Falling Weight & Heavy Weight Deflectometer
Purpose
The Heavy Weight Deflectometer (HWD) is a non-destructive testing (NDT) device that provides realistic deflection basin parameters that can be used as an input into a mechanistic pavement model to quickly and adequately determine the structural condition of the pavement.
Methods
By means of a falling weight striking a specially design rubber spring system, the dynatest HWD produces an essentially half-sine shaped, single T “impact” load of 25 – 40msec in duration, closely approximating the effect of a moving wheel load of 50 kN or 700 kPa. A typical testing sequence in one measuring point is performed in less than 40 seconds. The deflections are measured with an absolute accuracy of better than 2% + microns and with a typical relative accuracy of 1 % + 1 micron. The resolution of the equipment (in terms of deflections) is 1 micron (1 micron = 0.001mm). The load is measured an accuracy of better than 2% + 0.3 kN.
Output
From the field test, HWD provides deflection values for certain interval. This data will be combined with layer thickness and traffic information to be analyzed using the multi-layer elastic program. From the analyzed data, the following outputs will be obtained:
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Strength of each pavement layer
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Subgrade CBR (California Bearing Ratio)
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Residual life or the road pavement
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Overlay thickness
