Kenneth H. Stokoe, II
Spatial Profiling of the Subbottom with Interface Waves
Brent Rosenblad (PhD students)
Design and construction of foundations and pipelines in deep water requires knowledge of the geotechnical characteristics of the sites where these systems will be located. Conventional geotechnical exploration techniques, as used on the Continental Shelf, become quite limited in their utility in deep water. This effort is aimed at developing the technology and equipment for determining shear stiffness profiles from interface wave and seismic-cone measurements.
This project contributes to the development of innovative and cost-effective techniques for geotechnical site investigations in deep water. This area is one in which the seafloor thrust area is focusing. This effort will also contribute to investigations at the theme sites and other locations as opportunities arise.
This work builds on earlier research in which the utility of seismic interface waves (commonly referred to as SASW testing) was shown for nondestructive investigation of the seafloor. This work involves the development of procedures and instrumentation to optimize the use of interface-wave profiling at deepwater sites. Two significant constraints are that all instrumentation must be self contained and that it should be operated remotely. Additionally, other seismic measurements such as direct, refraction and/or reflection testing should be combined, to the extent possible, within the array used for the interface wave (SASW) measurements. Preliminary offshore testing will be conducted in shallower water as cruises of opportunity arise. Initial testing at the theme sites will be performed in concert with the other theme-site efforts in the thrust area. A significant push is being made to develop funding for this work through Joint Industry Participation.
An on-going study using interface waves is being conducted by Dr. Robert Stoll of Lamont-Doherty Earth Observatory of Columbia University with funding from the U.S. Navy. We have interacted with Dr. Stoll on one cruise in the Gulf of Mexico in August, 1993 when his source, receivers and recording equipment were employed. The potential of interface wave testing was clearly demonstrated in this work which occurred in about 30 m of water. The goal of our efforts is to develop equipment for water depths of 1500 to 3000 m.
This work has the potential to form a key part of in situ geotechnical site investigations for foundations and pipelines in deep water. The opportunity exists to develop shear stiffness profiles to depths tailored to the geotechnical problem; 2 to 5 m for pipelines and 30 to 100 m for foundations.
October 1994 to September 1998Reports documenting the results; Procedures amenable to deepwater investigations; First-generation (and possibly prototype) equipment for use in shallow water which can be developed into deepwater equipment with proper funding.
Wright, S.G., Stokoe, K.H., and Roesset, J.M., "SASW Measurements at Geotechnical Sites Overlaid by Water," Dynamic Geotechnical Testing II, STP 1213, ASTM, Philadelphia, 1994, pp. 39-57.
Luke, B.A. , "In Situ Measurement of Stiffness Profiles in the Seafloor Using the Spectral-Analysis-of-Surface-Waves (SASW) Method," Ph. D. Dissertation, University of Texas at Austin, December 1994.
Lee, B., "Analytical Studies of Surface Wave Propagation Along the Seafloor for Application to Spectral-Analysis of Surface-Wave (SASW) Testing," PhD Dissertation, University of Texas at Austin, May 1996, (supervised by S.G. Wright).