The Shalao section of Qingdao Metro Line 4 runs through, which is the first ultra-shallow buried subway shield section that crosses the tidal river under seawater in China

On July 21, with the "Dongfang No.2" shield tunneling machine breaking out of the rock at Laoshan No.6 Middle Station, the shield tunneling on the left line between Shazikou Station and Laoshan No.6 Middle Station of Qingdao Metro Line 4 received the tunneling smoothly, and the Shilao section of Line 4 was successfully completed.

The single line in this area is about 1115 meters long, the minimum curve radius of the plane is 450 meters, and the buried depth of the vault is 7.0-17.2 meters. Along the line, there are multiple first-level risk sources such as the south Jiushui River, residential buildings, the soft and hard strata above and below, etc., which are the key and difficult technical projects of the whole line. The right line of this area was completed on May 25.

Three risk sources to the section construction brings great danger, China Railway 24th Bureau project construction director Li Xingjie compared the difficulty of construction to "dancing on the edge of a knife". The tunnel diagonally crosses the Nanjiushui River for about 101 meters, with a buried depth of about 7 meters and a distance of 200 meters from the estuary. The channel water level is the deepest of about 2 meters at high tide. The groundwater is hydro-connected with the sea water, and the tides rise and fall twice a day. During the construction, the section was steadily advanced by means of tunneling at different speeds according to the tide table, synchronously injecting new material auxiliary shield mud, sealing with double-row rotary jet pile and pouring cover plate, which provided important engineering data for the construction of shield tunnel under tidal action. During the construction process, the Metro Line 4 Company and the construction party held expert consultation meetings for many times to optimize the construction plan and formulate emergency plans, and finally realized the completion of the two lines in Shailao section smoothly.

Line 4, with a total length of 30.9 kilometers, has 25 stations, passing through the old city of Shinan District, Fushan Back of Shibei District, Laoshan Scenic Area and other places. It is an east-west backbone line running through the middle of the city. The completion and opening of Metro Line 4 will significantly improve the quality of urban functions. At present, 19 stations on Line 4 have been closed and 18 sections have been connected. Subway Line 4 Company will continue to strengthen the construction site control, with a high sense of responsibility and sense of mission, always adhering to the concept of "operating the subway and serving the city", adhere to the quality, culture and science and technology guidance, Metro Line 4 will be the city's assured, satisfactory and quality project.