• Railroad / Transit Tunnels
  • Tunnel Rehabilitation
  • Waterproofing
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Green Park Station

London Underground Ltd. (LUL)

The Step-Free Access (SFA) project’s main goal is to provide step-free access from street level to all operational platforms via the ticket hall and between platforms for interchange purposes.

Modeling and Design Services for lift shaft and lift lobby tunnel stub using SCL / NATM:

Gall Zeidler Consultants provided design and computer modeling services for a shaft and tunnel stub to be constructed using Sprayed Concrete Lining / New Austrian Tunneling Method (SCL / NATM). These structures serve as an elevator shaft and the elevator lobby, respectively.

The shaft and tunnel stub will be constructed entirely in London Clay. The initial shaft and tunnel stub support consists of a reinforced shotcrete lining. Excavation followed the principles of SCL / NATM. A PVC membrane-based waterproofing system as well as shotcrete and cast-in-place concrete linings were installed for permanent support.


London, United Kingdom


2008 – 2009


Shaft and Tunnel Stub


Tunnel Stub – 15.0 feet (4.6 meters)


Oval Shaft Diameter 29.9 / 31.5 high (9.1 / 9.6 meters) Axis Length – 91.0 feet (27.7 meters) Depth
Tunnel Stub – 28.5 feet (8.7 meters) Width, 42 feet (12.8 meters) Heigh


Man-Placed Fill, London Clay; Groundwater Table Approximately 9 – 12 feet (3 – 4 meters) Below Surface


Approximately US $30 Million


Donaldson Associates


London Underground Ltd. (LUL)