The decision to use an overlap or seam is based on the following:

  • Weakness of the sub grade upon which the geosynthetic is directly placed with respect to the potential for mud waving during the backfill operation
  • Material and labor costs of deploying individual geosynthetic panels with extra material required for the overlap versus the material and labor costs of seaming and installing large, fabricated panels
  • Feasibility of deploying individual geosynthetic panels in poor access and/or climatic conditions
  • Required seam strength being achievable

The table below is provided as a guide for determining overlap requirements for separation/stabilization applications based on sub grade strength and suggest that when the sub grade soils upon which the geotextile is directly placed provides a shear strength less than CBR = 0.5, the designer should require adjacent geotextile panels to be seamed.

A simple cost analysis generally indicates sewing to be economical when overlaps of 3.3 feet or greater are required. Therefore, further consideration should be given to seaming adjacent geotextile panels when the sub grade shear strength is between CBR = 0.5 to 1.0.

Soil CBR Minimum
>3 0.9-1.5 feet
1-3 1.9-3.3 feet
0.5-1 3.3 feet or sewn
<0.5 sewn