By Xinyi Li, EDITOR

The interconnection of rail transit, roads, tunnels, and bridges makes Chongqing a fascinating, three-dimensional city.

More than 80 residents and students visited the site to view the construction progress of the Hongyancun Bridge & Tunnel project contracted by China Construction Eighth Engineering Division (CEED for short), on June 16, the opening day of the construction site. Hongyancun Tunnel, a rare infrastructure project with four-story entrances and seven tunnels, once completed will give Chongqing a distinctiveness compared to many other cities.

Hongyancun Tunnel, with four stories and seven tunnels, will shorten the distance between districts in Chongqing, to be completed by 2020

The tunnel project is expected to be completed by the end of 2020. The journey from Shiqiaopu to Jiangbei District will be an easy ten-minutes once the Tunnel opens.

The Tunnel will astonishingly pass-through more than 2,000 existing buildings

The section of Hongyancun Bridge-Wutaishan Interchange, one of the three longitudinal expressway lines of Chongqing, is an integral part of Chongqing's expressway network. The steel-structured cable-stayed truss bridge above the Jialing River, designed for road-rail use, runs through the five districts of downtown Chongqing. It aims to establish a Line 5 connection across the river, creating astonishing three-dimensional transportation.

The bird's-eye view of the design sketch of Hongyancun Tunnel

The Hongyancun Bridge & Tunnel project is the middle section of the three longitudinal expressway lines of Chongqing. It starts from the north abutment of Hongyancun Bridge and ends at Wutaishan Interchange, with a total length of 4.95 kilometers. The main road has six lanes in both directions, with the designed speed of 80 km/h.

Hongyancun Tunnel is 3.72 kilometers long, connecting the southern bridgehead of Hongyancun Bridge and Shiyang Road, Jiulongpo District. It passes through multiple existing tunnels and over 2,000 buildings. The Hongyancun Interchange has a total length of 3 kilometers. The project is carried out in the Public-Private Partnership (PPP) with a total investment of 4.5 billion RMB.

The unique design to overcome a worldwide challenge

Notably, the design of the project is novel because of its four-story entrances and seven tunnels.

The four stories from the bottom up are the station of Line 9, Lishuwan-Caiyuanba Railway, Hongyancun Station of Line 5 and the main section of Hongyancun Tunnel and Xietaizi Connecting Tunnel.

The design sketch of Hongyancun Tunnel

According to Ding Ya, the project leader of Hongyancun Bridge & Tunnel, Hongyancun Tunnel is designed with left and right line branches. Hongyancun interchange overlaps with the station of Line 5, including Hongyancun Tunnel, the station of Line 5 and the connecting tunnel, Xietaizi Connecting Tunnel, Hongyancun Interchange, and Wutaishan Interchange.

“Above the tunnel complex is municipal rotary interchange and deep foundation pits with complicated structures. Experts at home and abroad have carried out more than ten discussions and evaluations from design to construction. Finally, they determined the bottom-up construction sequence. The whole construction is a testimony of overcoming a technical problem of tunnel complex construction faced around the world,” Ding Ya said.

The minimum distance between the tunnels is only two meters

There are four inherent challenges in the construction: the complicated and innovative structural design; the scale of the project; difficult organization and coordination due to the complicated surroundings; the high technical requirement and safety risk.

The minimum distance between the tunnels is only two meters

The tunnel complex is located at the halfway up a cliff with a height difference of about 80 meters. The minimum distance between tunnels is only 2.03 meters. The tunnel passes through more than 2,000 existing buildings, as well as six rail transit lines and railways. Therefore, those factors add complexity to the construction.

Several technologies are adopted to ensure the smooth construction, such as precise positioning construction of advanced large pipe shed, the technology of cross rock bolt and micro-vibration blasting techniques in the development of down-traversing loop lines and Line 1.

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Source: Chongqing Morning News