A Glimpse of the First Yuanjiang River Crossing Tunnel
Media reporters and on-site construction personnel witness the significant moments of the whole route connection.
At 11:23 am on July 4, with an 11.75-meter-diameter and 3,000-tonne "Yuan An" shield machine broke out, the west line of the Yuanjiang River Tunnel got the whole line connection. So far, the construction of the two-way east-west line of the Yuanjiang Tunnel has been completed. According to the introduction from project leader Lu Kaidao, the “Yuan An” shield machine, the first domestic large-diameter atmospheric pressure tool mud-water balance shield machine, designed and developed by China Railway Construction Heavy Industry Corporation Limited, is listed among the national key research and development projects. With the completion of the Yuanjiang River Tunnel, it serves as a historical land mark as the construction of China's underwater shield tunneling machinery and the construction technology of shield tunnels under complex geological conditions to reach the world's advanced level.
The construction of the Yuanjiang tunnel project starts from Yangming Road in Jiangnan urban district in the south and reaches the Zaoguo Road in Jiangbei urban district in the north, including underground tunnel civil engineering, electromechanical systems engineering, management center houses and other supporting facilities. The length of the single line of the tunnel is 2,240 meters, of which the shield section is 1,680 meters. It adopts a double-hole single-layer form with a net width of 18 meters and two-way four lanes. The road design speed is 60 kilometers per hour. On October 16, 2016, the construction of Yuanjiang Tunnel officially kicked off. On September 28, 2017, the “Yuan An” shield machine, which was responsible for the construction of the shield section of the Yuanjiang River Tunnel, officially passed the QC and got the verification by Changsha Railway Construction Heavy Industry Corporation Limited. On December 28th, the “Yuan An” shield machine got initiated and the Yuanjiang River crossing mode started running. On October 9, 2018, the connection of the east line of the Yuanjiang Tunnel was successfully finished. After the completion of the cross-river tunnel, Jiangbei was grounded about 100 meters south of Yucai Road, and Jiangnan was grounded about 85 meters north of Longyang Road. The tunnel connecting roads in Jiangbei are Renmin Road and Chun'an Road, and in Jiangnan are Shande Road (planned) and Linyi Road. The tunnel has greatly narrowed the distance between Jiangbei and Jiangnan urban districts. One can drive across the river within 5 minutes under the most optimistic traffic condition, which will significantly ease the public traffic pressure.
At the scene, the correspondence takes the construction vehicle into the East Line Tunnel for an experience. The whole journey takes about 8 minutes to reach Yangming Road in Jiangnan from Zaoguo District in Jiangbei. Reinforcement construction and related ancillary works are still underway at the site, and it is estimated that the tunnel can be passed in 5 minutes after the whole line is opened. The reporter is informed by the construction project contractor that the tunnel is expected to open to mass public traffic use in this October. By then, it will greatly enhance the intensity of cross-strait connections, and will give a boost towards the promotion of the economic and social development of Jiangnan urban district and realize "coordinated development on both sides of the river."
The Yuanjiang River Crossing Tunnel exists as a part of the main road of Zaoguo Road to Yangming Road, which belongs to the 16 main trunk roads planned by Changde Municipal Government. It is located in the middle of the “S” curved section of the Yuanjiang River between the First Bridge and the Third Bridge of this river, about 2.2 kilometers from the First Yuanjiang River Bridge in the upstream, about 2 kilometers from the Second Yuanjiang River Bridge in the downstream of the Yuanjiang River Bridge. The nearest port is the Luo Lukou Port in the upstream, about 1.5 kilometers away. The tunnel is the control project of Changde City's “13th Five-Year Plan” in the era of big city construction, which is of great importance for the integration of Jiangnan and Jiangbei.
The total investment of the river crossing tunnel is RMB 2.544 billion yuan, which has been included in the third batch of PPP demonstration projects of the Ministry of Finance. The tunnel has a total length of 1,680 meters and an outer diameter of 11 meters. It is a two-hole two-way four-lane design with a design speed of 60 kilometers per hour. There are no ramps at the entrances and exits of the tunnel, and the vehicles are connected to the tunnels by bypassing the surrounding roads. The entrance and exit of the Jiangbei tunnel is located at Zaoguo Road and the entrance and exit of the Jiangnan tunnel at Yangming Road. After the tunnel is put into use, it is estimated that the river crossing duration of the vehicles can be shortened by 10 to 20 minutes.
When studying how to construct the Yuanjang River crossing channel, the municipal party committee and the municipal government once compared the two schemes of building a bridge and building a tunnel. The river regime of this section varies greatly. If the location of the bridge construction scheme is unfavorable, it will have a serious impact on the river channel, and it will be greatly affected by severe weather such as heavy rain, snow and ice. The project asks for a high investment cost and a construction area of large land acquisition, which will exert a certain impact upon the landscape along the river. Moreover, the comprehensive construction cost of the bridge construction scheme (including demolition fee) is much higher than that of the river-cross tunnel plan, considering the comprehensive navigation conditions, flood control impact, environmental impact and operating conditions.
