Numerical Modeling of the Test Pit for Falling Weight Deflectometer Calibration
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2021-11-24
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Edition:Final report (November 19, 2020 - November 24, 2021)
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Abstract:Montana Department of Transportation (MDT) planned to replace the soft clay layer of their test pit for Falling Weight Deflectometer (FWD) calibration with a geofoam layer hoping to increase the operational lifetime of the test pit. In this research, the possibility of replacing the clay layer with a geofoam layer was investigated using dynamic response analyses. A three-dimensional explicit finite volume model was developed and calibrated using the results of previous calibration tests conducted by MDT. The model was then used to determine if the geofoam can be used instead of clay as the soft layer in the FWD calibration test pit. Based on the results of the numerical models, it was concluded that geofoam can be used instead of the clay layer. In fact, 30 different setups were designed using two types of geofoam, i.e., EPS 19 and EPS 29. A decision matrix analyses approach was proposed to rank these designs from best to worst based on five criteria, i.e., AASHTO R32-11 maximum deflection requirements, reducing the possible noise, proper damping, construction cost, and variability. Based on the proposed decision matrix analyses it was determined that the best 12 ft wide-15 ft long geofoam setup would be composed of a 28 (in.) thick geofoam EPS 19, overlaying 3 (in.) of sand at the bottom of the test pit, and 23 (in.) of sand above the geofoam layer. A 5 (in.) thick concrete slab would be placed on the top of this setup.
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