Abstract: The Second Jiaozhou Bay subsea tunnel is featured by super length, super size, super depth, complicated geological conditions, difficult ventilation and smoke extraction conditions, difficult evacuation and rescue conditions, complicated connection to the road network on both coasts, and restrictions on construction conditions. In this study, the authors study on 〖HJ5mm〗key issues of the superlong subsea tunnel, including the location, construction method, overburden, arrangement in tunnel, ventilation and smoke extraction, evacuation and rescue, in order to construct the Second Jiaozhou Bay subsea tunnel in a scientific, safe and economic way. The following main findings are concluded: (1) The concept of selecting the tunnel alignment based on the geological conditions shall be emphasized in the general design of the superlong subsea tunnel, which is key to reducing the construction and operation risks, controlling the investment and guaranteeing the construction period. (2) In the general design of the superlong subsea tunnel, it is important to compare different construction methods, select appropriate construction methods for different sections of the subseal tunnel and determine the reasonable overburden according to the specific geological and construction environment conditions. (3) The subsea section of the Second Jiaozhou Bay subsea tunnel consists of twin main tunnel tubes and one service tunnel tube. The air passage is set at the top area of the subsea section of the main tunnel tubes, the innovative 2.5section ventilation plan is put forward, and the service tunnel is also used as the fresh air channel, which solves the ventilation problem of the super-long subsea tunnel. (4) A management center is set up at each portal of the tunnel, an emergency management station is set up at the portal of the service tunnel. Moreover, a complete evacuation and rescue system, which consists of the service tunnel, the pedestrian/vehicle cross passages, and the evacuation stairs and the longitudinal evacuation channel in the lower part of the shieldbored section, is arranged. In this way, the operation safety of the superlong subsea tunnel is guaranteed.

Key words: subsea tunnel, general design, selecting tunnel alignment according to geological conditions, service tunnel, construction method selection, ventilation and disaster prevention