Predicted and encountered deformations

• Published in: Tunnels & Tunnelling International no. AOU; pp. 51 - 54
• Main Author: FEIERSINGER, Andreas
• Format: Journal Article Trade Publication Article
• Language: English
• Published: Sidcup Progressive Media Group 01-08-2011; Compelo
• Subjects: Applied sciences; Buildings; Buildings. Public works; Computation methods. Tables. Charts; Concrete; Construction; Construction contracts; Deformation; Dimensional analysis; Elevators & escalators; Exact sciences and technology; Finite element analysis; Public facilities (municipal, law court, etc.); Shear strength; Structural analysis. Stresses; Types of buildings; United Kingdom; Europe; United Kingdom > UK; England; London England; Design; Deformation measurement; Finite element method; Construction works; Improvement; Subway station; Forecast model; Computing method; Comparative study; Monitoring
• ISSN: 1369-3999

The shaft and tunnel works involved the design and construction of a SCL ellipsoid shaft, stub tunnel and stair passage tunnel (see Figure 1 , above). The shaft will house two 19-person Machine Room Less lifts which will take Tube passengers from the new subsurface ticket hall extension to the Victoria line and the Piccadilly and Jubilee line interchange passageway. The stub tunnel will provide lobby areas to each lift landing and connection to existing circulation and passageway assets. The ellipsoid shaft consisted of a smaller upper part, which is belled out for the larger lower part. The upper part extends to approximately 1 0m below the base of the new ticket hall slab with a major axis of approximately 8.6m and a minor axis of 5.6m for excavation. The upper shaft followed a 2m transition before the larger lower part began. This cross section extended uniformly to the shaft bottom at approximately 27m below the base of the ticket hall slab. The excavated major and minor axis lengths of the lower shaft were approximately 10m and 6.2m respectively. During the design the impact of construction onto the existing Victoria line escalator barrel was a major issue. Containing three escalators (numbers four, five and six), the barrel connects the Victoria line platforms to the existing ticket hall with escalator number four being closest to the shaft and stub tunnel excavation. Hence, escalator number four was anticipated to suffer most from deformations and was put on hydraulic jacks to counteract vertical deformations. In the Tube station itself the Victoria line platform tunnels, cross passages, the Victoria line escalator barrel, upper and lower escalator machine chambers and the ticket hall were thoroughly monitored. The scheme comprised of 153 prisms, 50 tiltmeters, 88 electrolevels, 37 tape extensometer points and 32 track sensors. All prisms were automatically read from five robotic total stations on an hourly basis. Tiltmeters and electrolevels were read hourly from a data logger. Convergence measurements were performed weekly in the Victoria line cross passages and running tunnels using tape extensometers. Approximately 20m of all four rails located in the Victoria line platform tunnels were monitored with track sensors providing hourly readings.