backhoes, soil mixing augers, in-situ blenders, and road reclaimers are used.

Soil Mixing Applicants include:

• Construction of cut-off walls for control of groundwater and contaminants,
• Increasing bearing capacity of sub-grade for structures,
• Encapsulation of pollutants / chemicals treatment of contaminants,
• Controlling heave in soft clays, on excavations bottoms,
• Excavation support / installation of temporary or permanent retaining walls,
• Area loads and point load structural support,
• Seismic induced settlement / lateral spreading and mitigation of liquefaction potential

• Effective method for settlement control, liquefaction, mitigation and remediation of contaminated soils.
• Reduced vibration – Method induces very low vibrations, which reduces the potential impact to nearby utilities.
• Reduces off-site disposal problems.
• Time saver – process is quick, and deeded strength is achieved in difficult soil conditions.
• Ability to construct large diameter soil columns, in a cleaner environment.

• Factors that may limit the applicability and effectiveness of the in situ S/S include:
• Depth of contaminants may limit some types of application processes.
• Future usage of the site may 'weather' the materials and affect ability to maintain immobilization of contaminants.
• Some processes result in a significant increase in volume (up to double the original volume).
• Certain wastes are incompatible with variations of this process. Treatability studies are generally required.
• Reagent delivery and effective mixing are more difficult than for ex situ applications.
• Like all in situ treatments, confirmatory sampling can be more difficult than for ex situ treatments.
• The solidified material may hinder future site use.
• Processing of contamination below the water table may require dewatering.

The DSM methods and technologies costs vary considerably with configurations, reagents, water tables, depths, soil characteristics and access. . We suggest you using RECON’s FREE budgetary estimating service though www.deepsoilmixing.com to get an order of magnitude figure.

DSM provides a safe method of construction and omits the need for deep excavations; temporary works to adjacent buildings, export of contaminated fill, working below the water table and does not require importing of fill material. DSM provides an economical, reliable way of satisfying a difficult set of technical perimeters and meeting project schedules. The construction process for the installation of the soil mix column is not affected by the weather which can be a significant advantage over other construction methods.