At the construction site of Dahongmen Station on Phase III of Metro Line 8, two large cranes raised over 60-meter-high booms to insert a 40-ton “steel reinforcement cage” into the ground. The Municipal Rail Transit Construction Management Company revealed that Dahongmen Station, a key interchange station on Phase III of Line 8, has fully started construction and will allow transfers to Line 10 in 2017.
A dozen meters north of Dahongmen Station on Line 8 is the Liangshui River; water seepage could adversely affect the station's deep foundation pit. In addition, during Beijing's rainy season, the river rises rapidly, posing a risk of backflow into the pit. To block river water and groundwater seepage, the project adopts a special construction method of underground diaphragm walls: trenching machines dig several seepage-proof trenches around the site, and giant “steel reinforcement cages” 6 meters wide and 43 meters high are inserted into the trenches before concrete is poured, effectively forming a continuous reinforced concrete wall underground around the station to keep groundwater and river water out of the station area. According to estimates, this construction method costs twice as much as traditional dewatering construction but saves the extraction and discharge of over 100,000 cubic meters of groundwater. According to the relevant person in charge from the construction contractor China Railway 11th Bureau, Dahongmen Station requires 77 concrete walls; 32 diaphragm wall panels have been completed so far, and the remaining 45 are expected to be finished by the end of the year.

Dahongmen Station on Line 8 is a three-level underground station, one level more than conventional stations. The first basement level is the equipment floor, the second is the concourse, and the third is the platform. The three-level design is mainly due to insufficient construction space, which shortened the station from over 200 meters to 185 meters. Dahongmen Station will enable single-passage two-way transfers with the existing Line 10, and the transfer passage is only 60 meters long, meaning citizens need to walk only about two minutes to transfer.

Phase III of Line 8 is the southern extension of Phase II, running from south of the National Art Museum in the north to Yinghai in Daxing in the south, with a total length of about 20.7 kilometers and 16 stations. Except for Demaozhuang and Yinghai stations in the southern extension, all are underground stations. As it passes through bustling commercial areas such as Wangfujing, Qianmen, and Zhushikou, construction difficulty increases; Phase III of Line 8 will adopt a phased opening model, with the section from Zhushikou to Yinghai expected to open in 2017. There is no clear timetable for the connection between the northern section from Qianmen to Wangfujing North and the National Art Museum on Phase II of Line 8, but it is expected to open as early as 2017. Once completed, Phase III of Line 8 will form an underground central axis nearly 50 kilometers long running through the north and south of the city together with Phases I and II, alleviating traffic congestion in the central urban area.