China’s effort to construct the world’s longest tunnel has hit hurdles as a result of high groundwater levels.
In a report published this month in the Chinese peer-reviewed journal Tunnel Construction, Deng Mingjiang, a professor with the Chinese Academy of Engineering (CAE), stated, “High groundwater levels have caused frequent water inrush accidents, which have adversely impacted the construction schedule.”
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The ambitious project aims to bring snowmelt from the Altai Mountains into the deserts of northern Xinjiang –one of the world’s driest locations — via 500km (310 miles) of deeply dug tunnels.
Of the three mega tunnels in the project, the Kashuang tunnel is the longest one, 280 kilometers long, which is more than twice as long as the Delaware Aqueduct, New York City’s major water supply tunnel. The New York tunnel has held the record of being the world’s longest tunnel since 1945.
However, the tunnel boring machines (TBMs) regularly come across an extraordinarily rich groundwater source that surges forth with such force that it might fill a swimming pool in an hour.
The CAE report further stated that whenever the flood warning light flashed red, workers would have to evacuate, and the massive boring machine would have to come to a halt and pull back promptly or risk significant damage.
The construction process was substantially hampered by these wet zones. The TBMs would only be able to advance 200 meters (660 feet) every month in a wet zone, which is about half the average rate in a dry region like Xinjiang.
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The Xinjiang project aims to divert water from the upper reaches of the Irtysh River, which originated in the Altai Mountains in China and flows north through Kazakhstan and Russia into the Arctic Sea.
China’s growing reliance on Irtysh water has reportedly upset its two neighbors. According to a Beijing-based researcher quoted by South China Morning Post, the three countries have kept the disagreement out of the public view, concentrating rather on certain collaborative infrastructure projects under China’s multi-nation Belt and Road Initiative.
The project includes hydropower plants and irrigation infrastructure for the whole Irtysh river basin, which is home to over 15 million people in three countries and has significant economic development potential.
These projects necessitate the use of large machinery, one or two TBMs are commonly used in a tunneling project. These machines, often referred to as “moles”, are among the world’s largest robotic devices, costing tens of millions of dollars each.
The machines’ revolving blades can cut through practically any sort of hard rock, and integrated sensors automatically modify operations.
Twenty moles reportedly operated at different areas in the Xinjiang water supply project at the same time. Even in China, where large-scale infrastructure construction is common, such a fleet was a “rare sight to behold”, according to Deng and his colleagues.
However, there has been little mention of the Xinjiang tunnel in state media. Its course is yet unknown, and no formal timeframe has been set. According to the experts, approximately 60% of tunnel work had been finished by the end of June, two years after construction began. Flooding, on the other hand, might create significant delays.
Deng cited the Dul Hasti hydropower project in India’s Jammu and Kashmir, saying a 10km tunnel took 12 years to build, partly due to gushing water.
In 2017, SCMP reported that Chinese engineers are attempting to construct the world’s longest tunnel, a 1,000-kilometer one that will divert water from the Yarlung Tsangpo (which is known as the Brahmaputra in India) in Tibet near Arunachal Pradesh to the arid Xinjiang region. However, these reports were later refuted by the Chinese Foreign Ministry.
The geological conditions in Xinjiang’s deserts are not only complex, but roughly half of the route-planning estimations based on geological assessments turned out to be incorrect. However, the report mentioned that the engineers devised some novel approaches to deal with the unusual challenge.
Traditional ground penetrating radars can locate water in advance, but only when the tunnel boring equipment is stopped. The team, on the other side, has invented a new form of seismic detector that can be put on the TBM and detects water and other obstructions behind the rocks using vibrations.
When a leak occurred, the tunneling crew was generally ready by running a pump to drain the water from the tunnel, following which another team would seal the leak. According to the report, the mole couldn’t move forward at all until the engineers pinpointed the exact source and volume of the water and devised a means to divert the flow away from the tunnel. The amount of water that would be drained from the Irtysh river by the tunnel is unknown.
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According to official data, the second-largest river in Xinjiang could deliver more than 11 billion cubic meters (2.9 trillion gallons) of snowmelt per year. This proportion would cover the demands of more than 20 million people, or the existing population of Xinjiang, based on China’s typical water consumption levels.
The Gobi and adjacent deserts cover more than 60% of Xinjiang, which is China’s largest province territory. The regional capital, Urumqi, is farthest from the oceans than any other city on the planet. However, Chinese scientists have observed that the dry region is becoming warmer and wetter as a result of global warming.
In a recent study, they cautioned that large-scale infrastructure construction in the region could incur substantial losses if it does not account for climate change-related natural disasters like flash floods.
Many of the deserts in Xinjiang were formerly lakes, according to researchers, with some of them existing until the establishment of the ancient Silk Road some 2,000 years ago. In 2015, a group of Chinese researchers discovered geophysical data pointing to the existence of a huge reservoir of water beneath the deserts of Xinjiang.
According to their calculations, the volume of water beneath the Tarim basin might be equivalent to the combined volume of all five Great Lakes in North America.
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