Sub-grade support: a review of short-term and long-term performance requirements

Sub-grade support: a review of short-term and long-term performance requirements

Subgrade performance is a function of a soil's strength and its behaviour under traffic loading. The subgrade should be stable to prevent excessive rutting and shoving during construction, provide good support for placement and compaction of pavement layers, keep pavement rebound deflections to acceptable limits, restrict the development of excessive rutting during the service life of the pavement and minimise effect of changes in moisture level.

In the case of weak subgrades, a capping layer of some thickness may be placed on top of the subgrade to facilitate field construction. This paper demonstrates that a semi-infinite effective subgrade stiffness can in fact be calculated for a combination of a capping layer and a semi-infinite subgrade. Furthermore, this paper discusses the importance of thickness and quality of capping layer, for both short- and long-term loading conditions. The recommended capping thicknesses have been benchmarked against the UK and US requirements.

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