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 s
lab on a two-layer system to derive a closed-form procedure for back-c
alculation 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 b
ack-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 t
he best solution iteratively by means of the least-squares method, and
gives unique closed-form solutions without the need to select an init
ial modulus to start with. Solutions to numerical examples of three ty
pical slab-on-two-layer-foundation problems are presented.