ABSTRACT
Tunneling is an experienced based profession and tunneling practitioners can learn a significant amount of information from previous projects, particularly those tunnel projects associated with challenges and problems where solutions were implemented for successful completion. This chapter presents lessons learned from several historical tunnel projects. The discussion of these past projects is intended to highlight some important lessons learned for future tunnel projects. Tunnel support designs for shallow tunnels in urban areas where deep weathering is present and uncertainty exists should be based on a conservative approach to limit excavation advance and require high capacity passive support. The design and construction of large tunnels in very weak rock conditions should be based on an appropriately conservative approach for excavation sequencing with an ongoing performance based evaluation of tunnel stability based on instrumentation data reviewed on a regular basis by well qualified and experienced tunnel engineers.
