Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

One of the largest development projects in the City of Beirut involved the excavation of an area of 14,000m2 down to a depth of 30m below street level. The site is in an urban area and bound by major traffic arteries and a multi-storey office building. The shoring approach adopted for the excavation boundary walls consisted of a hybrid flexible system with multiple rows of pre-stressed anchors, followed by rows of passive nails at varying spacings and lengths. A reinforced shotcrete facing was provided across the full depth of the excavation. Upon reaching the final excavation grades across the whole site, significant movements were recorded along one of the site boundaries (approximately 120m long) adjacent to the main traffic artery. These deformations at the face were accompanied by longitudinal cracks up to 20m away from the excavation boundary along the main road, with differential downward movements on the order of 5 to 10 centimeters. The pattern of deformation and location of cracks suggested an impending deep seated failure. This resulted in the closure of all adjacent roads to traffic and emergency backfilling measures to shore the compromised wall. At this stage third party forensic failure analyses were initiated in which we were involved. In this paper, the background related to site-specific sub-surface characterization efforts, along with design choices and options adopted are be presented and discussed. Post-movement analyses and monitoring results are used to identify the reasons behind the failure. Finally, remedial measures implemented are described and discussed in detail along with lessons learned.

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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Failure of a Hybrid Flexible Shoring System for a 30m Excavation: Exploration of Causes and Remedial Measures

Arlington, Virginia

One of the largest development projects in the City of Beirut involved the excavation of an area of 14,000m2 down to a depth of 30m below street level. The site is in an urban area and bound by major traffic arteries and a multi-storey office building. The shoring approach adopted for the excavation boundary walls consisted of a hybrid flexible system with multiple rows of pre-stressed anchors, followed by rows of passive nails at varying spacings and lengths. A reinforced shotcrete facing was provided across the full depth of the excavation. Upon reaching the final excavation grades across the whole site, significant movements were recorded along one of the site boundaries (approximately 120m long) adjacent to the main traffic artery. These deformations at the face were accompanied by longitudinal cracks up to 20m away from the excavation boundary along the main road, with differential downward movements on the order of 5 to 10 centimeters. The pattern of deformation and location of cracks suggested an impending deep seated failure. This resulted in the closure of all adjacent roads to traffic and emergency backfilling measures to shore the compromised wall. At this stage third party forensic failure analyses were initiated in which we were involved. In this paper, the background related to site-specific sub-surface characterization efforts, along with design choices and options adopted are be presented and discussed. Post-movement analyses and monitoring results are used to identify the reasons behind the failure. Finally, remedial measures implemented are described and discussed in detail along with lessons learned.