The mainline running tunnels for Legacy Way comprise two tunnel boring machine (TBM) driven tunnels. Both TBM drives commenced at the Launch Portal adjacent the Mt Coot-tha Road. Excessive surface settlement arising from tunnelling would have had a significant impact to the road infrastructure. The geological structure above the tunnel springline is a mixture of fill, residual soil and weak rock. Given the combination of low ground cover and weak ground materials, along with the use of an open face TBM, an oversize pipe umbrella system has been installed above the tunnels. This pipe umbrella system is similar to that commonly adopted in conventional mined excavation support in soft ground except that the steel pipes are substantially larger in geometry and filled with concrete. It is acknowledged that similar systems with oversize pipe umbrella have been adopted elsewhere in the world in other projects. These systems often comprise of a full arch formed by conjoining oversize steel pipes (in contact only). By aligning the pipes in contact, the arching behaviour of the steel pipe would have been enhanced. However, this poses a degree of construction difficulty due to excavation and installation method of the pipes. The Legacy Way pipe umbrella system only consists of a partial arch at the tunnel crown and each pipe is spaced approximately 1200 mm apart with 900 mm diameter pipe, leaving a gap of approximately 300 mm between pipes. A reinforced concrete portal block was used to support the exposed ends of the pipes.This paper reviews the design analysis, the recorded deflections from the pipe umbrellas and surface monitoring during TBM launch and revisits the analysis using the newly available RS3 program, from Rocscience for 3D analysis of geotechnical structures.CITATION:Norbert, M and O'Connor, D, 2014._x000D_
Starting the journey - launching of the Legacy Way open face tunnel boring machines in mixed face ground conditions, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 307-314 (The Australasian Institute of Mining and Metallurgy: Melbourne).