Workers deal with gushing water during the construction of the Dazhushan Tunnel on the Dali-Ruili Railway project in May.Provided To China Daily
When work began on the Dazhushan Tunnel, the plan was to finish it in five years. That was in 2008 - and construction crews are still digging.
Unexpected difficulties mean the 14.5-kilometer tunnel, a critical juncture on the Dali-Ruili Railway in Yunnan province, is now scheduled for completion in 2021, Xinhua News Agency reported.
The tunnel runs through six faults in the Hengduan Mountains on the Qinghai-Tibet Plateau. It would have been beyond imagination to build on the earth fractures 20 years ago, said You Hongsheng, a spokesman for No 4 Company of China Railway First Group Co, which is digging the tunnel.
In August 2009, immediately after the first drilling began at one of the six fault lines, a 20-centimeter crack appeared in the operating face. The crack continued to widen as mudrock gushed out, filling a space 200 meters long and 6 meters high in about five hours.
"We failed to predict the fragility of the fault," said Jiang Dong, a construction manager at the site. "It is just like drilling into a piece of bean curd. The mudrock started to flow into the tunnel as we worked."
Jiang said the problem was later solved by building a wall to stop the mudrock flow and grouting the flow until it became solid. "Then we dug through the solid part to carry on with the project."