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

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Farhad Salour

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-theta model parameters from the backcalculated internal stresses and unboundlayers moduli, it was observed that the k1 parameter decreased with increasing moisture content for both the granular layer and the unsaturated subgrade materials.

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