Robert B. Gilbert

Reliability of Foundations for Deep Water Facilities

Scot Weaver (MS student), Bob Albrecht (UG student)

What can be gained from geophysical information in evaluating geotechnical properties at deep water sites?
How reliable are site characterization models?
How does uncertainty in soil properties affect the reliability of foundation designs?
How can the value of information from an investigation program be maximized?

This project focuses on modeling site characteristics to serve as input to a reliability-based design approach for deep water foundations.

1) Develop correlations between geotechnical properties and geophysical data
2) Assess the reliability of geophysical data
3) Develop an analytical methodology to combine uncertain information from different sources (e.g., seismic surveys and back-analysis of existing slopes on the sea floor)
4) Quantify uncertainties in inferred geotechnical properties
5) Evaluate how uncertainties in soil properties affect foundation reliability
6) Apply methodology to theme sites

This work utilizes the field and experimental work being conducted by other investigators within OTRC to characterize the theme sites. Data will also be obtained from a proposed offshore testing program in Gulf of Mexico at a platform site.

Conventional geotechnical investigation techniques will be difficult at deep water sites, and the industry's experience base for geotechnical properties is minimal. This work will help to address these limitations by quantifying what can and cannot be ascertained from indirect information, such as geophysics. Further, it will provide a basis for designing investigation programs to optimize the value of information.

October 1994 to September 1997

Computer Program to Interpret Geotechnical Properties

Acquaah, C. G., "General Reliability Analysis of a Tension Leg Platform," M.S. Thesis, The University of Texas at Austin, 1995.
Gilbert, R. B. and Tang, W. H., "Model Uncertainty in Geotechnical Reliability and Decision Analysis," ICASP, Paris, 1995.
Gilbert, R.B. and Tang, W.H., "Model Uncertainty in Offshore Geotechnical Reliability," OTC, Houston, 1995.
Gilbert, R.B., Wright, S.G. and Liedtke, E., "Uncertainty in the Back analysis of Slopes," Uncertainty in the Geologic Environment: From Theory to Practice, ASCE, Madison, 1996.
Gilbert, R.B. and McGrath, T.C., "Site Investigation Design for Geotechnical Engineering," Book Chapter in Uncertainty Modeling in Civil Engineering, CRC Press, in press. Blake, W.D. and Gilbert, R.B., "Inferring Undrained Strength from Shear Wave Velocity for Normally Consolidated Clays," Offshore Technology Conference, in press, May 1997.
Ongoing cooperative research with Mobil Oil Co. and Unocal Corp.