Beijing Daily∣updated: 31 January, 2021.

On January 30th, with the rotation of the cutterhead characterized by Peking Opera Masks, the East Sixth Ring Road Reconstruction Project is approaching a key point that the TBM with the largest diameter, named "Jinghua", has been finished commissioning and started the trial operation, which lays the foundation for the launch of TBM for the Western Tunnel Line. It is anticipated that by the end of March, the TBM will start launching from the north of the tunnel, and the TBM tunneling work of the East Sixth Ring Road Reconstruction Project will officially commence.

At the construction site, stacks of segments are piled up one by one. Looking down from the launching shaft side ground, we can see the huge TBM is lying in the ground and waiting for the order to move forward, while the cutterhead is now embedded in earth. Along the safety stairway down to the launching shaft, it can be seen the spacious TBM interior space which can accommodate five or six people walking through side by side.

The huge TBM, “Jinghua”

The tunnel section of the Reconstruction Project is approximately 7.4 km long, which will be constructed by shield tunneling method. The tunnel section is arranged with separated dual tunnel alignments, respectively bored by two super large-diameter slurry balanced shield machines, “Jinghua” for the west line and “Canal” for the east one. By the end of March, “Jinghua” for the west line will launch firstly, while the other TBM, “Canal” for the east line, will also launch one month and a half later on. The two TBMs will be operated along the two alignments simultaneously at a distance of 200 m.
The diameter of shield machine for boring subway tunnel is normally around 6m~7m long, while the diameter of the huge slurry balanced shield machines, “Jinghua” and “Canal”, reaches 16 meters, which is China’s largest-diameter TBM up to now.
The larger of the tunneling face, the larger of the excavated muck amount. It is understood that the amount of excavated muck reaches 202 cubic meters per meter of tunneling length, thereby requiring higher stability of the tunneling face and adaptability of the TBMs. The TBMs adopt the overall original design and system integration technique, and apply a number of core technologies such as cutter exchange under atmospheric pressure, telescoping main drive, high-efficiency transportation and assembly technology of super-diameter heavy-load segments, super high-power mud water circulation system and so on.

In view of the soft soil stratum in Tongzhou District in Beijing, the synchronous double liquid grouting system is adopted for the tunneling, enabling the solidification time to reduce from 8 hours to less than 1 hour, so as to realize rapid and stable construction and avoid ground surface settlement.

“The tunnel of the East Sixth Ring Road is not only the first expressway tunnel in Beijing constructed by TBM, but also the first tunnel in China to set an escape and rescue route is set below the traffic passage.” Wang Yuesong, head of the engineering department of the Reconstruction Project Management Office of Shoushou Group, said that the tunnel is divided into three layers, of which the upper layer is a smoke exhaust channel, the middle is the traffic passage, and the lower is the escape and rescue route.
Escape hatches will be set up at interval of 100 meters in the tunnel. Therefore, drivers and passengers will be able to descend the stairs from the escape hatch down to the rescue route in case of danger. In addition, the rescue route enables vehicles to pass through, and the rescue vehicles can also get to the designated location with the aid of the rescue route, which is convenient for rescue.

It is learned that the East Sixth Ring Road Reconstruction Project is a key project to implement the Beijing urban master plan and the Beijing sub-center detailed regulatory plan. The reconstruction project starts from the Beijing-Haerbin Expressway in the south and reaches Luyuan North Street in the north, with a total length of about 16.3 kilometers.
The project comprises direct widening work and underground reconstruction. The widening section is 7.1km long, and the underground section is from the south side of Beijing-Tianjin Highway to the north side of Luyuan Second Street, with the tunnel length of 9.2km. The tunnel is constructed by combination of cut-and-cover and shield tunneling, with a single shield tunneling length of 7.4 km.
(CCTV News’ Li Bo contributed to this report)