The Xincheng-Kunming Railway crossing the “Geological Museum”

  More than 60 years ago, the completion of the Laocheng (Chengdu City, Sichuan Province) Kunming (Kunming City, Yunnan Province) railway wrote the miracle of human conquest of nature. More than half a century later, on June 21, 2022, the Xiaoxiangling Tunnel, the core control project of the Xincheng-Kunming Railway in the 21st century, was successfully completed, marking the completion of the new-Chengdu-Kunming Railway tunnel under construction. This is not only a continuation of the legend of the old Chengdu-Kunming Railway, but also another challenge to the limit by Chinese railway builders.
  What geological problems did you encounter during the construction of the Xincheng-Kunming Railway? How did the Chinese railway builders use the power of science and technology to overcome these problems?

Chengdu-Kunming Line Shupu Station is the meeting station of the new and old Chengdu-Kunming Railway (Photo/Luo Chunxiao)
The “stumbling block” on the Xincheng-Kunming Railway

  In 2007, the new Chengdu-Kunming Railway, with a total length of 860 kilometers, officially started construction. The new-Chengdu-Kunming Railway is roughly parallel to the old-Chengdu-Kunming Railway, and the bends are straight. The tunnel is the main way to “straighten” the line.
  Whether it is the old-Chengdu-Kunming Railway or the new-Chengdu-Kunming Railway, the railways along the railway are all steep mountains, densely covered with deep ravines, vertical and horizontal ravines, and extremely complex topography and geology. They are called “geological museums” and have been asserted by foreign experts as “railway forbidden areas”. .
  Tunnel construction is faced with engineering geological difficulties such as water gushing, sand gushing, landslides, active faults, fault fracture zones, large deformation of soft rock, rock bursts, and high ground temperature.
  Take the Xiaoxiangling Tunnel, the longest tunnel on the Xincheng-Kunming Railway Line, as an example. Water damage, that is, water gushing, is the biggest “stumbling block” in the construction process. The large amount of water and the high risk are rare in China.
  Water inrush refers to a dynamic damage caused by the sudden change of the hydrodynamic conditions and the mechanical balance of the surrounding rock due to the destruction of the aquifer structure due to the tunnel excavation, so that the energy stored in the groundwater body is instantaneously released in the form of high-speed fluid migration. Phenomenon.
  Water inflow is one of the geological disasters second only to landslides in tunnel construction. The main sources of water are surface water, karst caves and underground river water, old pit water or ancient mine water, aquifers and fault water.

During the construction of the Xiaoxiangling Tunnel, there was a sudden water gushing (Photo/China News Agency reporter Liu Zhongjun)

  In the process of tunnel construction, the stress of the surrounding rock of the tunnel (the strength of the internal force per unit area in the rock surrounding the underground cavern) is often caused to relax or concentrate, which will damage the surrounding rock and reduce the effective protection thickness of the water barrier. small, resulting in a decrease in the stability of the surrounding rock, thereby increasing the risk of water inrush in the tunnel.
  In addition, the water inflow volume of the tunnel varies with the topographic and geomorphological conditions and the location of the tunnel. The longer the tunnel, the more hydrogeological units it passes through, and the larger the catchment area and supply range, the greater the unit water inflow volume.

The fully computerized three-arm rock drilling rig performs drilling and blasting operations to realize intelligent positioning and fully automatic, efficient and intelligent drilling, with fast rock drilling speed, high safety factor, and good blasting effect (Photo courtesy of Guo Jing)

Wet spray manipulator with a working range of up to 16 meters for shotcrete (Photo courtesy of Guo Jing)
How to overcome the hard bones that are difficult to “gnaw”

  At the beginning of the design, the Xiaoxiangling Tunnel set up a herringbone drainage slope in the middle to deal with the possible serious water inflow problem. During the construction process, the builders adhered to the principle of “controlling water first, controlling water first, releasing pressure first, and releasing pressure first”, introduced domestic advanced fully computerized three-arm rock drilling rigs, wet spraying manipulators and other large-scale tooling equipment, and adopted exploration methods. Various measures such as water, drainage, drainage, and diversion have been adopted to improve the geological conditions of surrounding rocks and greatly reduce the frequency and scale of risks. By adding a water stop wall, the water inflow is discharged to the natural river channel through the horizontal hole, or the drainage channel is deepened and widened to increase the drainage volume, and finally the water inflow is “tamed”.
  In the process of tunnel excavation, the soft rock of the mountain is easily deformed due to the change of stress (meaning that the force has been changing over time). To solve the deformation problem, it is necessary to decompress the rock mass, as shown in the figure, that is, the tunnel section needs to be enlarged to reserve a deformation space. The construction personnel use steel arches for reinforcement, and lock the protruding irregular rocks in the arch. on the shelf.

In order to prevent the tunnel wall from collapsing, it is necessary to expand the section, reserve the falling area due to gravity in advance and reinforce it (Photo/Ma Xiao)

Under the action of tectonic movement, the rock layer is bent due to the force. A bending is called a fold. If a series of wave-like bending deformation occurs, it is called a fold (Photo/Ma Xiao)

  According to statistics, during the construction of the Xiaoxiangling Tunnel, a karst dark river was encountered, and the accumulated water inflow exceeded 200 million cubic meters, which is equivalent to the water volume of 15 West Lakes. In the face of every emergencies, the builders are calm in the face of danger, face the difficulties, and use scientific methods to calmly deal with them, so that the construction can proceed smoothly.
  Finally, the Xiaoxiangling tunnel passed through 10 faults and 2 folds, and the tunnel body passed through a soluble rock section of about 4.5 kilometers. After more than 2,200 days of hard work, it ushered in the victory of the whole line. Up to now, of the 6 sections of the Xincheng-Kunming Railway expansion project, 5 sections have been completed and put into operation.
Knowledge link
The old-fashioned Chengdu-Kunming Railway that bravely broke into the “Railway Restricted Area”

  In the 1960s, more than 300,000 railway builders built a world-renowned mountain railway, the Chengdu-Kunming Railway, among the high mountains in southwest China. Most, together with the Apollo moon landing and the first artificial satellite, it was called by the United Nations “the three major miracles that symbolize the conquest of nature by mankind in the 20th century”.
  The Laocheng-Kunming Railway was built in 1958 and completed and put into operation in 1970. With a total length of 1085 kilometers, it is a major transportation artery running through the southwest and northwest regions of China.
  At that time, the level of construction and equipment in China was relatively backward. The rails were all lifted and transported manually. The construction of the tunnel was entirely dependent on the builders using sledgehammers and steel drills to drill and blast holes. …The older generation of railway builders persevered and overcame all difficulties. After 12 years of arduous struggle, they cut through hundreds of mountains, built 427 tunnels, and erected 991 bridges, finally turning the insurmountable moat into pass.

Old-Chengdu-Kunming Railway Guancunba Station (located in Leshan City, Sichuan Province)

  The Xincheng-Kunming Railway once again crosses the “Geological Museum” and is expected to be fully connected by the end of this year. After the new Chengdu-Kunming Railway is completed and opened to traffic, the old and new Chengdu-Kunming lines will be separated from passenger and freight. The new and old “Road to the Moat” will jointly help local economic development along the line and write a new chapter in railway construction and development!