Energy Conservation as a Principle Underlying Mobilizable Strength Design for Deep Excavations
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 137, Issue 11
Abstract
Finite-element analyses (FEA) and case histories of deep excavations in soft clay are used to validate a decision-making tool based on an extended mobilizable strength design (MSD) method that permits the designer an extremely simple method of predicting ground displacements during an undrained excavation. This newly extended MSD approach accommodates a number of issues that are important in underground construction between in situ walls, including alternative base heave mechanisms suitable either for wide excavations in relatively shallow soft clay strata or narrow excavations in relatively deep soft strata, the influence of support system stiffness in relation to the sequence of propping of the wall, and the capability of dealing with stratified ground. In addition, a simplified MSD framework is proposed for analyzing a database of 110 deep excavation case histories worldwide. The approach examines the governing factors controlling deformation in deep excavations and offers simple guidelines for designing support structures for deep excavations. These developments should make it possible for a design engineer to make informed decisions on the relationship between prop spacing and ground movements or the influence of wall stiffness and on the need for and influence of a jet-grouted base slab, for example, prior to conducting project-specific FEA.
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Acknowledgments
The writers would like to acknowledge the Platform Grant (UNSPECIFIEDGR/T18660/01) awarded by the UK Engineering and Physical Sciences Research Council. We were alerted to the extensive field records of excavations in Shanghai through a presentation by Dr. Xu of Eastern China Architectural Design and Research Institute (ECADI) at an Engineering and Physical Science Research Council (EPSRC) UK–China GEONET meeting in Ningbo in September 2008. We are grateful to Dr. Xianfeng Ma for help in translating key terms in Dr. Xu’s Ph.D. thesis.
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© 2011 American Society of Civil Engineers.
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Received: Aug 24, 2009
Accepted: Jan 14, 2011
Published online: Jan 17, 2011
Published in print: Nov 1, 2011
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