Analysis and synthesis of subgrade stress and strain measurements for single layer unpaved roads

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University of New Brunswick


A series of tests were performed at the Transport Research Laboratory in Crowthorne, Berkshire, England for research by Prof. R. Douglas, DC. Campbell Chair in Highway Construction and Pavement Research at the University of New Brunswick. The purpose of these tests was to analyse the subgrade stress and strain response of a single layer unpaved road with the three variables being layer thickness, tire pressure, and wheel load. Rutting on the surface of unpaved roads had been observed after vehicles with inflated tire pressures passed over them. Therefore the initial objective of this report was to place stress and strain gauges in the clay subgrade to check if this rutting was caused by significant stress and strain increases in the subgrade. The other objective was to analyse the effects on the life of a single layer unpaved road by altering the three variables mentioned above. The testing procedures involved using layer thicknesses of 200mm, 350mm, and 560mm, tire pressures of 50psi and lOOpsi, and wheel loads of 45kN and 80kN. The stress and strain gauges were placed in a subgrade of gault clay (common to England) at varying depths. This report outlines the results of the testing and the effects the various combinations have on the life of a single layer unpaved road. The results could prove beneficial to those operating on unpaved roads, specifically in the forestry and mining industries.