Foundation, Concrete and Earthquake Engineering

Liquefaction Mitigation by Deep Soil Mixing Method (DSM)

Deep soil mixing (DSM) is an effective and versatile method of preventing damage caused by soil liquefaction. Liquefaction is the weakening and subsequent instability of soils caused by applications of force such as seismic activity, erosion, construction, or excessive load bearing. Significant movement shifts the underlying soils, allowing groundwater to rise and fill the spaces created by the movement. This release of water weakens the composition of otherwise stable soil. Soil can also become saturated and unstable through industrial dumping or by leakage from faulty retaining structures.

Too Much Moisture Creates Big Problems

When the soil contains too much water, it can fail to provide support for building foundations, causing them to shift, crack or even collapse. It can also render some geographical areas unsuitable for building by creating soil that is too wet and soft to allow safe construction. Not only is the soil too unstable to support the significant weight of new building construction, it can render existing buildings unsafe. Failure to contain liquid soils can result in seepage of toxic or noxious substances (chemicals, sewage or other waste products).

Deep Soil Mixing Can Solve Liquefaction Issues

An effective way to conduct Soil liquefaction mitigation is through seep soil mixing (DSM). The DSM method involves boring through the soil with a specialized, large-diameter auger (between three and 12 feet) equipped with mixing paddles. Once the auger reaches the appropriate depth, it is filled with cement that is released through holes on the core of the auger. As the cement fills the hole, the mixing paddles combine it with the surrounding soil to create a solidified, underground column.

In addition to its uses in building construction, DSM is also utilized in projects that require sludge stabilization such as Brownfield redevelopment and industrial cleanup. In these cases, DSM technicians can use soil reagents such as fly ash or harder, less porous soil types to reduce the moisture level of the sludge.

DSM can also be used for chemical remediation. By solidifying contaminated soil with either cement or other binders, the contaminants in the soil are isolated and solidified, preventing them from seeping into nearby water supplies. New developments include the use of zero-valent iron, carbon and special clays to create solid soils and reduce the impact of liquefaction. Traditional cement columns and solidifying agents are both effective methods of barrier construction to protect environmentally sensitive areas from infiltration, or to stabilize areas prone to soil erosion

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