Modeling of Pipe Arch Canopies in Shallow Soft Ground Tunnels Constructed by Sequential Excavation Methods

Synopsis:

The New Austrian Tunneling Method (NATM), also referred as Sequential Excavation Method (SEM), has found application in soft ground in urban tunneling in the late 60’s and has since then enjoyed a broad, international utilization in both rural and urban settings. One key element, which enlarged the adaptability of NATM tunneling in soft ground and low overburden environments enormously in the recent decade, is the application of pipe arch canopies used as a systematic pre-support measure. However, the effective numerical modeling of pipe arch canopies is still a challenge. Very often models do not fully utilize the positive effect on the surface settlements in particular when using two-dimensional techniques and three dimensional models are required to approximate the pre-support benefits and provide guidance on the design for the pipe arch canopies.

This paper demonstrates opportunities how to model pipe arch canopies and how to take credit of the positive settlement controlling effects in Finite Element (FE) modeling. Project examples will be discussed and include the Tysons Corner Tunnels, Washington D.C. and the Fort Canning Tunnel, in Singapore. This article will summarize the findings and provide guidance on how to generally adapt the approach to other projects.

Modeling of Pipe Arch Canopies in Shallow Soft Ground Tunnels Constructed by Sequential Excavation Methods
Proceedings 2nd International Conference on Computational Methods in Tunnelling
September 9-11, 2009
Ruhr University, Bochum, Germany