Evaluation of dropped versus static cone penetrometers at a calcareous cohesive site

Knowledge of the seafloor and its strength, characteristics is vital in the ocean engineering world. However, the in situ soil strength is very difficult to accurately determine with present conventional methods in the offshore environment, especially in deep water. Naval research has utilized both dropped penetrometers and quasi-static cone penetrometers incorporating an element to sense pore water pressure (“piezocones”) to attain such information. The Navy has developed a dropped penetrometer called the eXpendable Doppler Penetrometer (XDP). This penetrometer was originally designed to provide an undrained strength profile in soft, cohesive sediments by measuring the instantaneous velocity (and thus, deceleration) of a sound source probe as it falls through the water column and penetrates the seafloor. Correspondingly, a pressure sensitive, hydraulic piezocone has also been used to verify some of this data. The results of both types of tests are presented, and conclusions are drawn regarding the capability of the XDP to measure soil strength, as compared to the piezocone