Cyclic Behavior of a Deepwater Normally Consolidated Clay

by Rathindra N. Dutt, Fugro-McClelland Marine Geosciences, Inc, Houston, United States,
Earl H. Doyle, Fugro-McClelland Marine Geosciences, Inc, Houston, United States,
Richard S. Ladd, Fugro-McClelland Marine Geosciences, Inc, Houston, United States,

Document Type: Proceeding Paper

Part of: Civil Engineering in the Oceans V


A comprehensive advanced laboratory testing program was undertaken to study the cyclic behavior of clays under various combinations of one-way and two-way cyclic loading. This work was performed as part of the foundation investigation for the `Auger' tension leg platform to be installed in 872 meters of water in the Gulf of Mexico. Soils at the site are highly plastic, normally consolidated clays. Stress-controlled cyclic undrained direct simple shear (DSS) tests show that the number of cycles to failure decreases with an increasing cyclic stress ratio and an average shear stress ratio. Also, the maximum shear stress for samples tested with non-zero average shear stress exceeded the monotonic undrained shear strength of the sample. This discrepancy is shown to arise from the increase in static undrained shear strength due to anisotropic consolidation and strain rate effects. Post cyclic monotonic tests confirm previous findings which indicate that normally consolidated clays subjected to cyclic loading behave as overconsolidated material in subsequent monotonic loadings. Finally, comparison of the results from this study with other similar data on less plastic Boston Blue Clay and Drammen Clay suggests that the highly plastic clays at the TLP site are considerably more resistant to cyclic loading effects.

Subject Headings: Consolidated soils | Shear stress | Clays | Shear strength | Shear tests | Soil analysis | Soil strength | Soil stress | Gulf of Mexico | Boston | Massachusetts | United States

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