ABSTRACT
The risk-level can be reduced by choosing a tunnel boring machine (TBM) with face support, but the reduction may not always achieve an acceptable level of risk. It is believed that the correct selection of the construction method shall constitute a primary measure for reducing the identified initial-risk levels. The main drive is one of the most important mechanical parts of a TBM. In Closed-Face Machines the main bearing can potentially be polluted by pressurized slurry contained in the plenum. The special requirements for a city machine are related to: excavation process (including maintenance and muck handling), face-support-pressure control facilities, parameters cross-control system, probe-drilling ahead of the face, ground treatment, guidance, and safety of workers. The lower part of the bulkhead in the front shield of an earth pressure balance shield must be equipped with a safety gate, which can be closed when the screw conveyor is retracted for maintenance.
