Depth-dependent small-strain stiffness in embankment layers: Comprehensive field and laboratory studies

The evaluation of embankment layers plays a critical role in geotechnical engineering, prompting efforts towards geological investigation techniques. This study evaluates the relative density using three distinct methods: field density test, dynamic cone penetration test, and shear wave velocity measurements. The embankment layers are compacted in four different relative compaction R_C = 61 %, 80 %, 90 %, and 95 % while the average water content is ω = 11.2 %. The field density test and shear wave velocity are measured at every 1 m, and the dynamic cone penetration tests are conducted at a final embankment height H = 5 m. The relative density profile derived from DCPI provides a sensitive depth indicator. In addition, the earth pressure cells embedded at 2.5 m depth from the top of the 5-m embankment tracks changes in the effective stress during the embankments and facilitates the effective stress-dependent data analyses. We select the appropriate maximum and minimum void ratios to compare the relative density and relative compaction based on the laboratory test results. Laboratory oedometer tests with a movable-ring system provide model parameters for depth-dependent properties analyses. Finally, the shear wave velocity provides a method for estimating the relative density and bridging the gap between stress-based and depth-based field interpretations. These findings suggest that the shear wave velocity is a good indicator to assess the relative density evolution, plays a critical role in long-term monitoring and provides in-situ small-strain stiffness for seismic designs.