Summary

This report is produced in response to a series of incidents of ground instability and collapse that have occurred on recent tunnelling projects in suburban and city centre environments on which closed-face tunnelling machines were used. The purpose of this report is to examine the potential for ground instability or collapse when using closed face tunnelling machines, to investigate the efficacy of various ground investigation techniques in urban areas, and to recommend management and operational guidelines to further minimise the risk when tunnelling beneath highly developed urban areas.