Embankments constructed on soft soils have a tendency to spread laterally because of horizontal earth pressures acting within the embankment. These earth pressures cause horizontal shear stresses at the base of the embankment that must be resisted by the foundation soil.  If the foundation soil does not have adequate shear strength, failure can result. Properly designed horizontal layers of high strength geotextiles or geogrids can provide reinforcement, which increase stability and prevent such failures. Both geogrids and geotextiles can be used equally well provided they have the requisite design properties. There are some differences in how they are installed, especially where there is no root mat or vegetative layer, geogrids may require a lightweight geotextile separator to provide filtration and prevent contamination of the first lift if it is sand, which meets soil filtration criteria.

The reinforcement may also reduce horizontal and vertical displacements of the underlying soil and thus reduce differential settlement. It should be noted that the reinforcement will not reduce the magnitude of long-term consolidation or secondary settlement of the embankment.

The use of reinforcement in embankment construction may allow for:

  1. an increase in the design factor of safety
  2. an increase in the height of the embankment
  3. a reduction in embankment displacements during construction, thus reducing fill requirements
  4. an improvement in embankment performance due to increased uniformity of post-construction settlement, and
  5. shorten the time required to complete construction.

The Collin Group has been design engineer of record for numerous embankments over soft ground.

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