Groundtruth results for dynamic penetrometers in cohesive soils

Dynamic soil penetrometers are used increasingly as a handy tool for rapid seafloor soil strength profiling. The U.S. Navy has developed a dynamic penetrometer called the expendable Doppler Penetrometer (XDP) as an effective tool for determining in-situ soil strength in deeper water depths. The XDP data are used to estimate the profile of undrained shear strength in cohesive sediments, and the profile of friction angle and relative density in cohesionless soils. It accomplishes this by measuring the instantaneous velocity of a sound source probe as it falls through the water column and penetrates the seafloor. Soil strength is determined from the rate of velocity change of the penetrometer as it enters the seafloor and comes to rest. Over the past 2 years, three site surveys provided extensive data sets of XDP and collocated core measured strength profiles. The results indicate good agreement between the average strengths measured by the vane and the XDP. The strength profiles (strength vs. depth) from the XDP and vane also have good agreement, except where cohesionless soil lenses are present within the cohesive matrix. The results also provide groundtruth databases for additional comparisons and analyses.