Curvilinear Behavior of Base Layer Moduli from Deflection and Seismic Methods

The reality of curvilinear relationships of stiffness versus deformation is usually neglected when moduli values from seismic methods are compared with those of deflection methods. On the basis of extensive field testing, results showed that moduli values for the base layers from deflection methods did not conform to those of seismic methods. Deflection testing techniques were signified by the falling weight deflectometer (FWD) and the Dynaflect methods. Seismic testing was carried out by use of the seismic pavement analyzer (SPA) method. The SPA test results yielded moduli values higher than those obtained from the deflection methods. Utilizing pavement parameters obtained from the SPA data, researchers determined surface deflections by use of frequency response functions of signals from the two groups of sensors used in the testing setup. Because of the types of hammers in the SPA testing, two different deflection basins were obtained at each testing point. Comparison of surface deflections from these methods indicated that deflection amplitudes from the FWD method were about 100 times higher than those obtained from the high-frequency hammer of the SPA. At certain pavement sections, deflections from the Dynaflect method were comparable to those obtained with the SPA low-frequency hammer. Accordingly, curvilinear relationships between surface deformation versus stiffness values were derived. These relationships can be used to determine moduli values at all surface deflections, including those from service loads.