A rational method of designing flexible pavements against shear failure using the Gyratory Testing Machine is described. In the specific procedure, the element of material in the GMT is considered to represent an element in the pavement structure. For the sample, the theoretical vertical stress becomes the normal load, and the measured shear stress represents the shear strength at the point for some selected strain. By comparing a plot of induced vertical (normal) stress vs. the induced shear stress with the measured shear for that induced normal shear, a Mohr type analysis is achieved for the in-situ stress at various depths below the load. Changes in loading can be readily evaluated by adjusting GTM parameters. Test procedure comprises three basic steps: 1. Determination of stress distribution; 2. GTM tests on sample set; 3. Analysis of data. The method is virtually identical for new design and for evaluation of existing pavements. For design tests it is important to simulate ultimate density and moisture conditions. By implementing GTM test methodology, optimum moisture and density for the anticipated design stress can be arrived at. Since in these methods both the compaction and shear tests can evaluate alternative (i.e. increasing) design loads, density and shear strength requirements will always be related to the anticipated traffic loading.
Abstract