The Effect of Water Content on Light Weight Deflectometer Measurements

The application of modulus-based in-situ testing methods has been widely increasing for control of the compaction quality of earthwork construction in recent years. Since their introduction to the QA/QC process, it has been observed that there are several factors that influence the measured modulus of the soil, such as moisture content, influence depth, and temperature. To achieve more reliable test results, these factors should be accounted for in interpretation of the data. As noted by previous researchers, water content is one of the most important properties that affects the modulus measurements of compacted soil. To explore the sensitivity of measured modulus-based in-situ test results to the effect of compaction water content, a field study was performed in the State of Delaware in the summer of 2008. Two Light Weight Deflectometers (LWDs) were used in the study to measure compacted soil modulus values, one with a 300 mm contact plate diameter and one with a 200 mm plate diameter. The fill material tested during this study was a poorly graded sand with silt (SP-SM). The purpose of the current paper is to demonstrate the sensitivity of the measured soil modulus values to fluctuation in soil moisture content in the field, and to discuss possible approaches for interpreting this type of variable LWD data.