Chart For Determining Equivalent Single-Wheel Loads

A new chart based on Burmister's layered theory programmed for a high-speed computer is developed for determining equivalent single-wheel loads for flexible pavements. The equivalent single-wheel load is defined as a single wheel load which results in a maximum deflection in the subgrade equal to that produced by a set of dual wheels. A salient feature of the chart is that it takes the ratio of the moduli of elasticity of the pavement and subgrade into account and presents the results of a wry involved problem in a simple manner. The equivalent single-wheel load for any combinations of pavement thickness, modulus ratio, wheel spacing, and contact radius can be obtained from the chart with simple calculation and interpolation. The chart shows that the equivalent single-wheel load increases appreciably with the increase in modulus ratio. Current practice of assuming pavements as homogeneous media always gives an equivalent single-wheel load which is too small and is not in line with the finding of the WASHO road test.