After completion, the tunnel will not affect the landscape and operation of some institutes within the area, such as Changde 5th Middle School, Qu Yuan Park and Jiangnan Bund Park (planned), and can avoid the coordination problems caused by the massive demolition of the city. In addition, the tunnel scheme has no impact on navigation, flood control and surrounding environment. It can be used all day long and is conducive to the development of surrounding commercial plots. At present, in the cities along the Yangtze River in Changsha, Wuhan, Nanjing, Hangzhou, Shanghai, etc., in order to protect the scenery along the Yangtze River and reduce the amount of demolition in densely populated urban areas, the urban cross-river transportation construction method of “bridge and tunnel” is adopted, and the overall taste of nature and humanity in the city will get promoted.
Via technical and economic comparison, the two-pipe single-layer four-lane scheme is well connected with the cross-strait planning roads, not to mention the tunnel entrance and exit and crossroads with appropriate waiting length. The construction and operation process has less impact on the surrounding buildings, and the tunnel length is shorter. The operating conditions meet the required standard. All these factors considered, the cross-river tunnel adopts a double-pipe single-layer four-lane scheme on the blue chart.
The Yuanjiang River Crossing Tunnel will be constructed by implementing the shield method and once formation technology, and will be constructed with the large shield of the China Railway 14th Bureau Group, which is the first large shield engineering company that has been set up in China recently, focusing on the large shield profession. The company has 14 sets of mud-water balance shield machines produced at home and abroad. The original value of the equipment reaches RMB 2.3 billion yuan with various types of diameter of 6.2 meters to 15 meters, which has been successfully applied to high-speed rails, urban subways, cross-sea tunnels and other construction areas. The China Railway 14th Bureau Group has achieved a high reputation and finished a number of high-quality projects such as the National Quality Engineering Gold Award, Nanjing Cross-river Tunnel, etc. Bound with the core technology of cross-river tunnel construction, the institute is the professional engineering company with the most construction competence, reliable equipment and technical strength in China.
Lu Kaidao, the project manager of the river-crossing tunnel from the China Railway 14th Bureau Group says, this cut size of tunnel section is unimaginably large, which is close to the height of a four-storey building. The full-section gravel stratum is 3,000 meters long, and the maximum strength of the pebbles is 73 MPa, which is harder than the average level of a common rock. Considering the abrasiveness is strong and the tool wear is serious, it is necessary to replace the leading blade once every 50 meters. In order to reduce the risk of long-term downtime, more than 300 large-alloy tools with higher wear resistance were specially developed, and 278 replacements were consumed in the construction of the entire tunnel. As the largest underwater shield tunnel project in Hunan Province and the first cross-river tunnel in the Yuanjiang River, there are no small problems in construction, mainly due to the complicated geological conditions. As noted before, the total length of the tunnel shield section reaches 3,360 meters, of which the full-section gravel stratum is up to 3,000 meters long, and the maximum strength of the pebbles is 73 MPa, and the abrasiveness is strong. Within the earth depth in that area, the formation is rich in confined water with large permeability coefficient, maximum water pressure reaching 4.8 times atmospheric pressure. In the double-line tunneling process of the shield machine, it is necessary to cross the levees on both banks of Jiangnan and Jiangbei four times. In the end, the construction team handled the mud professionally by adopting a new atmospheric pressure changing system and centrifugal equipment, which solved the above problems and ensured the smooth construction of the tunnel.
It is reported that the tunnel construction with the targeted design of the "Yuan An" shield machine is listed as the national "863" major science and technology special project, which is ranked as the first large-diameter atmospheric pressure change mud-water balance shield machine in China, with the Chinese complete independent intellectual property rights. The shield cutter has a diameter of 11.75 meters, a length of 132 meters, and a weight of 3,000 tons. The atmospheric pressure change tool is 4 to 5 times more efficient than the normal pressure change tool. The comprehensive penetration of the tunnel indicates that China's large-scale underwater tunneling machine manufacturing technology and complex underwater tunnel construction technology have reached the world advanced level.
Mr. Shi Zhong, the chief engineer of the Yuanjiang Tunnel Project Department from the China Railway 14th Bureau Group tells the correspondence, since the tunnel excavation section is grand large and the hydro-geological conditions are complex, plus the stratum rich in confined water and keeping the characteristics of high strength, large permeability coefficient and high water pressure, the two-story flood control embankment, the three-storey building above the dam gate and the main channel of the river are listed as major sources of construction risk. The top of the tunnel is only 4.3 meters from the bottom of the building on the ground. Building protection is a difficult job and construction risks are hardly getting low. The seasonal variation of the water level in the Yuanjiang River is also noticeable and cannot be turned a blind eye to. The water level in the flood season reaches 39 meters or higher, which is 6 meters higher than the urban area on both sides of the river. It is in the form of “ground overhanging river”. Today, the tunnel traverses smoothly across the Jiangbei flood control embankment, marking the four major risk sources of the tunneling phase have all been conquered.
An ordinary worker of China Railway Construction Heavy Industry Corporation Limited is interviewed at the construction site. He is Zhang Zhengmiao, 25 years old. Coming from Shandong, for the sake of the construction of the Yuanjiang River crossing tunnel, he only went home three times in three years. Today, upon the connection of the whole line, he is quite delighted with a shy but proud smile on his face. He tells the reporter that when the whole project gets finished he can go home and get married. “My girlfriend has been waiting for me for 3 years,” he says.
Please refer to eng.changde.gov.cn when using this article
Translator: Wu Yangyue
Chinese source: http://news.yantuchina.com/41806.html