Jubilee line extension project

Jubilee line extension project
The construction of London Bridge Station below sensitive structures

ÖIAZ 4/1997

Österreichische Ingenieur- und Architekten-Zeitschrift (ÖIAZ), 142 Jg.,Heft 4/1997

The Project
London Underground Ltd. are currently constructing an extension of the Jubilee Line that will commence at Green Park and extend to West Ham. The total length of the route is 15.4 km with 11.4 km underground. Eleven new station complexes are under construction eight of which under ground. All main tunnels at London Bridge Station (Contract 104) were constructed following the principles of the New Austrian Tunneling Method (NATM).

The new London Bridge Station complex, which is close to the existing London Bridge Railway Station, includes the development of Running Tunnels (22 m2), two Platform Tunnels (60 m2), a Central Concourse Tunnel (110 M2), Escalator Tunnels (57 m2), Interlocking Machine Chamber (60 m2) and two Ventilation Tunnels (60 m2). Total span of the station complex is approximately 30 m.

Building and Subsurface Structures 
Contract 104 is the most complex scheme of the Jubilee Line Extension Project with regards to its location beneath the vast brick structure of the existing London Bridge Railway Station, other historic listed and sensitive surface structures, as well as Borrow High Street, which is a major traffic corridor under
by countless service ducts for water, gas and electricity. Furthermore, live SGI-lined tunnels of the Northern Line had to be undermined and new tunnels constructed in close vicinity to these tunnels.

The Target
Due to the above conditions, very stringent limits to surface settlements and ground deflections have been imposed on the contract by British Rail, as well as service operators and the property owners. Apart from developing an excavation and support method minimizing the ground displacement, a settlement reducing measure, that is Compensation Grouting, had to be activated, before the maximum value had been reached to avoid damage of the surface structure. The maximum value for the surface settlement adjacent to the sensitive buildings has been stipulated to be 25 mm, whilst the maximum angular distortion at these buildings was not allowed to exceed 1/1000.

Results Achieved
The surface settlement above platform tunnels was limited to the required value by Compensation Grouting. Areas not treated with Compensation Grouting settled by up to 40 mm. Existing SGI-lined tunnels deflected horizontally by 4 mm, vertically by 8 mm and settled by maximum 15 mm.

The Involvement
The Dr. G. Sauer Company Ltd. is responsible for the design of the excavation method, the initial and final support of all NATM works. The Dr. G. Sauer Company Ltd. also provided key site personnel to supervise the NATM construction, being the technical consultant for the contractor Costain Taylor Woodrow Joint Venture.