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  • Writer's pictureSi Shen

Engineering properties of Peat

Peat is generally considered as highly problematic and one of the least wanted soil types you want your foundation to be in. It is an organic soil, which means the soil skeleton is made up of fibres of dead plants and animals rather than minerals. Peat can exist in marshland areas and exist in layers in Alluvium.

From a geotechnical engineering perspective, peat usually brings these hazards:

  • High compressibility and creep, resulting in large settlement. A peat stratum can reduce in thickness by more than 50% under a relatively modest increase in effective stress of the order of 50 kPa.

  • High moisture content. It can have large cavities that contain free water. Water content by volume is typically 75% to 98%.

  • Low bulk density.

  • Low undrained shear strength. Undrained shear strength can be in the order of 5kPa.

  • Potential gas content. Gas may be trapped in peat due to decomposition of dead organic materials and may contain methane, which is flammable and therefore a fire hazard.

Mitigations to the undesirable characteristics of peat:

  • Pre-loading with surcharge. This helps peat to squeeze out water (consolidate). A load that is equivalent to or slightly higher than the long term design load is applied to the surface and the settlement of the peat is monitored. Load is removed and construction started once the settlement reaches certain pre-defined value.

  • Installing drainage system. This help peat to consolidate and settle.

  • Ground improvement, including dig-and-replace, jet grouting, deep soil mixing and soil reinforcement

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