Undrained Stability of Braced Excavations in Clay
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 129, Issue 8
Abstract
Short-term undrained stability often controls the design of braced excavations in soft clays. This paper summarizes the formulation of numerical limit analyses that compute rigorous upper and lower bounds on the exact stability number and include anisotropic yielding, typical of -consolidated clays and bending failure of the wall. Calculations for braced cuts bound the actual failure conditions within ±5%, and highlight limitations of existing basal stability equations. The analyses clarify how wall embedment and bending capacity improve the stability of well braced excavations. Careful selection of mobilized strengths at shear strains in the range 0.6–1.0% are necessary to match the predictions of anisotropic limit analyses with nonlinear finite-element predictions of failure for the embedded walls. Two example applications from recent projects in Boston highlight the practicality of the numerical limit analyses for modeling realistic soil profiles and lateral earth support systems, but also focus attention on the need for careful selection of undrained strength parameters. Credible estimates of stability have also been obtained in reanalyzing a series of case studies reported in literature using isotropic strength parameters derived from field vane or laboratory simple shear tests.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 129 • Issue 8 • August 2003
Pages: 738 - 755
Copyright
Copyright © 2003 American Society of Civil Engineers.
History
Received: Sep 6, 2000
Accepted: Nov 6, 2002
Published online: Jul 15, 2003
Published in print: Aug 2003
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