Location

New York, New York

Session Start Date

4-13-2004

Session End Date

4-17-2004

Abstract

The Seattle Central Library project, which replaced the existing downtown library, consists of a twelve-story building with several below-grade levels. The excavation encompassed an entire city block and had plan dimensions of approximately 250 feet by 240 feet. The original excavation depth was up to 53 feet in height. The excavation was made in highly overconsolidated Seattle silts and clays (Lawton Clay). The Lawton Clay has been documented to exhibit expansive behavior along planes of weakness associated with stress relief upon excavation. The original excavation was designed to be supported using a tieback soldier pile wall, typical of shoring systems retaining the Lawton Clay. A soil nail shoring wall design was submitted, and subsequently installed, as part of a design-build alternative. The soil nail shoring wall system consisted of temporary, top-down soil nail walls that utilized portions of the concrete basement walls of the existing library. Vertical elements and shotcrete facing were constructed in areas where the excavation extended beyond or below the existing basement walls. Soil nails were installed using self-boring grout-injected anchors consisting of hollow bars with sacrificial drill bits. Displacement of the soil nail shoring walls was predicted to be less than 1 inch by the designer. The actual wall movements for three sides of the excavation were as predicted. However, the east wall on the uphill side of the excavation experienced 4 inches of lateral movement and over 2.5 inches of vertical movement, causing damage to the adjacent street and necessitating extensive design modifications during construction. In addition, the excavation depth was reduced to 47 feet because of significant movement occurring below the excavation. This paper describes the construction and observed behavior of the east wall and the applicability of soil nail walls in the Lawton Clay deposit.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fifth Conference

Publisher

University of Missouri--Rolla

Publication Date

4-13-2004

Document Version

Final Version

Rights

© 2004 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 13th, 12:00 AM Apr 17th, 12:00 AM

Observations and Performance of a Soil Nail Shoring Wall in Seattle Silts and Clays

New York, New York

The Seattle Central Library project, which replaced the existing downtown library, consists of a twelve-story building with several below-grade levels. The excavation encompassed an entire city block and had plan dimensions of approximately 250 feet by 240 feet. The original excavation depth was up to 53 feet in height. The excavation was made in highly overconsolidated Seattle silts and clays (Lawton Clay). The Lawton Clay has been documented to exhibit expansive behavior along planes of weakness associated with stress relief upon excavation. The original excavation was designed to be supported using a tieback soldier pile wall, typical of shoring systems retaining the Lawton Clay. A soil nail shoring wall design was submitted, and subsequently installed, as part of a design-build alternative. The soil nail shoring wall system consisted of temporary, top-down soil nail walls that utilized portions of the concrete basement walls of the existing library. Vertical elements and shotcrete facing were constructed in areas where the excavation extended beyond or below the existing basement walls. Soil nails were installed using self-boring grout-injected anchors consisting of hollow bars with sacrificial drill bits. Displacement of the soil nail shoring walls was predicted to be less than 1 inch by the designer. The actual wall movements for three sides of the excavation were as predicted. However, the east wall on the uphill side of the excavation experienced 4 inches of lateral movement and over 2.5 inches of vertical movement, causing damage to the adjacent street and necessitating extensive design modifications during construction. In addition, the excavation depth was reduced to 47 feet because of significant movement occurring below the excavation. This paper describes the construction and observed behavior of the east wall and the applicability of soil nail walls in the Lawton Clay deposit.