Foundation, Concrete and Earthquake Engineering

Limitations of Geogrid

Geogrids are planar product manufactured from polymeric material and typically placed in soil to form an integral part of a drainage, reinforcement, or stabilization system. It contains relatively high strength polymer grids consisting of longitudinal and transverse ribs connected at their intersections.

It can be either biaxial or uniaxial, depending on the size of the apertures and shape of the interconnecting ribs. As geogrids are continuous, they tend to transfer and redistribute stresses away from areas of high stress concentrations (such as beneath a wheel load). Some of the limitations of geogrid are as follows:

1. Ultraviolet Light. 
Even geogrids produced of carbon black (i.e., ultraviolet stabilized geogrids) can degrade when exposed to long-term ultraviolet light. It is important to protect the geogrid from sunlight and cover the geogrid with fill as soon as possible.

2. Non-uniform Tensile Strength. Geogrids often have different tensile strengths in different directions as a result of the manufacturing process.
For example, a Tensar SS-2 (BX1200) biaxial geogrid has an ultimate tensile strength of 2100 lb / ft in the main direction and only 1170 lb / ft in the minor (perpendicular) direction. It is essential that the engineer always check the manufacturer’s specifications and determine the tensile strengths in the main and minor directions.

3. Creep. Polymer material can be susceptible to creep. Thus, it is important to use an allowable tensile strength that does allow for creep of the geosynthetic. Oftentimes, this allowable tensile design strength is much less than the ultimate strength of the geogrid. For example, for a Tensar SS-2 (BX1200) biaxial geogrid, the manufacturer’s recommended tensile strength is about 300 lb / ft, which is only one-seventh the ultimate tensile strength (2100 lb / ft). The engineer should never apply an arbitrary factor of safety to the ultimate tensile strength, but rather obtain the allowable geogrid tensile design strength from the manufacturer.

No comments:

Post a Comment