Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

The National Institutes of Health (N.I.H.) Utility Tunnel development consists of an underground concrete utility vault (measuring approximately 44 ft long by 25 to 32 ft wide) and tunnel (measuring about 30 ft long by 16 ft wide). The overall structure extends 28 feet below existing grade and 16 feet below the existing tunnel located on the National Institutes of Health Campus in Bethesda, Maryland. The proposed tunnel/vault structure is supported by a 2.5 foot thick mat foundation. The top 24 feet of soil consists primarily of fill material, a mixture of silty sand and sandy silt with an underlying layer of disintegrated Schist rock. The proposed structure requires temporary sheeting and shoring that would both support the existing mix-use tunnel and allow for the safe excavation and construction of the proposed underground structure. A conventional needle beam shoring system was ruled out due to the lack of space, the need to eliminate unnecessary tunneling, and to accelerate overall project schedule. A large scale utility hanging system was conjured, consisting of nine drilled solder piles and 27 drilled bracket piles. Each pile was drilled from existing grades prior to the start of excavation. As the existing cast-in-place utility tunnel structure was uncovered, brackets were installed on the surrounding bracket piles while the surface was prepared to receive the proposed epoxy rods. The overhead utility support system utilized drilled epoxy Williams’ threaded bars to transfer the loads into supporting double c-channel walers and strong-back cross members. Each strong-back was designed to compensate for the calculated deflection of the tunnel once the below-structure excavation operations began. Distribution wales and header beams were utilized along the length of the existing utility tunnel and connected at the surrounding bracket piles. Upon successfully jacking the epoxy rods, the tunnel loading was directly transferred into the underlying bracket piles and distributed into soils below the proposed structure. Excavation began beneath the existing tunnel upon the final approval of the jacking data for the epoxy rods and all bracket welds were verified. Beneath the structure, each bay between bracket piles was lagged while the opposite site was sloped to create a tunnel for the underpinning access. Excavation commenced to the proposed subgrade at the completion of the underpinning piers. The remaining proposed utility vault portion of the project was completed upon the installation of an external waler and internal strut bracing system. Each waler and internal strut was specifically designed to eliminate the need for excessive patching with the newly poured cast-in-place below-grade walls. Monitoring strips and points were installed along the tops of each bracket pile and along the roof of the existing tunnel structure. Crack monitors were installed at an existing expansion joint located directly in the center of the supported tunnel system. At the overall completion of the project, there were no signs of settlement within existing utility tunnel as well as notable movement of solder and bracket piles.

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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Aug 11th, 12:00 AM Aug 16th, 12:00 AM

Excavation and Shoring Support for the National Institutes of Health East Redundancy Loop Project at Building 10 on N.I.H. Campus in Bethesda, Maryland

Arlington, Virginia

The National Institutes of Health (N.I.H.) Utility Tunnel development consists of an underground concrete utility vault (measuring approximately 44 ft long by 25 to 32 ft wide) and tunnel (measuring about 30 ft long by 16 ft wide). The overall structure extends 28 feet below existing grade and 16 feet below the existing tunnel located on the National Institutes of Health Campus in Bethesda, Maryland. The proposed tunnel/vault structure is supported by a 2.5 foot thick mat foundation. The top 24 feet of soil consists primarily of fill material, a mixture of silty sand and sandy silt with an underlying layer of disintegrated Schist rock. The proposed structure requires temporary sheeting and shoring that would both support the existing mix-use tunnel and allow for the safe excavation and construction of the proposed underground structure. A conventional needle beam shoring system was ruled out due to the lack of space, the need to eliminate unnecessary tunneling, and to accelerate overall project schedule. A large scale utility hanging system was conjured, consisting of nine drilled solder piles and 27 drilled bracket piles. Each pile was drilled from existing grades prior to the start of excavation. As the existing cast-in-place utility tunnel structure was uncovered, brackets were installed on the surrounding bracket piles while the surface was prepared to receive the proposed epoxy rods. The overhead utility support system utilized drilled epoxy Williams’ threaded bars to transfer the loads into supporting double c-channel walers and strong-back cross members. Each strong-back was designed to compensate for the calculated deflection of the tunnel once the below-structure excavation operations began. Distribution wales and header beams were utilized along the length of the existing utility tunnel and connected at the surrounding bracket piles. Upon successfully jacking the epoxy rods, the tunnel loading was directly transferred into the underlying bracket piles and distributed into soils below the proposed structure. Excavation began beneath the existing tunnel upon the final approval of the jacking data for the epoxy rods and all bracket welds were verified. Beneath the structure, each bay between bracket piles was lagged while the opposite site was sloped to create a tunnel for the underpinning access. Excavation commenced to the proposed subgrade at the completion of the underpinning piers. The remaining proposed utility vault portion of the project was completed upon the installation of an external waler and internal strut bracing system. Each waler and internal strut was specifically designed to eliminate the need for excessive patching with the newly poured cast-in-place below-grade walls. Monitoring strips and points were installed along the tops of each bracket pile and along the roof of the existing tunnel structure. Crack monitors were installed at an existing expansion joint located directly in the center of the supported tunnel system. At the overall completion of the project, there were no signs of settlement within existing utility tunnel as well as notable movement of solder and bracket piles.