A series of consolidated un drained static and cyclic simple shear tests was conducted on highly over on soldiered silt from offshore California. The observed behavior indicates a tendency for initial contraction followed by dilation. As a result, the total stress path followed by in-situ soils has to be carefully considered in evaluating their performance under foundation loads.
A series of static and cyclic consolidated untrained simple shear tests was performed on high quality samples to investigate the stress-strain behavior and pore pressure response of highly over consolidated silt.
The test series was designed to yield information on:
The stress-strain behavior of the soil under static loading when reconsolidated to stresses approximately equal to those existing in-situ.
Pore pressure response during static shear.
Pore pressure generation and modulus degradation during cyclic simple shear.
Post-cyclic response to statically applied shear load.
The samples were obtained during a site investigation for an offshore platform in several hundred feet of water; The sampling was done from the Dames & Moore/Fugro drill vessel, the M/V Kara Seal, using the Fugro Offshore Drill Rig and Wipsampler. With the Wipsampler equipment, a thin walled tube of 2.8 inch inner diameter is attached to a down hole latching jack and hydraulically pushed into the soil at a steady rate of about 0.5 inch per second. During the sampling operation, the drill string is held stationary by a seabed resting clamp to assure drill string stability. Because the drill string is heave-compensated during both drilling and sampling operations, the sampled soil is subject to minimal disturbance, other than the disturbance caused by pushing of the tube and stress relief.
Recovered samples were taken to a shipboard laboratory, their lengths measured, and the bottoms and tops of the sample tubes cleaned out and trimmed to allow insertion of expandable O-ring washer seals. Sample tubes were capped and taped with electrical tape as an additional precaution against moisture content changes, and transported to the testing facility by motor vehicle.
The soil selected for testing is a highly overconsolidated Pleistocene silt. The general index properties, consolidation characteristics, stress history, and shear strength from triaxial tests are described by Villet and Darragh (1985). Similar soils are found over much of the Santa Barbara Channel and Santa Maria Basin areas (McNeilan and Bugno, 1984).