J.P. Giroud and Jie Han
Since its publication in 2004, the Giroud-Han design method for geosynthetic-reinforced unpaved roads has received considerable attention from the geosynthetics industry. This article is the second of two that provides practical information for the users of the method as well as for those who want to learn about the method. Click here for Part 1: Method development and calibration
Part 2 | Recommendations for the proper use of the method
Since its publication, the Giroud-Han (G-H) method (Giroud and Han, 2004a, b) has been used to design many geosynthetic-reinforced unpaved roads, generally with success. However, sometimes the method has been a victim of its success. Some users have adopted the method without fully understanding the assumptions made during its development and often ignoring its limitations. As a result, unsatisfactory results have sometimes been obtained and some misleading conclusions have been drawn in practice and publications. In addition, some issues have arisen from the widespread use of the G-H method; therefore, it is necessary to discuss and address these issues. The objective of this article is to provide recommendations for the proper use of the method. Recommendations are made regarding subgrade strength, base strength and stiffness, filtration requirements, geogrid properties, reliability, and method of verification.
A companion article by Giroud and Han was published in the February/March 2012 issue of Geosynthetics, which summarizes the development and calibration of the G-H design method. All of the equations mentioned in this article are numbered according to the equations in Part 1 (i.e., 9, 7, 8, 2, 1) and all equations (1–9) can be found in that February/March companion article.
The G-H method assumes that the subgrade consists of saturated fine-grained soil (silt and clay) and that it fails under an undrained condition. In some cases, the subgrade is unsaturated and not necessarily a fine-grained soil. This fact must be taken into consideration prior to use of the G-H method. The strength of unsaturated subgrade may drop significantly after soaking. The strength of a soaked subgrade should be used as a design input if an unpaved road is likely to become soaked during its design life.