Surface coring for shear strength measurements

Abstract

Gravity and piston coring equipment and methods currently in use for obtaining quality surface samples of fine-grained soils from the ocean floor are evaluated in terms of disturbance affecting the shear strength. The methods are applicable to shallow-water sites, but since conventional drilling and sampling techniques are successful in shallow water, emphasis is placed on the recovery of samples from very deep water. Reasons for sample disturbance are cited to indicate features that should be considered in the design of samplers to minimize disturbance. Accepted standards for the design of samplers are reviewed and summarized. It is concluded that conventional marine piston samplers have undesirable features that disturb cores more than the disturbance encountered in properly designed open-barrel gravity samplers. A table summarizes the relationship between the sample quality and the method of sampling. (78 refs.)