Location

St. Louis, Missouri

Session Start Date

6-1-1993

Abstract

A case history and analysis are presented of a 76-foot deep braced excavation in competent silt- and claystone formations. Soldier piles and lagging were supported by three levels of struts above three levels of tie-backs. During construction, measured strut loads exceeded design levels by up to 100 percent, and additional struts were installed in the upper portion of the excavation. Back analysis performed after construction indicated that large horizontal insitu stresses (Ko= 1) in the region had contributed to the overloading. It was also shown that the problem had been compounded by the practice of pre loading the struts upon installation. The analysis further indicated that for excavations in competent, rock-like materials, excess strut loads can be safely relieved by allowing small elastic deflections of the excavation walls to take place. A simple design scheme is suggested which would allow such deformations without adversely affecting the overall performance of the excavation support system.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Third Conference

Publisher

University of Missouri--Rolla

Publication Date

6-1-1993

Document Version

Final Version

Rights

© 1993 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Jun 1st, 12:00 AM

Performance of a Braced Excavation in Siltstone

St. Louis, Missouri

A case history and analysis are presented of a 76-foot deep braced excavation in competent silt- and claystone formations. Soldier piles and lagging were supported by three levels of struts above three levels of tie-backs. During construction, measured strut loads exceeded design levels by up to 100 percent, and additional struts were installed in the upper portion of the excavation. Back analysis performed after construction indicated that large horizontal insitu stresses (Ko= 1) in the region had contributed to the overloading. It was also shown that the problem had been compounded by the practice of pre loading the struts upon installation. The analysis further indicated that for excavations in competent, rock-like materials, excess strut loads can be safely relieved by allowing small elastic deflections of the excavation walls to take place. A simple design scheme is suggested which would allow such deformations without adversely affecting the overall performance of the excavation support system.