The Influence of Groundwater Level on the Structural Behaviour of a Pavement Structure Using FWD

Abstract

The effect of groundwater table level on the structural response of an
instrumented flexible pavement in southern Sweden was studied using multilevel Falling
Weight Deflectometer (FWD) testing. In order to raise the groundwater table level under the
pavement structure, the outlets of the pavement’s subsurface drainage system was blocked for
three months. Thereafter, it was unblocked, allowing the pavement to recover to its normal
draining condition. During this period, variations in the groundwater level and subsurface
volumetric moisture content were registered. Manipulation of the drainage system
significantly affected the ground water level and the pavement unbound layers moisture
conditions. Both the granular layer and the subgrade stiffness significantly decreased with
increasing moisture content. In all the FWDs performed, the granular materials exhibited
stress-hardening behaviour. However, the subgrade showed stress-softening response in
unsaturated condition and stress-independent behaviour in saturated state. In an attempt to
determine the k  model parameters from the backcalculated internal stresses and unbound
layers moduli, it was observed that the k1 parameter decreased with increasing moisture
content for both the granular layer and the unsaturated subgrade materials.