Prediction and Performance of Deep Excavations for Courthouse Station, Boston
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 141, Issue 4
Abstract
Construction of the Silverline Courthouse Station in South Boston involved 18-m-deep excavations at a site underlain by more than 24 m of normally and lightly overconsolidated Boston blue clay (BBC). The excavations were supported by 27-m-deep floating diaphragm wall panels and five levels of preloaded cross-lot bracing. This paper compares the measured performance of the excavation support system with the Class A finite-element (FE) predictions prepared during the original design phase and with the results of Class C analyses using information obtained during construction. The numerical analyses used data from a special test program of laboratory and in situ tests at a nearby site. The analyses represent coupled consolidation within the soil mass and the anisotropic stress-strain-strength properties of BBC using the MIT-E3 soil model. The Class A analyses generally overestimate the lateral wall deflections and underestimate the measured strut loads, as preloading was not included in the original FE model. However, they provide remarkably consistent predictions of the measured soil deformations, including settlements, lateral spreading, and subgrade basal heave. The Class C analyses refine the stratigraphic section, in situ pore pressures, construction time frame, and strut preloads using the data available at the time of construction but make nominal changes in soil properties. With these limited changes, the Class C model is able to achieve excellent agreement with the measured data.
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Acknowledgments
The authors are grateful to the MBTA for supporting the original Class A analyses for Section CC07 of the South Piers Transitway Project. Parsons Brinckerhoff were the design engineers and were responsible for monitoring the performance of the excavations. The construction was carried out by JF White Contracting Company. The views and opinions expressed in this paper are those of the authors and are not those of the organizations or other individuals responsible for the completion of this project. Mary Ainsley (MBTA), Richard O’Brien (PB), and Youssef Hashash (now at UIUC) were instrumental in setting up the original study. The second author (G. C.) was partially supported by a scholarship through the Beca Presidente de la República de Chile for his Ph.D. studies at MIT. The authors would also like to thank Boonchai Ukritchon and Yixing Yuan, who performed the basal stability calculations, and Sherif Akl and Paul Bonnier, who integrated the MIT-E3 model in the PLAXIS code.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 141 • Issue 4 • April 2015
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Dec 28, 2013
Accepted: Oct 20, 2014
Published online: Dec 17, 2014
Published in print: Apr 1, 2015
Discussion open until: May 17, 2015
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