Alternative Title

Paper No. 6.09

Location

St. Louis, Missouri

Session Start Date

3-8-1998

Session End Date

3-15-1998

Abstract

Two types of excavation support system were used on the southern approach of the Ted Williams Tunnel; part of Boston’s Central Artery/Tunnel Project. Construction commenced in 1992 and was completed in 1995.

The cut and cover tunnel was constructed to accommodate a four-lane highway, and associated structures. The excavation was mainly in soft marine clays, known locally as the Boston Blue Clay. The main excavation support system consisted of tied-back interlocking steel sheeting. The proximity of large commercial buildings to the excavation necessitated a stiffer support system to reduce the magnitude of ground deformation at the building locations. A 3-feet thick tied-back tremie concrete slurry wall was constructed. Both support systems were heavily instrumented. Instruments were installed behind the walls as well as within the excavation to monitor the ground water levels, ground and excavation support wall movements, and building deformations. The instruments consisted of inclinometers, heave gages, probe extensometers, strain gages, piezometers, observation wells, and building and ground deformation monitoring points.

Ground and building deformations occurred as a result of dewatering and excavation. Mitigating measures included staged excavations and groundwater drawdown control.

This paper presents an overview of the ground conditions, the instrumentation program, the construction, and the instrumentation data to compare the two excavation support systems.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Fourth Conference

Publisher

University of Missouri--Rolla

Publication Date

3-8-1998

Document Version

Final Version

Rights

© 1998 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Comparison of Two Excavation Support Systems in Clay: Central Artery Tunnel, Boston, Massachusetts, USA

St. Louis, Missouri

Two types of excavation support system were used on the southern approach of the Ted Williams Tunnel; part of Boston’s Central Artery/Tunnel Project. Construction commenced in 1992 and was completed in 1995.

The cut and cover tunnel was constructed to accommodate a four-lane highway, and associated structures. The excavation was mainly in soft marine clays, known locally as the Boston Blue Clay. The main excavation support system consisted of tied-back interlocking steel sheeting. The proximity of large commercial buildings to the excavation necessitated a stiffer support system to reduce the magnitude of ground deformation at the building locations. A 3-feet thick tied-back tremie concrete slurry wall was constructed. Both support systems were heavily instrumented. Instruments were installed behind the walls as well as within the excavation to monitor the ground water levels, ground and excavation support wall movements, and building deformations. The instruments consisted of inclinometers, heave gages, probe extensometers, strain gages, piezometers, observation wells, and building and ground deformation monitoring points.

Ground and building deformations occurred as a result of dewatering and excavation. Mitigating measures included staged excavations and groundwater drawdown control.

This paper presents an overview of the ground conditions, the instrumentation program, the construction, and the instrumentation data to compare the two excavation support systems.