October 4, 2018

Best Practices for Zero Retaining Wall Failures - Geogrid Reinforcement Requirements and Certification


There are many different international manufacturers that are supplying geogrid reinforcement, and they are not all equal. It is important to understand what influences the durability of the geogrid. The U.S. Federal Highway Administration identified three key factors:

  •        Soils that have a pH of 10 or more represent an environment that could potentially degrade the geogrid faster especially in the presence of enough water.
  •        Polyester molecular weight – the size of the polymer molecule has a significant influence on the chemical durability.
  •        Polyester carboxyl end group (CEG) – grids are less susceptible to degradation when they have fewer CEG in their molecular structure.
NCMA adopted the guidelines that the FHWA set for geogrid reinforcement. All polyester geogrids submitted for approval must be made of polyester fiber that meets the following specifications:

  •        Molecular weight greater than 25,000 g/mol
  •        Caboxyl End Group less than 30 mmol/Kg
The certification, obtained from the geogrid manufacturer, must originate from the actual manufacturer of the fiber to show conformance with the specification. (ref. BP, Chapter 7.1)

Allan Block is working to achieve our industry initiative of Zero Wall Failures. With our Best Practices Manual and experience in the industry we are trying to expand the knowledge base for the design of segmental retaining walls (SRW's) by communicating and educating the professionals in the industry.  To see the full Best Practices Manual, visit allanblock.com to download today and keep an eye out for more industry Best Practice recommendations here.