Foundation problems for drilling structures offshore from Louisiana are related to the shearing strength and scour resistance of near-surface late Quaternary Continental-Shelf deposits. Over much of the shelf area, thick topstratum clays provide the foundation materials; where clays are thin, underlying substratum sands or weathered late Pleistocene deposits constitute the foundation. Study of the nature of the late Quaternary facies and of their relation to shelf topography makes it possible to map the sediment types and to date them. Compression tests on clay samples permit recognition of four categories of strength variation with depth: normally consolidated, underconsolidated approaching normal, underconsolidated, and overconsolidated clays. These tests also demonstrate that substantial time is required for clays to reach a normally consolidated condition.

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