Jinyang Tunnel, the Longest on Xichang–Zhaotong Motorway, Breaks Through

According to China Railway Group Limited, the full breakthrough of Jinyang Tunnel was achieved on 20 October. The tunnel forms part of the Xichang–Zhaotong motorway, invested and developed by China Railway Urban Investment Group under China Railway Group and constructed by China Railway Tunnel Group.

Lying in Jinyang County within the Daliang Mountains, on the border between Sichuan and Yunnan provinces, Jinyang Tunnel stretches for 12,180 metres. It adopts a separated twin-bore layout, with a maximum overburden depth of 1,723 metres. The route passes through 27 strata sequences, 43 lithological contact zones and multiple fault zones, presenting highly variable geological conditions. Abundant groundwater was encountered throughout construction, with a total volume of 160 million cubic metres of water inflow recorded and a maximum hydrostatic pressure of 3.5 megapascals.

To tackle the complex construction challenges, the project team established an industry-university-research collaborative platform together with an academic team of academicians. A full-cycle risk control framework was put in place, integrating advance geological forecasting, intelligent monitoring and measurement, graded support and dynamic grouting. Multiple exploratory boreholes were deployed in water-rich high-pressure sections to release water and reduce pressure actively. 

For zones with phyllite, sandy dolomite and soft rock prone to large deformation, the design balanced flexible pressure relief and rigid bearing capacity of surrounding rock, lifting tunnelling efficiency by 30 per cent. 

In sections vulnerable to rock bursts, the team adopted active energy release measures including face water sprinkling, advance stress-relief boreholes and high-pressure water injection softening. Combined with smooth blasting and short round lengths, the approach curbed the build-up of strain energy.

Once open to traffic, the Xichang–Zhaotong motorway will connect with the G5 Beijing–Kunming motorway, G4261 Rongli motorway and S7 Chenghui motorway. It will strengthen links between the Chengdu Economic Zone, Southern Sichuan Economic Zone and Panxi Economic Zone. The scheme removes a transport bottleneck at the junction of Yunnan, Guizhou and Sichuan provinces, reinforces the national motorway framework in south-west China and supports rural revitalisation in the region.