Free Fall Penetrometer Deployment Strategies and the Impact on Data Analysis: Pilot Weight Trigger versus Winch-Deployed-Paper

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The study compares pilot-weight-triggered and winch-driven deployments of the SEADART 1 free-fall penetrometer, assessing their effects on seabed-contact detection, penetration measurements, and data quality. The instrument combines a piezocone with accelerometers, an inclination sensor, and a mudline sensor.<br /><br />Tests were conducted in clayey sediments at two sites: approximately 135 m and 1,500 m water depth. At the shallower site, three deployments were released by a pilot-weight trigger from about 1 m above the seabed, while one was winched into the soil. At the deeper site, two deployments were winched throughout.<br /><br />Both strategies produced data suitable for geotechnical analysis, and deployment method had little apparent effect on penetration depth. At the shallower site, seabed contact was relatively easy to identify, particularly with the mudline sensor. At the deeper site, very soft soil made impact detection more difficult: several sensors indicated possible contact at different times. Reviewing the measurements together helped identify the most plausible impact point, which was supported by agreement between penetrometer results and nearby conventional cone penetration tests.<br /><br />The findings suggest that pilot-triggered and winched deployments can both yield high-quality data. However, contact identification may be challenging in very soft soils and potentially where fluid mud is present. The authors recommend further testing in sandier soils and consideration of instrument-shape modifications to improve impact detection. Both deployment approaches appear suitable for estimating geotechnical properties, including undrained shear strength.

Keywords

SEADART 1

free-fall penetrometer

pilot-weight trigger

winch-driven deployment

seabed contact detection

penetration measurements

data quality

piezocone

undrained shear strength

clayey sediments