Chinese engineers digging world’s longest tunnel in Xinjiang desert hit a wall – of gushing water
- Work on tunnels to introduce snowmelt to arid region disrupted several times by ‘water inrush accidents’, paper by project engineers says
- Apart from the risk of damage to costly boring machines, such incidents threaten to seriously affect construction schedule
Chinese workers building what would be the world’s longest tunnel have come up against an unexpected problem in one of the driest areas on Earth – gushing streams of water.
“High groundwater levels have caused frequent water inrush accidents that seriously affected the construction schedule,” said Deng Mingjiang, a professor with the Chinese Academy of Engineering, in a paper published in domestic peer-reviewed journal Tunnel Construction last month.
Kashuang tunnel, the longest of the three mega tunnels in the project, is expected to stretch for 280km (174 miles), more than twice as long as the Delaware Aqueduct – the main water supply tunnel of New York City – which has held the record since 1945.
But from time to time, the tunnel boring machines (TBMs) run into an unusually rich groundwater source that bursts out so forcefully that it could fill a swimming pool in an hour.
Every time the flooding alarm flashed red, the report said, workers would need to evacuate and the giant boring machine would be made to stop and pull back immediately or risk serious damage.
The frequent setbacks had threatened the safety of everyone on site, the paper said.
China’s increasing use of Irtysh water has irked its two neighbouring countries.
These include hydropower plants and irrigation infrastructure for the entire Irtysh river basin, home to about 15 million people across the three nations and with good potential for economic development.
Authorities in Russia and Kazakhstan did not respond to the Post’s request for comment.
A tunnelling project usually involves one or two TBMs. Also known as “moles”, such machines represent one of the largest robotic devices in existence, with each costing tens of millions of US dollars.
The rotating blades of the machines can cut through nearly all types of hard rock, with onboard sensors adjusting operations automatically.
The Xinjiang water supply project had 20 moles working at different sites at the same time. Even in China, where large-scale infrastructure-building is the norm, such a fleet was a “rare sight to behold”, Deng and his colleagues said in their paper.
However, unlike other major infrastructure projects in China, news on the Xinjiang tunnel has not appeared in any state media. Its route remains classified, and no official deadline has been announced.
Chinese scientists say model can predict dangerous waves in Andaman Sea
By the end of June, two years since starting construction, nearly 60 per cent of tunnel works had been completed, according to the engineers.
However, the frequent flooding could cause serious delays. A 10km tunnel for India’s northern Dul Hasti hydropower station, for instance, took 12 years to build – in part because of gushing water, according to Deng.
Not only are geological conditions in Xinjiang’s deserts extremely complex, nearly half the estimates arrived at via geological surveys in the route-planning stage turned out to be wrong, according to the paper.
But the engineers came up with some new methods to deal with the unprecedented challenge.
Traditional ground penetrating radars can detect the presence of water in advance, but they work only when the tunnel boring machines stop.
Deng’s team and their collaborators have developed a new type of seismic detector that can be mounted on the TBM itself and uses vibrations to detect water and other impediments behind the rocks.
So the tunnelling team was usually prepared when a leak occurred, activating a pump to drain the water out of the tunnel, after which another team would seal the leak.
How deadly floods in western China could threaten new Silk Road
But the mole could not move forward at all until the engineers had identified the precise source and volume of the water and found a way to divert the flow away from the tunnel, the paper from Deng and his team said.
It remains unclear how much water the tunnel would drain out from the Irtysh river.
But the second-largest river in Xinjiang could provide more than 11 billion cubic metres (2.9 trillion gallons) of snowmelt a year, according to official data.
Going by average water consumption levels in China, this amount would meet the needs of more than 20 million people, or the entire population of Xinjiang.
Xinjiang is China’s largest provincial region, and more than 60 per cent of it is covered by the Gobi and other deserts. Urumqi, the regional capital, is further from the oceans than any other city worldwide.
Researchers have also found that many deserts in Xinjiang used to be lakes, some of which existed until the emergence of the ancient Silk Road about 2,000 years ago.
According to their estimates, the volume of water under the Tarim basin alone could be as big as all five Great Lakes in North America combined.