Date of Award

Spring 2009

Project Type


Program or Major

Engineering: Ocean

Degree Name

Doctor of Philosophy

First Advisor

Jeffrey S Melton


A study was conducted to determine the penetration behavior of a cylindrical probe free falling to the seafloor and to utilize the data obtained to evaluate the engineering properties of surficial sediment. Two experimental probes, each equipped with accelerometers, pressure sensors and optical backscatter sensors were deployed in different sediment regimes. The data collected was used to derive the sediment type and determine physical properties such as undrained shear strength, coefficient of consolidation and shear modulus for soft fine-grained sediment.

Acceleration signals from drops of a free fall penetrometer contain information about the nature of the seafloor. A simple sediment classification model was proposed using data from field deployment tests as well as literature. This model, though applicable only to the probes used in this study, presents an approach that can expand the usage of free fall penetrometers.

Rapid penetration with rigid probes in saturated sediments usually results in an increase in measured penetration resistance. This effect, called the strain rate effect, was studied for soft fine-grained sediments by formulating a model to determine undrained shear strength profiles.

Excess pore pressure dissipation seen in post-arrest pressure sensor signals in fine-grained sediments were studied to predict the coefficient of consolidation and by extension permeability and shear modulus. A dissipation model using a cylindrical cavity expansion method was formulated for this purpose.

A field study was conducted to validate the sediment classification model and undrained shear strength models. Field vane shear tests at the location of the probe drops were used to validate the strain rate dependent strength model.

This work facilitates the expanded use of free fall penetrometers as part of geotechnical, geophysical and geological studies of the seafloor.