Innovating technology, breaking through difficulties and making every effort to get through the last 4.4 kilometers of Beijing-Tangshan intercity railway Beijing tunnel section project
The shield machine "Jingtong" is working at the excavation construction site of Yunchao Jianhe Tunnel. (Pan Zhiwang photo)
Not far from the Beijing City Sub-center Station under construction, the shield machine "Jingtong", the largest diameter high-speed railway tunnel in Beijing, is excavating underground at a speed of 8 rings per day. At present, only 4.4 kilometers of Beijing tunnel section of Beijing-Tangshan intercity railway has completed 50% of the total project, and the main structure will be completed by the end of 2024, laying the foundation for opening conditions by the end of 2025.
Although the sparrow is small and complete, the Beijing tunnel section project integrates innovative elements such as large-diameter shield tunnel, prefabricated U-shaped groove of subgrade and fully welded double V-shaped arch bridge. The Municipal Major Project Office, together with all parties involved in the construction, will strengthen scientific and technological innovation, practice new quality productivity, and strive to turn it into a demonstration project of the city sub-center.
"Intelligent Shield Machine" Tunneling "Without Changing Cutters"
Beijing-Tangshan Intercity Railway is a fast traffic corridor from Beijing to Tangshan. The project is divided into two sections. The first section from Songliang Road to Yanjiao was opened to traffic on December 30, 2022, and the remaining Beijing Tunnel is 4.4 kilometers long. Among them, the 1.3-kilometer-long Yunchao Jianhe Tunnel is not only the last tunnel in the whole line, but also the first large-diameter shield tunnel for high-speed rail in the sub-center area of Beijing.
"Swing mode, go!" On April 10, I came to the shield construction site located 31 meters underground. I saw that the yellow "big" shield machine stretched out the "sucker", picked up a segment weighing three or four tons, and slowly moved and rose. When it reached the joint with the previous segment, the jack exerted force and tightened the "nut" to tightly splice the two segments together.
"Every 9 segments can form a ring. Now this tunnel has completed the 309 ring and completed nearly half of the workload. By October this year, the internal structure construction of the tunnel will be completed. " Wei Zhe, deputy manager of the shield of the Eighth Bid Project of Jingtang Railway of China Railway 14th Bureau, introduced the shield machine "Jingtong" independently developed by China Railway Construction. The total length of the shield machine is about 138 meters, the total weight is about 3,200 tons, and the cutter head diameter is 13.3 meters. It is the largest high-speed railway tunnel shield machine in Beijing.
The shield section passes through the high-density medium sand stratum, with sand layer accounting for 85% and Shi Ying content reaching 60%, which accelerates the wear of cutter head and cutter. In order to enhance the tunneling ability, the project side tailored a sharp "tooth"-a three-layer cutter for "Jingtong" to reduce the wear during tunneling and optimize the opening rate of the cutter head, so as to finally realize one-time tunneling without changing the cutter. In addition, "Jingtong" is also equipped with optical fiber continuous and hydraulic wear detection devices, which can detect tool wear in real time and adjust shield tunneling parameters in time, so it can be called "intelligent shield machine".
Prefabricated U-shaped groove is greatly accelerated.
About 300 meters to the east of the shield launching shaft is a U-shaped groove of closed subgrade, from which the train will drive out of the ground in the future.
Compared with the fiery scene of the shield launching shaft, the scene of the U-shaped groove is slightly "cold and cheerless", which is a hidden mystery. Of this 461-meter subgrade, 216 meters are prefabricated and assembled with U-shaped groove structure, that is, factory centralized prefabrication, which is mechanically assembled like building blocks on site to achieve safe and rapid construction. It is the first case in the national railway engineering to build a U-shaped groove with prefabricated parts, which fills the technical gap in the assembly and construction of the U-shaped structure of subgrade.
Wei Zhe explained that prefabricated assembly has obvious advantages. In terms of personnel, the prefabricated assembly section only needs about 15 workers a day, while the number of people in the pouring section is 4 to 5 times that of the prefabricated section. In terms of time, it takes 15 days to pour the same 18-meter U-shaped groove, and only 5 days to lay it with prefabricated parts, which greatly shortens the construction period. In addition, the amount of steel bars and concrete in precast construction is reduced by 11% and about 45%, which is low in noise and pollution, in line with the trend of green development of buildings and resource conservation and utilization.
All-welded steel box arch bridge echoes "Jingfan"
Continue to go east, 80 meters east of the U-shaped groove, and the builders are simultaneously building an arch bridge.
From the design, this 79.75-meter-long white arch bridge is a double V-shaped suspender structure, which is shaped like a finger and contains the meaning of "victory" and "welcome". The overall shape is like two pairs of swallows flying with their wings spread, echoing each other with the hub "Jingfan" of Beijing Sub-central Station not far away.
The reporter learned that the arch bridge crosses Tongji Road, the main road of the city’s sub-center, and is close to beijing-harbin railway and Tongyan Expressway. In order to reduce the impact on the current traffic, the Municipal Major Project Office took the lead in organizing the participating units to optimize the cast-in-place concrete arch bridge with full support into a fully welded steel box arch bridge after many demonstrations. In the future, the construction will be carried out by the scheme of moving horizontally first and then pushing vertically, and the process of factory processing and on-site assembly will also greatly reduce the construction time.
"The arch bridge has adopted a brand-new lightweight design. The dead weight of the bridge has been reduced from 4,600 tons to 700 tons, and the steel consumption per linear meter is only 11.2 tons, which can greatly save the steel consumption. This is also the first time that truss steel box arches with sparse suspenders have been used in domestic railway construction. " Liu Lei, senior project manager of the engineering department of Jingtang Company, said that the bridge will also introduce magnetic unmanned video inspection equipment for the first time, which will make the daily maintenance of the steel bridge safer, simpler and lighter, reduce its own maintenance workload and improve the intelligent level of operation and maintenance. (Ren Shan)