China-Laos railway tunnel Photo:Xinhua

China-Laos railway tunnels' construction has been continuing to make breakthroughs, as one more major tunnel was drilled through on Friday in the tropical mountains of northern Laos.

Chinese railway engineering company, namely China Railway No. 8 Engineering Group (CREC-8) on Friday bored Ban Ka No. 1 Tunnel near the ancient Lao capital of Luang Prabang, some 220 km north of capital Vientiane. This marks another important milestone in the tunnel construction of the China-Laos railway, as, with a length of 4,585 meters, it is the second longest tunnel on the rarely-inhabited peninsula half-circled by the Mekong River in northern Luang Prabang.

The poor transportation infrastructure, without bridges connecting to other areas of Luang Prabang and roads in the area, the living and production conditions on the peninsula have been quite hard.

What's more, the Ban Ka No. 1 Tunnel has to pass through unfavorable geology, and it is listed as a high-risk, difficult and bottle-neck project for the China-Laos railway construction.

The surrounding rocks of the tunnel are not strong and tend to get broken easily, while the rock formation where the tunnel goes through is complex and variable, with many karst sections and faults. High geothermal heat and high stress around, the tunnel is extremely easy to meet deformation and collapse during construction.

During construction, hydraulic discharge and mud cleaning have also brought difficulties to the Chinese engineers.

However, with efforts made by the Chinese and Lao sides, the tunnel's construction was carried out scientifically, and rapidly. In last May, the CREC-8 once achieved the first place along the railway with over 1,000 meters bored into a tunnel from a single working face in the Ban Ka No. 1 Tunnel, which laid the foundation for its Friday completion.

The China-Laos Railway is a strategic docking project between the China-proposed Belt and Road Initiative and Laos' strategy to convert from a landlocked country to a land-linked hub.

The 414.332-km railway, with 198-km tunnels and 62-km bridges, will run from Boten border gate in northern Laos, bordering China, to Vientiane with an operating speed of 160 km per hour.

The electrified passenger and cargo railway is built with the full application of Chinese management and technical standards.

The project started in December 2016 and is scheduled to be completed and opened to traffic in December 2021.