The load plate may be solid or segmented. In some FWDs the magnitude of the applied load pulse is an assumed constant value determined by system design in others the force is measured by load cells. Deflection sensors are used to measure the deformation of the pavement in response to the load pulse. Data are acquired from various sensors for use in post-test analysis of pavement properties. The load pulse is produced by dropping a large weight onto a "buffer" which shapes the pulse, and then transmitted to the pavement through a circular load plate. Comprehensive road survey vehicles typically consist of a FWD mounted on a heavy truck together with a ground-penetrating radar and impact attenuator.ĭuring testing, a FWD subjects the pavement surface to a load pulse which simulates the load produced by a rolling vehicle wheel. Depending on its design, a FWD may be contained within a towable trailer or it may be built into a self-propelled vehicle such as a truck or van. The data acquired from FWDs is primarily used to estimate pavement structural capacity, to facilitate overlay design or determine if a pavement is being overloaded. A falling weight deflectometer, towed by a truckĪ falling weight deflectometer (FWD) is a testing device used by civil engineers to evaluate the physical properties of pavement in highways, local roads, airport pavements, harbor areas, railway tracks and elsewhere.
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