Assessment of HWD Ability to Detect Debonding of Pavement Layer Interfaces

Abstract

Usual Falling or Heavy Weight Deflectometer (F/HWD) backcalculation methods assume that pavement layers are fully bonded. In order to assess the ability of HWD testing to detect debonding of the interfaces between pavement layers, the French civil Aviation technical center (STAC) performed an HWD campaign on the circular Accelerated Pavement Testing (APT) facility of IFSTTAR in Nantes, on an experimental pavement with artificially created local sliding interface between bituminous surface and base layers. Both the sound and the defective tested pavement sections present a common structure in terms of subgrade, materials and layer thicknesses. HWD tests have been performed along a large circular arc covering the two sections. A fine spatial measure discretization (10 cm) was used. The experimentation shows that the HWD is a valuable tool for the detection of extended interface defects detection, the central deflection being significantly affected by the interface quality, the outer deflections being less sensitive to this parameter. This paper presents raw deflection results, allowing to precisely locate the underlying defects in the test section. Then a numerical study is detailed, which aims at assessing the effect of the bonding conditions over deflections. The theoretical analysis of this HWD survey is performed in two steps: firstly, on the basis of the finite elements method (FEM) dynamical modeling of the HWD test developed by the STAC, a backcalculation of material moduli is performed using the deflections measured in the sound area. Secondly the backcalculated moduli are introduced in a forward calculation, taking into account the debonded interface. The numerical results are compared with experimental deflections measured over the defects. They are consistent with in situ results.