The Dajian mountain and Taida village tunnels of the Yuxi-Mohan section in Southwest China's Yunnan province, both key sections of the China-Laos Railway, were dug through on Aug 31.
The tunnels were the last two to be completed among the six contracted by China Railway 18th Bureau Group Co., Ltd., a subsidiary of China Railway Construction Corporation Limited (CRCC).
Located in Pu'er in Yunnan, the 14.2-kilometer Dajian mountain tunnel goes through three faults and has two shallow sections.
The weak surrounding rock with fragile rock mass becomes soft and swelling, resulting in frequent water gushing. It was recorded that the largest daily volume of water reached 52,000 cubic meters, equaling that of 23 standard swimming pools.
The condition added to the difficulties of engineering and the construction risks.
To guarantee on-schedule progress the engineering team worked on 10 underground surfaces at the same time.
As for the Taida village tunnel, it is only 5.8 kilometers but was dug through various kinds of poor geological landforms including landslide masses, shadow sections and faults.
The toughest part was the 180-meter water-rich silty-fine sand layer which has extremely bad auto-stability. The layer filled with slurry whenever water flowed in, making the digging extremely challenging.
Several supporting and protective measures including curtain grouting in the cave and longhole grouting of the land surface were taken to ensure quick and safe engineering, which also helped set a record for similar tunnel construction in China.
According to CRCC, the 1,000-kilometer China-Laos Railway is a major traffic infrastructure of the Belt and Road Initiative.
Once operable, it will take passengers only three hours to travel between Kunming and Jinghong in Yunnan and about 12 hours to go from Kunming to Vientiane, capital of Laos.
A view of the Nasu River Bridge that links the Dajian Mountain tunnel and the Taida village tunnel [Photo/sasac.gov.cn]
(Executive editor: Wang Ruoting)