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Site investigations were recently performed offshore at three prospective plat-form sites in water depths between 400 and 500 m in the Gulf of Mexico. Soil conditions at the sites generally range from very soft clays near the seafloor to very stiff clays at 120- to 150-m penetration. Analyses of stress history indicate the soils at these locations are generally normally consolidated. Laboratory tests were performed on recovered specimens to deter-mine the undrained shear strength. Standard laboratory miniature vane shear tests and unconsolidated-undrained triaxial tests were performed in addition to consolidated-undrained tests using stress history and normalized soil engineering properties (SHANSEP) procedures. Tests performed in the field included in-situ vane and cone penetrometer. Cone factors Nk were computed using in-situ vane shear strengths as the reference strength.
This paper compares the results of consolidated-undrained (SHANSEP) laboratory and in-situ tests to determine a relationship that may be used to correlate these results. The effects of soil strength and plasticity are examined and used to correlate shear strength with the liquidity index. A comparison is also made between peak and residual in-situ vane strengths.
This paper further describes how a combination of these in-situ and laboratory tests can be used to characterize a deepwater site for foundation design. Recommendations for future site investigations are also discussed.
clays, site investigation, in-situ vane, cone penetrometer, SHANSEP, liquidity index, plasticity index, normalized shear strength
Geotechnical engineer, Browning-Ferris Industries, Houston, TX
Project manager, McClelland Engineers, Inc., Houston, TX
Engineering department manager, S&ME, Inc., Fairfield, OH
Ocean engineer, Conoco, Inc., Houston, TX
Senior civil engineer, Shell Oil Company, Houston, TX