Hard rock TBM tunneling in challenging ground: Developments and lessons learned from the field

TBM tunneling is an ever-increasing challenge for underground construction, and with each new tunnel bored there are unknown elements when boring through the earth. The most extensive Geotechnical Baseline Reports can miss fault lines, water inflows, squeezing ground, rock bursting, and other types of extreme conditions. This paper will draw on the considerable experience within Robbins to analyze successful methods of dealing with the most challenging conditions encountered, with a particular focus on fractured and faulted ground, mixed face tunneling, and tunneling in karst or water-bearing conditions. It will discuss new methods, including Dual Mode or “Crossover” type machines, which can increase the efficiency of excavation in such conditions.