Abstract: Asymmetricallypressure in subsea tunnel often causes rib spalling, water gushing and primary support deformation. Based on the crosssea passage project from Xiamen island to Xiang ′an in Xiamen metro line 3, measures of geological prediction, stratum reinforcement, tunnel excavation and support and risk management are analyzed. The results show that: (1)Due to the location of subsea tunnel, in addition to the construction measures of advanced geological prediction, advanced formation water plugging and reinforcement, and prevention and control of sudden gushing, a set of strict emergency countermeasures including rescue, disaster relief and prevention of sudden accidents should be taken to guarantee absolute personnel and equipment safety. (2) In construction, formation reinforcement and seepage control should be carried out in time by advanced prereinforcement grouting according to the variations of geological and hydrogeological conditions, and it should be fully prepared at all times for possible emergency. （3) In broken, unsymmetricallypressured and unstable stratum, the primary support, taking steel arch as the main supporting parameter, has the advantage of high rigidity, high strength and being adaptive to the stress of surrounding rock after tunnel excavation, thus it can effectively control the initial deformation after excavation in weak surrounding rock tunnel. (4) In excavation, a certain amount of backfill slag and an emergency operation platform should be prepared so that quick rescue and efficient work can be done with low cost in emergency event.

Key words:

subsea tunnel, weathered sac, asymmetricallypressured section, high water pressure, formation reinforcement, risk control, construction technique