Guideline for Determining the Improvement Factors and Design of Geocells in Road Building, Netherlands

New guideline emphasizes the key geocell parameters required for long-term road base reinforcement.

“Geocells must have the right properties when it comes to dynamic stiffness, resistance to plastic deformation and tensile strength…”

This published standard in the Netherlands is an excellent example of the growing trend to create standard guidelines for the use and design of geocells worldwide. It covers the required material properties and design principles that should be adopted to optimize geosynthetic reinforcement performance for pavements – and specifically for geocells.

This Guideline was written by a team of experts for SBRCURnet (CROW), highly respected Dutch institutes that develop guidelines and standards in the fields of civil engineering, road construction, and traffic engineering.

A key point of the document is that the extent of the reinforcing or stabilising effect is determined by the material from which the geocell product is made and the geometry. The most important material properties are elastic stiffness and resistance to permanent deformation (creep). The limit on plastic deformation for reinforcement synthetics is defined as low deformation, e.g., less than 2%. The actual effectiveness of base reinforcement is reflected in the support improvement factor (SIF) and the modulus improvement factor (MIF).

Click here to view a translated summary of the guideline
(All rights reserved to SBRCURnet and CROW, NL)

Highlights of Guideline

1. Elastic stiffness and resistance to permanent deformation – the most important material properties (para. 1.2.4):
“In addition to the structure of the road construction, the extent of the reinforcing or stabilising effect is determined by the material from which the product is made and the geometry. The most important material properties are the elastic stiffness and the resistance to permanent deformation (creep)…. Materials that exhibit a lot of creep will gradually lose their reinforcing capacity over time.”

2. Permitted accumulated geocell deformation – below 2% (para. 1.2.4)
“…Therefore, this type of base reinforcement is only effective if the deformations are limited to, for example, 0.5%. A distortion (elongation) of the geosynthetics of 2% horizontally will lead to many centimeters of distortion vertically in the road.

3. Geocell key properties determine the pavement reinforcement improvement factor (para. 2.2.4):

“The geocell mechanism provides an improved spread angle through the so-called “beam effect” (see Fig. 2-6).”

Table 2.5 – Global properties of reinforcement geocells*

PropertyUnitTesting methodValue
Dynamic stiffness modulus (net) (DMA-test)MPaEN-ISO 6721-1 ASTM E2254**
Cumulative plastic distortion (SIM test)% m/mASTM D6992<3
Tensile force, non-perforated cell wall (wide width)kN/mEN-ISO 1031920-29
Tensile force, perforated cell wall (wide width)kN/mEN-ISO 1031916-25
UV and Oxidation resistance (High-Pressure Oxidative Induction Time (HPOIT) at 150°CminutesASTM D5885> 400

*   values available only for geocells with rigid cell walls
** values depend on the application

Benefits

  • Provides best design methods and practices for geocell technology
  • Provides performance based factors for evaluating geocells
  • Geocell base reinforcement factor depends on elastic stiffness and resistance to deformation
  • Limits subgrade replacement and disruption
  • Reduces aggregate layer thickness
  • Enables use of inferior quality aggregate
  • Extended road design life reduces maintenance
  • Geocell reinforced base reduces deformation, extends design life
  • Reduces aggregate and placement costs
  • Reduces surface layer thickness, including asphalt