Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

Recent advances in strain measurement using optical fibers provide new opportunities for monitoring the performance of geotechnical structures during and after construction. Brillouin optical time-domain reflectometry (BOTDR) is an innovative technique that allows measurement of full strain profiles using standard optical fibers. In this paper, two case studies illustrating the application of the distributed optical fiber strain sensors are presented. One is monitoring of an old masonry tunnel when a new tunnel was constructed nearby and the other is monitoring the behavior of secant piled walls for basement construction. Both sites are located in London. The advantages and limitations of this new sensor technology for monitoring geotechnical structures are discussed.

The paper describes the caisson construction problems encountered and the required modification necessary for a 55-story residential high-rise in Chicago’s near north side. Belled caissons were planned on a very thin hardpan bearing layer which was underlain by water bearing dense silt that extended to dolomite bedrock. Three filtered dewatering wells extending into the fractured rock surface were planned to reduce the hydrostatic pressure head within the silt to permit the belled construction. A complete collapse of the dense silt layer during the installation of the first dewatering well undermined the planned belled caisson foundation system. An additional subsurface investigation, a compaction grouting program and further in-situ pressuremeter testing was then performed. Subsequent modified performance predictions required the addition of selective micropile underpinning after completion of the planned system of grade beams and belled caisson installation. Settlement monitoring during building construction confirmed settlements within or less than the predicted settlement range.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Sixth Conference

Publisher

Missouri University of Science and Technology

Publication Date

8-11-2008

Document Version

Final Version

Rights

© 2008 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Unexpected Caisson Problems, Soil Structure Interaction Predictions and Required Ground Modification

Arlington, Virginia

Recent advances in strain measurement using optical fibers provide new opportunities for monitoring the performance of geotechnical structures during and after construction. Brillouin optical time-domain reflectometry (BOTDR) is an innovative technique that allows measurement of full strain profiles using standard optical fibers. In this paper, two case studies illustrating the application of the distributed optical fiber strain sensors are presented. One is monitoring of an old masonry tunnel when a new tunnel was constructed nearby and the other is monitoring the behavior of secant piled walls for basement construction. Both sites are located in London. The advantages and limitations of this new sensor technology for monitoring geotechnical structures are discussed.

The paper describes the caisson construction problems encountered and the required modification necessary for a 55-story residential high-rise in Chicago’s near north side. Belled caissons were planned on a very thin hardpan bearing layer which was underlain by water bearing dense silt that extended to dolomite bedrock. Three filtered dewatering wells extending into the fractured rock surface were planned to reduce the hydrostatic pressure head within the silt to permit the belled construction. A complete collapse of the dense silt layer during the installation of the first dewatering well undermined the planned belled caisson foundation system. An additional subsurface investigation, a compaction grouting program and further in-situ pressuremeter testing was then performed. Subsequent modified performance predictions required the addition of selective micropile underpinning after completion of the planned system of grade beams and belled caisson installation. Settlement monitoring during building construction confirmed settlements within or less than the predicted settlement range.