Project Update | The two tunnels of the Dafengding Tunnel on the Lexi Expressway have been successfully connected

On April 1st, with the last "barrier" on the left tunnel of the Dafengding Tunnel in the S1 section of the Lexi Expressway being broken through, the two tunnels of the Dafengding extra-length Tunnel of the Lexi Expressway, constructed by the Machinery and Chemical Branch and the Tunnel Branch of the Road and Bridge Group, were successfully connected, marking a significant progress in the construction of the Mabian to Zhaojue section of the Lexi Expressway.

The Dafengding Tunnel is located in Mabian Yi Autonomous County, Leshan City. The left tunnel is 5,680 meters long and the right tunnel is 5,699 meters long. It is situated in the upper half of the 64-kilometer-long longitudinal slope of the Lexi Expressway in the Hengduan Mountains, with a maximum burial depth of 1,006 meters. It is a micro-gas extra-long tunnel, and the rock type of the stratum is mainly carbonaceous shale. It passes through faults and geological fragmentation. The tunnel runs through the Mabian Dadu River Forest Farm and the Ma Mize Provincial Nature Reserve. It is densely covered with first-class protected plants such as Davidia involucrata. The average annual rainfall reaches 270 days, and the winter ice and snow period lasts for three months. Coupled with the complex geological conditions in the water-rich area, the construction difficulty is extremely high.

In the early stage of construction, the project was confronted with the "three no's" problem of "no access road, no communication signal, and no power guarantee". It took two years to complete the construction of 22 kilometers of access roads, build two temporary communication base stations, and set up 30 kilometers of temporary power lines, laying a solid foundation for the project's construction.

To reduce damage to the ecological environment, the project initiated the optimization procedure of the protected area in 2018. In August 2020, it was approved by the provincial government to adjust the functional areas. At the same time, it actively promoted the application for changing three Bridges into one road, saving 106 million yuan in costs, reducing 850,000 cubic meters of waste residue and 80 mu of temporary land. The project also ingeniously adopted a water-jacking operation construction plan. By increasing the water exploration distance and forecast frequency of the advanced drilling, it implemented comprehensive technical measures of "prevention, blocking, interception, drainage and diversion", and iteratively upgraded the reverse slope drainage system, forming a construction method of "double tunnel integration, one-stop operation, and separation of clean and sewage", effectively controlling the risk of water and mud gushing in the tunnel. Achieve a dual reduction in energy consumption and pollution control costs.

During the construction process, the project actively promoted the matching of large-scale tunnel construction machinery, adopted mechanical equipment such as rock drilling jumbos, applied advanced detection hole densification prediction, and popularized energy-concentrated smooth blasting and wet shotblasting techniques, achieving a dual improvement in safety and efficiency. At the same time, scientific research and technological breakthroughs were carried out around difficult problems such as reverse slope water pumping, resulting in 4 research projects, 1 invention patent, 3 software Copyrights, 5 papers and 2 utility model patents, filling the technical gap in mountain tunnel water pumping and drainage.

Extended Reading

The successful breakthrough of the two tunnels of the Dafengding Tunnel this time has pressed the acceleration button for the opening of the Lexi Expressway. As the first expressway in Sichuan Province to extend deep into the hinterland of the Greater and Lesser Liangshan Mountains, the opening of the Lexi Expressway will put an end to the history of the three counties of Zhaojue, Meigu and Leibo in Liangshan having no expressway access. The driving time from Mabian to Zhaojue will be reduced from 5 hours to 1.5 hours, and it will only take 3.5 hours to travel from Zhaojue to Chengdu. At the same time, the Lexi Expressway will also connect the Chengdu-Chongqing Twin-City Economic Circle and the Panxi region, effectively alleviating congestion on the Ya 'an-Xi 'an Expressway, activating rural revitalization and eco-tourism along the line, and promoting the construction of a comprehensive transportation hub in the western region.