Decoding Shenzhen Metro Line 7: How an Underground "Ballet" Was Staged
2016-11-01
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On October 28, 2016, as a brand-new metro train slowly pulled out of Xilihu Station, Shenzhen Metro Line 7 officially entered operation.
The 30.173-kilometer Line 7 is a BT project undertaken by Power Construction Corporation of China under the "investment and financing + design-build general contracting" model, linking from east to west Shenzhen's three most prosperous districts with the highest GDP and largest populations: Futian, Luohu, and Nanshan. Hydropower is PowerChina's forte, but building metros was almost a blank slate; over four years, the builders delivered an extraordinary set of answers.
Building Stations: Civilized Construction Overcoming Every Obstacle
Digging Tunnels: "Underground Giants" Passing Through Buildings and Under Rivers
Shenzhen Metro Line 7 is known as a "geological museum"; nearly half its area was formed by land reclamation. Across the line's 21 shield-driven sections, the tunnels passed beneath buildings, rivers, railways, stations, expressways, and metro tunnels multiple times, with 35 major risk sources along the route. Tunnel excavation broke through obstacle after obstacle.
The shield machine is the "underground giant" of metro tunnel excavation, and shield construction is high-risk work; with dozens of shields launched simultaneously, many industry experts were on edge.
Feng Hongchao, a veteran of hydropower and a veteran model worker, is a renowned innovator. Half a year before construction, he and his shield machine team were still "shield machine illiterates"; through diligent study, they quickly mastered the technology, overcoming one obstacle after another—passing beneath shops and residential buildings, under rivers and reservoirs, and through permeable strata, granite layers, and complex geological formations. Four five-story dilapidated buildings without foundations stood above the path of the Dayu shield machine; the buildings remained intact with "zero settlement." After nearly 300 days of underground travel, the team safely and with high quality completed all shield tasks in its section.
Caihong Bridge is a key transport hub connecting Futian and Luohu Districts. During excavation, the shield machine was blocked by the pile foundations of eight approach-bridge caps; the engineering team used pile foundation underpinning to remove this "roadblock."
While excavating the section from Chaguang Station to Zhuguang Station, the team encountered boulders, and the Kaituozhe shield machine could not advance. The builders used down-the-hole drills to locate the boulders, drilling and blasting precisely to peel away the boulders layer by layer, allowing the shield machine to pass the obstacle. Afterwards, the engineering team summarized its experience and established a networked remote monitoring system for three shield machines; subsequently, in other shield sections, the Kaituozhe passed through boulder clusters eight times with the shield machine intact.
Tanglang Mountain, with a total length of 10,260 meters, has hard rock strata, so only the mining method could be used. The tunnels passed beneath Beihuan Boulevard five times and beneath the Beijing-Hong Kong-Macau Expressway four times, repeatedly "brushing past" residential areas. The tunnels have 77 cross-section types, some with a cover depth of only 6 meters and a thinnest separation from the surface of just 1.5 meters, with the minimum distance between two tunnels only 30 centimeters; excavation could easily cause ground heave or settlement. Project manager Zhang Yeqin led the engineering team in continuous observation and study and in researching construction methods. On November 25, 2014, all mining-method tunnel groups were holed through, with deviations controlled within 10 millimeters—50% more precise than code requirements—and a 100% pass rate.
If station and tunnel construction is compared to a symphony, then track laying, installation and finishing, and commissioning are like dancing ballet underground on tiptoe.
Shenzhen Metro Line 7 has 93.2 kilometers of track in total, including 69.72 kilometers on the main line. Construction involves seven processes, each requiring precision to the minute and second, with track alignment accurate to plus or minus 0.01. To speed up track laying, the project department increased the number of track-laying stations from three to four, advancing at a rate of one kilometer per day. To ensure installation precision, the project department introduced the "CP III" high-precision survey technology to improve track control quality and enable data sharing between track construction surveys and operational surveys. To reduce noise, the engineering team adopted vibration- and noise-reduction measures such as track bed mats and steel-spring floating slab concrete track beds. To ensure smoother, more comfortable train operation, the project department actively cooperated with Shenzhen Metro Company in testing non-ballasted track slabs, successfully completing the task.
Construction workers told reporters that the Line 7 installation works are a massive systems project involving 14 disciplines, including architecture, structures, conventional ventilation, water and electricity, communications and signaling, integrated supervision, ticketing systems, and fire protection systems. Nearly 500 Chinese and foreign manufacturers supplied equipment, and more than a dozen installation contractors worked in coordination, installing a total of 70,000 units (sets) of equipment; water pipes total 2,500 kilometers, and optical cables, power cables, and grounding grids reach 100,000 kilometers—equivalent to two and a half times around the Earth.
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