Two separate studies were conducted involving Sub-grade reinforcement methods/materials. Their primary focus was upon the strength of the sub-grade reinforcement materials and their respective equivalency criterion. Brief summaries are below:
Equivalency of Sub-grade Materials/Methods: The objective of this equivalency study was to develop a method for selecting the thickness of four alternative materials used in lieu of “breaker run” crushed rock as a working platform for highway construction on very soft sub-grade. Breaker run is commonly used for working platforms, and thus was selected as the reference material. Three industrial byproducts (bottom ash, foundry slag, and foundry sand)and a granular backfill were used as alternative materials. A working platform of alternative material was considered equivalent to that with breaker run if the total deflection of the alternative material was equal to the total deflection of breaker run under the same construction loading.
Strength of Sub-grade Materials/Methods: The objective of this study was to develop a methodology for incorporating the structural contribution of a working platform into the AASHTO design method for pavements. Two approaches have been proposed for flexible pavements. In one approach, the structural contribution of the working platform is included by defining a structural number for the working platform as if it was a sub-base. In the other approach, the contribution of the working platform is included using a composite effective roadbed modulus. The structural number approach is more direct and is preferred. However, in some cases the structural number approach indicates that the working platform provides no structural contribution, whereas some improvement to the pavement system is expected when a strong working platform is placed on top of a soft sub-grade.
More information may be found in the following files: