Safety Challenges in Metro Tunnel Construction While Using TBM/NATM for Tunnel Excavation

Metro tunnel construction is one of the most complex and hazardous forms of underground infrastructure development. Modern metro systems are generally excavated either by Tunnel Boring Machine (TBM) or by the New Austrian Tunnelling Method (NATM), depending upon the geological condition, tunnel geometry, urban constraints, and project economics. Although both methods improve construction efficiency, they introduce numerous safety challenges related to geology, machinery, occupational health, structural instability, and environmental impacts. The risks are more severe in metro projects because tunnels are usually excavated beneath densely populated urban areas where failure can affect workers, nearby structures, utilities, and public safety. This paper examines the principal safety challenges associated with TBM and NATM tunnel excavation in metro construction. It identifies all possible hazards, compares the risk profile of both methods, discusses accident mechanisms, and proposes preventive and mitigation measures.