Changning Tunnel on Changbao Expressway in Yunnan Province is fully completed!

On January 5, 2023, the Changning Tunnel on Changning-Baoshan Expressway in Yunnan Province (hereinafter referred to as "Changbao Expressway") invested and constructed by Guangxi Road and Bridge Engineering Group, a company directly under Guangxi Beibu Gulf Investment Group, is completed after four years and five months of hard work. It means that the "stuck neck" problem of the Changning Tunnel has been solved.

The Changning Tunnel is extra-long, a two-way, four-lane separated tunnel with a length of 5454 m on the left section and a length of 5429 m on the right section. The Changning Tunnel is located in the Hengduan Mountains in western Yunnan, which is one of the "bottleneck" areas with the most difficult tunnel construction, the highest engineering risk and the most complicated geological conditions. It has five major engineering challenges during the construction: (1) extraordinary serious rock weathering; (2) serious impact of horizontal tectonic stress; (3) developed joint fissure; (4) high content of clay mineral and low rock strength; and (5) severe softening and disintegration after the surrounding rock absorbs water,. As a result, engineering geological disasters occur frequently during the construction process, such as large deformation of soft rock, water gushing, mud inrush and collapse, etc. The problem of large deformation of asymmetric soft rock is particularly prominent, with the maximum deformation being 2125 mm, the arch replacement rate being as high as 33%, which makes the construction progress slow. The Changning Tunnel is the "stuck neck" project of the Changbao Expressway, and it is also one of the most difficult tunnels under construction in Yunnan. In 2020, relying on the Guangxi Research Center of the State Key Laboratory for Geomechanics & Deep Underground Engineering, the excavation compensation method and the high-stress NPR anchor cable excavation compensation support technology invented by Academician Manchao He was applied to the treatment of large deformation of soft rock by Guangxi Road and Bridge Engineering Group to help solve the challenging problem of large deformation tunnel construction in soft rock through joint research. The goal of "three zeros and one no" with zero arch replacement, zero intrusion, zero surge and no renovation has been achieved, and the construction period has been saved by 7 months. The safety benefits, social benefits and economic benefits are remarkable. The evaluation of scientific and technological achievements has been completed, reaching the International advanced level. It means that the high-stress NPR anchor cable excavation compensation support technology has successfully solved one worldwide problem of large deformation of soft rock, and has demonstrated new achievements in helping the construction of transportation infrastructure.

During the project implementation, Academician Manchao He visited the site of Changning Tunnel several times to investigate and guide the implementation of the high-stress NPR anchor cable excavation compensation support technology, and conducted technical exchanges with Guangxi Road and Bridge Engineering Group and all parties involved in the construction. After the high-stress NPR anchor cable excavation compensation support technology was applied to the Changning Tunnel with a cumulative construction length of 1187 m, which greatly improved the construction safety and engineering quality.  All parties agree that the new NPR material and the matching high-stress NPR anchor cable excavation compensation support technology are the "golden key" to solve the problem of large deformation of soft rock tunnels, and that they will play an important role in major national projects such as the Sichuan-Tibet Railway and the Central Yunnan Water Diversion Project, and will have broad application prospects.

On the afternoon of January 5, 2023, the key technology forum for the construction of large deformation tunnels in soft rock was successfully held along with the opening ceremony for the Tunnel. Academician Manchao He was invited to give a lecture on the excavation compensation method, explaining the excavation compensation method that is parallel to the Platts pressure arch theory method and the New Austrian Tunneling Method (NATM), and clarifying the relevant mechanical principles. The extraordinary mechanical properties of the new NPR material are introduced in detail. New theories, new materials and new technologies lay the foundation for solving major construction projects in the Yunnan-Tibet region.  Academician Manchao He, director of the State Key Laboratory for Geomechanics & Deep Underground Engineering, proposed a new theory of excavation compensation method applied to the stability control of deep surrounding rocks, independently developed new NPR materials to support the excavation compensation method, and proposed high-stress NPR anchor cable excavation compensation support technology, and proposed new theories, new materials and new technologies for the prevention and control of large deformation of soft rock from the three levels of "Tao Tool Method". It has been widely used in major national projects such as mining engineering, tunnel engineering, water conservancy project, protection engineering, slope engineering, cultural relic protection engineering and earthquake engineering and so on, and these results have achieved significant safety, social, and economic benefits, leading and promoting technological progress in related industries.