Analysis of simple shear tests with cell pressure confinement

ABSTRACT

The high cost of offshore infrastructure provides continuous encouragement for optimisation of design practices. Development of a more rational method to interpret results from simple shear tests with cell pressure confinement can reduce costs and improve reliability of offshore infrastructure. This paper addresses a commonly overlooked issue affecting design parameter selection: specimen shape varies from right cylinder to oblique cylinder after loading along a single shearing direction. Thus, horizontal stresses are not always equal to the cell pressure and their magnitude varies throughout the specimen’s lateral surface. An analysis is proposed that accounts for changing specimen geometry and lateral surface area during shearing and for the actual effect of cell pressure during testing. The analysis also describes how the intermediate principal stress can be assessed. Test results for medium dense silica sand are interpreted following de Josselin de Jong’s alternative shearing mechanism hypothesis. Conventional interpretation methods yield conservative design parameters for this soil. Failure states develop when the intermediate principal effective stress is halfway between major and minor principal effective stresses. Typical results for the soil tested show equipment performance meets standard direct simple shear requirements for shear strain rate, vertical stress and specimen height control.

KEYWORDS:

• laboratory test
• plane strain
• intermediate principal stress
• principal stress rotation
• offshore sediments

Acknowledgements

This work forms part of the activities of the Centre for Offshore Foundation Systems (COFS). Established in 1997 under the Australian Research Council’s Special Research Centres Program. Supported as a node of the Australian Research Council’s Centre of Excellence for Geotechnical Science and Engineering (ID CE110001009), and through the Fugro Chair in Geotechnics, the Lloyd’s Register Foundation Chair and Centre of Excellence in Offshore Foundations and the Shell EMI Chair in Offshore Engineering. The author is supported through ARC grant CE110001009.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work was supported by the Australian Research Council [CE110001009].