Abstract: To further improve the waterproof capability of underwater tunnels with superdeep water and various geological conditions, comparison is made between immersed and shield tunnels based on existing structures and construction technologies. A new type of watershield machine and relevant tunneling technology (guidedshield tunneling) are proposed based on basic technical element extraction and innovation methods. For the guidedshieldtunneling method, guided tubes are laid in advance as waterproof structures. Subsequently, the water shield tunnels in the tubes to drain, thus creating a dry environment to conduct segment erection. Finally, pressurized grouting is employed to fill the gaps, thus integrating the guided tubes and tunnel segments to form the main tunnel structures. This method has many advantages, including low requirements on ground conditions, adaptability to various waterhead pressures, and good waterproof performance. Thus, this method improves assembly construction rate and the standardization level of components, making it a potential mainstream technique in underwater tunneling. The comparative results of economic indexes show that: (1) the cost of waterproof structures requires a greater portion of the total cost of the guidedshieldtunneling method than that in the shield or immersed tunneling method; (2) the cost of soil excavation in the guidedshield tunneling method is much less than that in the shield method; (3) the cost of concrete and main structures in the guidedshield tunneling method is much less than that in the immersed tunneling method; thus, the guidedshield tunneling method has good economic benefits.

Key words: underwater tunnel, guiding tube, water shield, tunneling method, tunnel engineering