Porewater Pressure in Clays Below Caisson Islands

by D. E. Becker, Golder Associates, Calgary, Alberta, Can,
M. G. Jefferies, Golder Associates, Calgary, Alberta, Can,
S. B. Shinde, Golder Associates, Calgary, Alberta, Can,
J. H. A. Crooks, Golder Associates, Calgary, Alberta, Can,

Document Type: Proceeding Paper

Part of: Civil Engineering in the Arctic Offshore


Unfrozen lightly overconsolidated clays are a significant factor in the design and performance of exploration caisson retained islands in the Canadian Beaufort Sea. At two sites (Tarsiut and Kadluk) the porewater pressures in the soft clay foundations were observed to increase significantly over periods of several months following completion of construction. These observations give rise to concern because, in conventional geotechnical experience, increasing porewater pressures are associated with strength decrease and reduced stability. The construction history of these islands and the performance of the respective foundation clay materials are discussed. The results of stress analyses are presented together with possible explanations for the observed time-dependent increase in excess porewater pressure following the end of loading. Based on these hypotheses, the significance of the observed porewater pressure behaviour with respect to strength and stability is discussed.

Subject Headings: Soil pressure | Pore water | Pore pressure | Clays | Islands | Caissons | Offshore structures | Stress analysis | Beaufort Sea

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