This document discusses the application of linear elastic layer theory and backcalculation to evaluate flexible pavements. It describes how a falling weight deflectometer can be used to measure the deformation of a pavement under a load and at different radial distances. Linear elastic layer theory can then be used to model the surface deflections based on pavement properties like layer moduli and thicknesses. Backcalculation is used to determine the modulus values of layers by minimizing the difference between measured and modeled deflections. Genetic algorithms and ant colony optimization have also been applied to backcalculate pavement moduli.

1. Applications in Civil Engg.
Vamsidhar Tankala & Shrey Modi
Department of Civil Engineering,
IIT Kharagpur

2. Pavement Evaluation
Load
d
r

3. FWD (Falling weight
deflectometer)
 On application of
load, the flexible
pavement deforms
and this
deformation (d) can
be obtained at
various radial
distances (r) by
FWD

4. Linear Elastic Layer Theory
 The surface deflections can also be
found from linear elastic layer theory.
 Inputs required:
 Modulus values
 Thicknesses Pavement Properties
 Poission ratios
 Radial Distances
 Load, Tyre pressure etc

5. Pavement Evaluation
Linear elastic layer theory
Pavement properties Surface deflections
(Forward calculation)
(Back calculation)

6. Problem Statement
 Given:
 Surface deflections at various radial
distances (obtained from FWD) (D)
 Poission ratio values
 Layer thicknesses
 Find Modulus values of the layers
 Minimizing the difference between
given and obtained deflections (Linear
Elastic Layer Theory)

7. Problem Statement
 ∂i = actual deflection at point ‘i’
 di = deflection from Linear elastic
Layer Theory at point ‘i'
 Objective Function:
 OBJ Fn = ∑ | ∂i – di |
 Minimize the OBJ Fn!!

8. Some of the MANY other
works in Civil Engg.
 Backcalculation of pavement modulus
using Genetic Algorithms and ACO
 Achieving best traffic parameters in a
simulation using Evolutionary Algos.
 Site Layout of Temporary Construction
Facilities using ACO
 Discrete optimization of Trusses using
Ant Colony Metaphor
 Vehicle Routing Problem using PSO