Comparison of Multiple Sensor Deflection Data From Lightweight and Falling Weight Deflectometer Tests on Layered Soil

Abstract

The lightweight deflectometer (LWD) and falling weight deflectometer (FWD) are in situ dynamic plate load tests used to estimate the stiffness and elastic moduli of bound and unbound materials. The inclusion of radial offset sensors with LWD testing stemmed from the well-established FWD testing method of using deflections at the load plate center and at radial offsets to generate a deflection bowl to estimate the moduli of individual layers in a multi-layer system. Due to the similarities between the LWD and FWD tests, several studies have explored the relationship between center deflection results of the two tests. However, little research exists in the literature addressing LWD testing with multiple sensors and how well those deflections correlate with FWD deflections at the same radial offsets. To this end, 114 multiple sensor LWD and FWD tests were performed on stabilized base materials at three sites and rigorously analyzed to determine if there is a consistent relationship between LWD and FWD center and radial offset deflections across all sites and if the estimated moduli from the same backcalculation approach produce similar or correlated results. The results demonstrated that while relationships are site specific for deflections and moduli estimated from the load plate center, a consistent relationship across all sites is demonstrated from the radial offset measurements. Finite element analysis was conducted to understand the difference in induced strains from the two tests to support and better understand the observed differences in FWD and LWD deflections and backcalculated layer moduli.