Key Points and Part 2 on the Giroud-Han Design Method in Geosynthetics Magazine
As discussed in a prior post, the February/March issue of Geosynthetics magazine includes an article that is of monumental importance to the use of geogrids in roadway design. The article was written by Dr. J.P. Giroud and Dr. Jie Han, the developers of the Giroud-Han method and two of the preeminent figures in the world when it comes to geosynthetics. Part 2 of the article has just been published in the April/May issue of Geosynthetics. It covers the use of the method.
Some key points from Part 2 of the article:
- Sensitivity of the method to subgrade strength is very high for subgrade CBR values below 1%. Therefore, it is imperative that designers properly assess subgrade strength and variability as conditions get softer to ensure that adequate layer thickness is provided.
- When conducting full scale trafficking studies to validate geosynthetic performance, it is critical that the construction practices used are realistic and that the effects of construction on subgrade strength are properly understood. Giroud and Han discuss one study in particular that has been widely discussed but is subject to significant questions regarding its validity due to this issue.
- The base thickness in the method is the compacted base thickness, not the thickness of the aggregate when the lift(s) are placed.
- The quality of the aggregate used is critical to the success of the method. (This is an area that has received too little attention in the past, but its importance is now being noticed by the research community.)
- There is no correlation between tensile strength at relatively high strains (2% -5%) and performance of mechanically stabilized sections. A correlation at lower strains may exist, but has not yet been demonstrated.
- The effectiveness of geogrid-aggregate interlocking varies by geogrid type, and appears to be the critical factor in maximizing the stiffness of the composite layer.
The Giroud-Han method is the accepted state-of-the-art for the design of unpaved roads using geosynthetics. As a designer, I encourage you to make use of it, because it provides the greatest precision and design certainty. But as with any engineering method, it is critical that everyone who uses it understands the underlying research and the limitations of the method’s applicability. These articles provide great information for designers and specifiers regarding what is required to use the Giroud-Han method properly.
You can read the article here: http://bit.ly/KqxsV3