Influence of rate effects, temperature and moisture content on the geomechanical behavior of marine clays

The study of the geomechanical behavior of marine clays is a basic requirement for project optimization of the oil and natural gas industry. As part of a large-scale project, this study explored the effects of moisture content, temperature and rate effects using laboratory vane shear tests. A series of results has helped in the identification of the effects of ground freezing on the undrained shear strength. For temperatures below freezing (−2.0°C) the undrained shear strength increases with increasing water content and decreases with increasing shear rates for applied angular velocities in the range of 0.0025 to 0.015 rpm. Apparently, with the freezing of pore fluids, the shear strength is partially governed by the strength of the ice-soil particle bonds. The increase in shear rate appears to facilitate the breakage of the ice-bonds and afterwards the ice crystals reducing the viscous effects on the mobilized shear strength. Conversely, samples tested at temperatures above freezing, show an increase in undrained shear strength with the increase in the imposed angular velocity, and decreases with increasing soil moisture. Based on these studies, it is concluded that rate effects should be coupled to the influence of temperature and moisture content in design of offshore structures.