People's Daily - Guizhou Channel
Dejiang Special Tunnel Passing Ceremony Site. Photo by Li Yu
People's Daily Dejiang, October 20 (Li Yu) At 15:00 on October 20, the Dejiang Special Long Tunnel, built by Guizhou Highway Development Co., Ltd. and constructed by Guizhou Road and Bridge Group Co., Ltd., successfully achieved double-spread penetration. This, known as the most difficult highway tunnel in Guizhou, has made a phased breakthrough after 50 months, taking a solid step for the early completion and opening of De(Jiang) Wu(Sichuan) Expressway.
Dejiang Special Long Tunnel is completed. Photo provided by Guizhou Road and Bridge Group
Dejiang Special Long Tunnel is a key project of the De(Jiang) Wu(Chuan) Expressway. The left hole of the tunnel is 5,505 meters long and the right hole is 5,425 meters long, of which the maximum buried depth is about 537 meters. After the highway is completed, the spatial distance between Dejiang River and Wuchuan, Chongqing and Wuling Mountain areas will be further narrowed, and it is a fast channel for the northeastern Guizhou region to integrate into the Chengdu-Chongqing Economic Zone and the Yangtze River Delta Economic Zone.
Dejiang Special Long Tunnel is located in the overly sloped area from the Wuling Mountains to the Dalou Mountains in the northeast of the Guizhou Plateau. The surrounding rocks are broken and the cleft rocks are developed. In addition, there is a underground river and a reservoir inside the mountain. The hydrogeological conditions are extremely complex, with high technical difficulties, high safety risks and many uncertain construction factors. It is considered to be the hardest "hard bone" on the whole line.
The drilling hole in the left hole of Dejiang Special Long Tunnel discharges water from the right hole. Photo provided by Guizhou Road and Bridge Group
In August 2016, the Dejiang Special Long Tunnel officially started construction. Although the tunnel construction is difficult, the builders worked hard to overcome many difficulties and continuously promote the tunnel to enter. In October 2017, the total left and right tunnels of the tunnel were 5471m in just one year, and the construction of the entire line was smoothly over half. Such development momentum made the builders full of confidence in the early completion of the project construction.
Tunnel water is discharged. Photo provided by Guizhou Road and Bridge Group
Until December 2017, a large amount of rushing water began to appear during the excavation of Dejiang Special Long Tunnel. The rushing water began to flood from the palm surface to the vicinity of the arch in just 30 minutes. There was also a high water pressure that directly penetrated a fill-type crack. The rushing water flooded the left and right holes at the exit end of the tunnel. The peak water inrush reached 14,900 cubic meters per hour, which was equivalent to the sum of the water volume of 7 standard swimming pools, which is very rare in Guizhou and even in the country.
"Although there was a possibility of water gushing before construction started, the actual situation was beyond the initial expectations." Jin Junqi, chief engineer of the second contract section of Dewu Expressway, said that during the rainy season, the water gushing in the tunnel reached 14,900 cubic meters per hour, and the usual water gushing also reached 1,500 cubic meters per hour, posing severe challenges to tunnel construction.
High pressure water in the tunnel. Photo provided by Guizhou Road and Bridge Group
The problem of water rush is not solved, and the tunnel construction cannot be restored to normal. However, in such a large amount of water gushing, how to drain and block the water in time while ensuring the safe and effective progress of the construction progress has become the top priority of the project department at present.
To this end, the project department invited experts to take the pulse and consult the country. In the first half of 2018, expert meetings and special meetings were held at the construction site for drainage, risk avoidance, construction technology, quality improvement, etc. in the construction of the Dejiang Tunnel. In March of the same year, during repeated attempts, the project department gradually summarized and explored the "membrane bag grouting water blocking method" and "fast-greasing paste slurry high-pressure grouting water blocking method", and established the treatment plan of "blocking as the main, blocking and interception as the combination, and drainage as the auxiliary".
The underground river water overflows in the tunnel. Photo by Li Yu. After the plan was determined, in order to ensure the quality of tunnel construction and the safety of workers, Jin Junqi led the workers to excavate little by little. Every time the palm surface of the tunnel was promoted, super drilling technology was first used to detect the depth of 80 meters in front of the palm surface. At the same time, in order to prevent the increase in water gushing during the rainy season and affect the construction, a drainage ditch was dug to discharge the accumulated water flowing into the tunnel in time. Despite this, it took nearly a year for the entire tunnel to advance 1 kilometer.
Under the difficulties, all builders have rushed to build time and progress, and have safe and civilized construction, and have continuously overcome the problems that have arisen. In June this year, the construction of Dejiang Special Long Tunnel ushered in a critical node victory: the right hole was successfully completed; on October 20, the left hole of the tunnel was also successfully completed.
The tunnel was first exposed to water gushing during construction. Photo provided by Guizhou Road and Bridge Group
In addition, the "Research on Key Technologies for High Pressure Water Congestion in Karst Area inclined Section Highway Tunnel" based on Dejiang Special Long Tunnel has been approved by the Guizhou Provincial Department of Transportation. Currently, relying on the high-pressure water inrush treatment technology of tunnels, 1 highway construction method, 4 enterprise-level construction methods, 9 papers, and 3 patents have been formed, providing valuable solutions for the construction of water-rich tunnels across the country.
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