Abstract
By analyzing the field data from nine metro-station pits with aspect ratios (AR) of pit length to width of 6.6–19.4 in Shanghai soft clay, this paper investigates the potential corner effects (i.e., the retaining walls near pit corners have stronger capabilities to resist deformation than those distant away as a product of spatial arching effects across the pit corners) of long and narrow multipropped metro station excavations. Contrary to the two-dimensional (2D) plane-strain assumption widely adopted in practice for analysis of a metro station excavation (i.e., deformations of the pit in which the displacements of all points along the longitudinal sides are assumed to be parallel to a given plane in the transverse direction and the values of these displacements do not depend on the distance perpendicular to the plane), seven out of the nine metro station pits exhibited apparent corner effects and only two showed plane-strain conditions. Because of the stiffening effects from the pit corners, the minimum wall deflections occurred near the pit corners and the maximum occurred near the middle span of the pits. The development of the maximum wall deflections along the longitudinal sides of the pits, which were normalized by the final excavation depths, can be bounded by two liner curves. Because of their narrow widths, the observed corner effects of the metro stations were less pronounced than that of a rectangular excavation with an AR of about 2.0. Distinctly different from the findings in literature for regular rectangular excavations with AR of 1.0–2.0, the variation of either the pit length-to-depth ratio or the pit length-to-width ratio hardly affected the corner effects of metro station pits. The derived graphical solutions accounting for the influence of pit lengths on corner stiffening effects can be used as references for future design and construction of a long and narrow multipropped pit in soft clays. The monitoring data regarding the adjacent building settlements demonstrate that the mobilized corner stiffening effects during excavation were helpful in constraining the ground deformation and protecting the structures or facilities in the proximity.
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Acknowledgments
The financial supports from the Innovation Program of Shanghai Municipal Education Commission (No. 13ZZ027) and the Program for Changjiang Scholar and Innovative Research Team in University (PCSIRT, IRT1029) are gratefully acknowledged. The great comments and suggestions from the three anonymous reviewers and the Editor are sincerely appreciated.
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Journal of Performance of Constructed Facilities
Volume 28 • Issue 4 • August 2014
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© 2014 American Society of Civil Engineers.
History
Received: Nov 27, 2012
Accepted: May 21, 2013
Published online: May 23, 2013
Published in print: Aug 1, 2014
Discussion open until: Oct 23, 2014
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