INCLUSION OF DEPTH TO A RIGID LAYER IN DETERMINING PAVEMENT LAYER PROPERTIES . THIRD INTERNATIONAL CONFERENCE ON BEARING CAPACITY OF ROADS AND AIRFIELDS. PROCEEDINGS, NORWEGIAN INSTITUTE OF TECHNOLOGY, TRONDHEIM, NORWAY, JULY 3-5 1990. VOLUMES 1-2

This paper proposes a procedure for the improved calculation of elastostatic moduli by using the actual depth to a rigid layer in the analysis of nondestructive deflection data. A rigid layer need not be a rock layer; it can be any stiff material or a subgrade in which the effective stiffness increases with depth. Several methods were investigated for evaluating the effect of depth to a rigid layer of falling weight deflectometer (FWD) deflections. It was decided to adapt an approach suggested by Ullitz, applying a concept in Boussinesq's equations for deflection from a point load on an infinite halfspace. The mathematical calculations allowed for the fact that a pavement system generally contains layers of stiffer materials over layers of softer materials. An extensive field study was conducted in Texas, USA, which determined the stratigraphy of four test sections by coring to a depth of 4 m. The calculation procedure was verified by comparing the estimated depth to a rigid layer with the value obtained by using penetration tests and a seismic analysis. It was found that the most realistic backcalculation results were obtained when the analysis used the actual depth to a rigid layer. (TRRL)