Abstract:  Vacuum tube transportation has a small cross-section, light structure, and good integration, it should be laid on seabed or elevated, and has advantages such as low construction cost, minimal environmental impact, safe, stable, and reliable. Based on the analysis of terrain and landforms, four alternative route schemes are proposed as follows: (1) Xuwen Jiaowei (N20°13′39″, E109°55′39″)-Chengmai Qiaotou (N19°59′19″, E109°56′15″) (West line), with a sea surface distance of 26.5 km and a maximum depth of 47 m, and a relatively gentle seabed terrain. (2) Hai′an Nanshan (N20°13′48″, E110°07′33″)-Haikou Xinhai (N20°03′42″, E110°09′40″) (M1a line), with a sea surface distance of 19 km and a maximum depth of 84 m. (3) Hai′an Qing′an (N20°14′41″, E110°16′56″)Haikou Haidian (N20°05′05″, E110°20′44″) (M2b line), with a sea surface distance of 20 km and a maximum depth of 80 m. (4) Longtang Xiatang (N20°19′47″, E110°26′15″)-Haikou Puqian (N20°06′34″, E110°35′46″) (East line), with a sea surface distance of 30 km and a maximum depth of 47 m, the seabed terrain is relatively gentle. A comparative analysis is conducted on the M1b and M2a lines, and the M1a line is recommended as the priority. Preliminary analysis is conducted on the seawater depth, longitudinal section, longitudinal slope, and submarine tube alignment of each route. The geodetic coordinates of the endpoints of each line are estimated, and the polar coordinates of longitude and latitude of 0.50 ″ is capable of meeting the endpoint positioning accuracy requirements for line scheme analysis and preliminary feasibility study. When the diameter of tube is relatively large (≈5 m) and the speed of vehicles inside the tube is low, vacuum pumping is not necessary, it can be serviced as a common submarine tube, which is also one of the options for Qiongzhou strait sea-crossing channel.

Key words: Qiongzhou strait, sea-crossing channel, seabed vacuum tube transport, route scheme