The world’s most difficult railway project is taking shape in southwestern China. The line connecting Dali and border town Ruili in Yunnan province is the first to cut through the Hengduan mountains, traversing some of the world’s most complex geological and topographical terrain. Running along the country’s southwestern frontier for about 330 km, the railway is expected to boost China’s links with Southeast Asia. The line is being built in two sections: Dali to Baoshan, and Baoshan to Ruili, a county-level city that serves as a major border crossing with Myanmar. The first section broke ground in 2008 and was completed in 2022. The second half is now expected to be operational within five years.
Its completion will mark a milestone for global railway engineering. The 133 km Dali to Baoshan section takes only about an hour, but it took tens of thousands of workers 14 years to complete because of the complex terrain. By comparison, building a similar railway line across flat, geologically stable terrain would only take about three years. When the section entered operation in July 2022, its builder, China Railway Group described how challenging the project had been. The company said that the line passed through areas with steep mountains, deep valleys, intense tectonic activity and unstable, fractured rock formations. The construction had to avoid major fault zones and cross four large rivers. This required building numerous technically demanding bridges and tunnels to support the railway. In total, 34 bridges and 21 tunnels were constructed. The 14.4 km Dazhushan tunnel alone, which cuts through six geological fault lines, encountered “almost every major engineering risk associated with large-scale tunnel construction” and took 12 years to complete, according to the company.
One of the biggest challenges was massive groundwater inflows. Water gushing into the tunnels equalled the volume of 156,000 standard swimming pools, forcing workers to labor in submerged conditions for extended periods. Construction of the second section, from Baoshan to Ruili, began in 2015. Engineers are now tackling the project’s final and most formidable obstacle: the Gaoligong Mountain Rail Tunnel, a 34.5 km stretch poised to be the longest such tunnel in Asia.
Builders working 765 meters below the surface in the heart of the Hengduan mountains are contending with extreme geothermal heat, high-pressure water inflows, and fragile surrounding rock. On February 11, the China News Service reported that the tunnel – regarded as the “throat project” of the railway – had reached only around half of its planned progress after nine years of construction. However, work is expected to speed up following recent technical breakthroughs.
The Baoshan to Ruili section of the Dali-Ruili Railway was among “projects set to be completed and opened” during the five year plan period from 2026 to 2030. Gao Shangjie, Senior Engineer with a local transport bureau, told reporters last month that advances in tunneling technology had significantly improved construction speed. If all went to plan, the tunnel would be complete and operational by 2028. The railway will transform transport in Yunnan’s mountainous west, cutting travel time from the provincial capital Kunming to Ruili to 4½ hours – half the current nine. As a key section of the China-Myanmar international railway corridor, the Dali-Ruili line would also “open a more efficient route linking China with countries in South and Southeast Asia”, the South China Morning Post reports.
