Abstract: Presently, owing to the demand of construction scale and design function, many superlargediameter shields have been widely used in tunnel engineering in railways, highways, urban rail transits, underground utility tunnels, and other areas. In this paper, a preliminary statistic on the superlargediameter (more than 15.5 m) shield tunnel projects around the world is presented. The main risks of largediameter shield tunneling, such as main bearing damage and failure, segment floating after segment assembly and removal from shield tail, cutter wear increasing with shield diameter, mud cake bonding on cutterhead, hysteretic discharge of muck, and cutterhead heating, are summarized. Additionally, related countermeasures are provided based on case analysis. Moreover, suggestions are put forward regarding main bearing seal of earth pressure balance shield and slurry shield, floating risk after segment assembly and removal of shield tail, cutterhead selection, mud cake bonding and hysteretic discharge of muck, preexploration of complex geology, and blasting and grouting consolidation of sea bedrock.

Key words: largediameter shield, main bearing seal; segment upfloating, cutter wear, mud cake bonding; hysteretic discharge of muck, conventional cutterhead, cutterhead with atmospheric pressure, geological preexploration; bedrock blasting, grouting consolidation