Influence of Wheel Load Shape on Vertical Stress Reaching Subgrade through an Aggregate Layer
COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
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The U.S. Army design procedure to stabilize low-bearing-capacity soil with geotextiles is based on the assumption that the applied surface load the wheel load is in the shape of a circle. The maximum vertical stress that reaches the subgrade through overlying aggregate is then estimated on the basis of the assumption that the aggregate is an elastic,homogeneous, isotropic half-space and, therefore, that the stress distribution can be estimated by using the Boussinesq method. To study the extent to which the shape of the applied load influences the stress that reaches the subgrade through the aggregate layer, the maximum vertical stress at depth predicted by the Boussinesq method was computed and compared for circular and rectangular loads. A comparison of the maximum vertical stress beneath circular and rectangular loads as a function of depth indicated that the differences were insufficient to warrant a change in the design procedure for rectangular load geometries that have lengthwidth ratios of 3 or less, and, furthermore, that assuming that the load is circular is conservative. For length width ratios of 3 or less,the maximum vertical stress applied by a rectangle is at least 85 of that applied by a circle.