STUDY OF PARAMETERS AFFECTING IMPULSE-RESPONSE METHOD

Even though the impulse response method is widely used in detecting de fects under rigid pavements, the sensitivity of the method is not well understood. Modal time-history analyses were used to numerically simu late the impulse response method. Parameters such as the thickness and the elastic modulus of the slab, the modulus of subgrade of the soil, the length and width of the slab, location of the impact, and size an d location of defects were studied, The sensitivity of flexibility spe ctrum, the major function measured in the field to detect defects, to each of these parameters was studied. It was found that the elastic mo dulus and dimensions of the slab have small effects, while the thickne ss of the slab and the modulus of subgrade more significantly affect t he flexibility spectrum. For most practical applications, corner voids that are twice the thickness of the slab should be detectable. For ed ge and midslab, the defect has to be four and five times the slab thic kness (respectively) to be detectable.