On March 9, 2021, the longest highway tunnel in Gansu Province, from No. 3 inclined shaft to exit section of Muzhailing tunnel of Weiwu expressway, with a total length of 15.2km, was through more than 1700 employees of China Railway 21 bureau group working hard and hard to work hard and through the safety, marking a major breakthrough in the construction technology of soft and weak surrounding rock in the world-class highland.

"It has opened an important barrier for the overall connection of Muzhailing tunnel and the early completion and opening of the whole line." Gansu dada road company, the construction unit, specially sent a congratulatory letter to the group, expressing thanks to all the builders for their united efforts, returning to work after the epidemic and persevering in fighting. More than 60 people, including the owner, designer, supervisor, adjacent bid section, project management personnel and representatives of work area, attended the opening ceremony.

Muzhailing super long tunnel crosses the watershed of Zhanghe River and Taohe River, and passes through the junction zone of several blocks. The highest altitude is 3252 meters, and the maximum buried depth is 629 meters. The strata through the tunnel are mainly carbonaceous slate. The rocks turn into sand when encountering wind and mud when encountering water. There are 12 large fault fracture zones in the strata, and the strata are strongly squeezed. All of them are Grade 5 surrounding rocks, belonging to extremely high stress area. The 11km section of Muzhailing double track constructed by the company is the section with the worst surrounding rock and the most difficult construction, which is equivalent to tunneling in tofu.

The large deformation of soft surrounding rock of Muzhailing tunnel affects the construction progress of the whole project. During the construction, it is revealed that the main rock stratum is carbonaceous phyllite, with broken rock mass, developed joints and fissures, thin-layer structure, and easy to soften when encountering water. During the construction, large deformation occurred many times. The pressure of 1 MPa is equivalent to the pressure of 100 meters water column within 1 square meter, and the maximum pressure of surrounding rock of Muzhailing tunnel is 38.38 MPa. But the pressure of gumuzhai tunnel is not the worst. The deformation of the tunnel in a single day can reach more than 100 mm. The arch frame is set up at the top of the tunnel, and it can be deformed and twisted into a twist shape in a few days.

In view of the complex and changeable geological conditions, high altitude, less vegetation, thin oxygen and other construction environment, the mechanical excavation, large arch foot construction technology, early strength and fast hardening sulphoaluminate cement grouting and other measures are adopted to control some conventional deformation, but it can not effectively deal with the treatment of large deformation section. Through unremitting efforts in all aspects, they introduced NPR anchor technology from academician he ManChao of Chinese Academy of Sciences, which effectively restrained tunnel deformation, ensured construction progress, and ensured construction quality and safety.

It is reported that the Muzhailing tunnel of Weiwu Expressway civil engineering section 7, which was constructed by the group, has been connected for four times. The 3803m connection from the No. 3 inclined shaft to the exit section has greatly changed the ventilation, drainage and traffic conditions in the tunnel, creating a good construction environment for speeding up the whole connection of Muzhailing tunnel.

Weiwu expressway is an important part of Lanzhou Haikou National Expressway (G75) in Gansu Province. It is the most convenient channel between Northwest China and southwest China. Muzhailing super long tunnel is the longest highway tunnel in the history of highway construction in Gansu so far, ranking in the forefront of the country. (please refer to www.seetao.com for reprint.  ）Video program director of seetao.com / Sun Mengmeng Later period / PEI Yongsheng