Challenges and Solutions for large scale Tunnelling in Urban Environment
Tunnelling in soft ground in urban environment is a challenging task which requires comprehensive design solutions tailored to the particular ground and boundary conditions. This paper illustrates some interesting design solutions for tunnels with large cross-section below existing railway line and freeway tunnels below major freeway - both in Vienna in stiff clay and dense sands. Special measures as de-watering from surface, jet-grouting and pipe roofs were applied. Other challenging tunnel drives were designed for subway tunnels for the project Metro 4 in Budapest in stiff clay and dense sands. The most difficult tunnels are located below the Danube in fault zones and others below existing buildings. Special measures as freezing and de-watering were designed. In Stockholm the mixed face conditions between hard rock and loose sand was a challenging task for tunnel design and construction. For safe tunnelling jet-grouting canopy turned out to be suitable. All cases confirmed the experience that for tunnelling in urban environment the knowledge of the ground is most important. Any cost for site investigations can save major cost during later construction. .