Back-Calculation of Parameters for Slab on Two-Layer Foundation System

Abstract

Most highway and airport rigid pavements constructed today consist of a subbase layer, giving rise to a system of a concrete slab supported on a two-layer foundation. This paper makes use of the solution of a slab on a two-layer system to derive a closed-form procedure for back-calculation analysis of pavement parameters. A computer program called NUS-DEF3 to solve for surface deflections is developed as a subroutine in the back-calculation analysis. The algorithm for the closed-form back-calculation of this system is presented. This algorithm reduces a system of three equations with three unknowns to one single nonlinear equation. It differs from the conventional approach of searching for the best solution iteratively by means of the least-squares method, and gives unique closed-form solutions without the need to select an initial modulus to start with. Solutions to numerical examples of three typical slab-on-two-layer-foundation problems are presented.