Computational Techniques and Shear Band Development for Cylindrical and Spherical Penetrometers in Strain-Softening Clay
Publication: International Journal of Geomechanics
Volume 7, Issue 4
Abstract
This paper addresses numerical simulation of deep penetration of full-flow penetrometers in strain-softening, rate-dependent, cohesive soil, and the observed phenomenon of periodic shear bands. The analysis was conducted using a large deformation finite element approach, modifying the simple elastic–perfectly plastic Tresca soil model to allow strain-softening, with strain-rate dependency being incorporated in order to avoid spurious mesh dependency. Parametric analyses were carried out varying the strain-softening parameters (hence the relative brittleness of the soil), the rigidity index of the soil, and the strain-rate parameter. Increased brittleness of the soil led to reduction in the penetration resistance, but also to increasingly significant oscillations in the resistance–penetration responses. The oscillation was found to result from periodic shear bands evolving cyclically ahead of the advancing cylindrical and spherical penetrometers. Analyses with different values of rigidity index confirmed further that the periodic shear bands were a real material phenomenon, rather than due to errors in numerical simulation. Similar phenomena have been observed for continuous flow problems in granular materials. However, rising strain-rate dependency tended to suppress the oscillations.
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Acknowledgments
The work presented here forms part of the activities of the Centre for Offshore Foundation Systems (COFS), established under the Australian Research Council’s Research Centres Program. This research was motivated by involvement in the joint industry project: Shear Strength Parameters Determined by In Situ Tests for Deep-Water Soft Soils, undertaken jointly with NGI (project leader Tom Lunne). The writers would also like to acknow-ledge the benefit of discussions with Dr. Itai Einav and Edgard Barbosa-Cruz.
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Published In
International Journal of Geomechanics
Volume 7 • Issue 4 • July 2007
Pages: 287 - 295
Copyright
© 2007 ASCE.
History
Received: Oct 5, 2006
Accepted: Jan 9, 2007
Published online: Jul 1, 2007
Published in print: Jul 2007
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