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Northwich: a town with a sinking experience

  The miscalculation of rock salt mine engineers 200 years ago almost sounded the death knell for the market town of Northwich in Cheshire, England, but an unusual rescue plan in recent years has finally saved the town from sinking and bringing it wealth. The Doom of the Underground Salt Mine Hole…
  ”Northwich is like a dream town where everything seems to be in a state of madness, with streets stretching out at odd angles and houses like drunken It seems to be leaning forward, and when I enter the library to read, it feels like I am on the deck of a ship with high winds and waves, and I feel dizzy when I walk around, and it seems that there is a possibility of hitting the wall at any time.”
  This is not a The drunken nonsense of a drunken man, but a report written by a newspaper reporter a hundred years ago after investigating and interviewing the anecdote of the town of Northwich, Cheshire, England, influenced and made it an “upside-down chaos” in the continuous decline. “The town is the result of the historic local rock salt mining.
  Today, the town of 20,000 people is largely back to normal, and houses are no longer tossed around, which is the result of a £32 million “ground stabilization project” in recent years, a massive project to mine rock salt in the city centre More than 1 million tons of cement slurry were poured into the four huge cavities left.
  
  ●The town sinks ●
  
  In the 19th century, the rock salt mines brought prosperity and employment opportunities to the Northwich people, and the town’s population ballooned from less than 1,500 to 15,000. However, rock salt mining has also taken a heavy toll on the town, creating huge holes in the ground that could collapse at any time. Back then, it was common for shops, houses and even entire streets to cave in. In fact, the peculiar view of Northwich’s sloping houses with “bends and backs” attracted many foreign tourists, and throughout the Victorian era, there was a steady stream of visitors who wanted to see this rare spectacle for themselves.
  A resident who lived here in the early 20th century described the feeling of the houses sinking, saying, “They don’t sink all at once, but a slow gradual process, and when we think the sinking is too much, we use hydraulic jacks. Lifting it up, I heard that some people have to prepare a saw before going to bed, because they are afraid that if they wake up in the morning and find that the door cannot be opened, they can use the saw to break through the door.”
  There is also a small The girl, a shop in her family sank two meters below the road, this situation made her very confused, she complained, “Nothing can hang on the wall, they always go to the corner where they shouldn’t be. Go, I don’t know when our house will sink into the ground.”
  In order to deal with the problem of the subsidence of the ground, people have conceived a unique architectural form, the whole building is built in a wooden frame, if the ground It sank, managed to get the roof up, and even moved the whole house to another place, Northwich’s unique architectural style can still be seen in this town today.
  
  ●Miscalculation ●
  
  Since Roman times, people have been mining salt underground in Cheshire, England. In 1779, a very pure rock salt deposit was discovered deep underground in Northwich. Road, and Northwich’s troubles began at this point.
  The mining engineers at that time deliberately left some large salt pillars unused to support the top layer of the salt pit. According to their calculations, they believed that the salt pillars, which accounted for 8% of the total ground area of ​​the salt mine, were sufficient to support the top surface. It turned out that their estimate was a major blunder.
  When the salt is excavated, water begins to infiltrate to fill the hollowed-out space, and the salt dissolves in the water. Stable. Problems began to arise in the 19th century. In the face of fierce competition, miners flushed some old salt mines with water and pumped the brine to the surface. The ground above the cave began to become unstable.
  In 1880, this practice had catastrophic consequences. The underground salt mines were interconnected. If a shaft slipped, it often affected a large area. By December 6th of that year, a sudden collapse caused a sensation. , which was called the “Great Sinking Event” at the time.
  The violent activity of underground mud and water has had a series of consequences. The Weaver River has flowed backwards, houses and buildings have collapsed, roads have been destroyed, underground gas and water have been flushed out of the ground, causing mud volcanoes to erupt, and some salt factories and chimneys have even been submerged. .
  Although the subsequent ground subsidence events were not as intense and sensational as they were at the beginning, they also brought disaster and pain to the people living here. Some people lost their homes and livelihoods. Between 1880 and 1920, the subsidence of the ground affected the sewage and drainage pipeline system, and the local government had to raise the pavement of the street several times, which not only cost the government a lot of financial resources, but also brought great trouble to some residents and shopkeepers, because They found that the ground floor of their house was two and a half meters below the street level!
  
  ● Rescue plan ●
  
  Four large salt mines formerly mined in Northwich left dangerous hidden dangers, and the seriousness of the problem was fully exposed in 1988, when a real estate developer planned to expand the city center northward, and engineers in Several test holes were drilled in the ground, and it was found that some of the salt pillars supporting the ground were extremely unstable, and all major development projects in Northwich were immediately halted.
  In the middle of the 20th century, relevant departments conducted a comprehensive investigation of the situation of underground salt mines. People drilled holes on the ground to determine the strength of the underground salt column, installed highly sensitive deformation measuring devices everywhere, and used relevant The instrument measures ground movement. The relevant survey report concluded that there was a high probability of the mine collapsing and that measures had to be taken.
  Weaver Valley MP Mike Hall, determined to find solutions for Northwell’s future security, said in a tour of government ministers, “If no action is taken, Northwell’s environmental catastrophe will be in our sights. Happening in the hands, according to the research, the city centre of Northwell is going to collapse in the next 5 to 10 years, we have no choice and if we don’t act, Northwell will be a big hole.”
  In 2002, the English Partnerships, the UK’s national urban regeneration agency, allocated £28.9 million to the Northwell Salt Mine Reinforcement Project to study a material formula for filling four Northwell rock salt waste mines. The material must have a certain fluidity and can flow into the underground salt mine through a pipeline as long as 2.5 kilometers from the mixing equipment, but it must be able to quickly condense into a solid after being pumped into the ground.
  About 780,000 cubic meters of space would need to be filled in the waste salt mine, the equivalent of 290 Olympic swimming pools, and the amount of material needed to stabilize the project was astonishingly high, requiring a total of 1.3 million tons of cement slurry. The filling works began in January 2005 and were completed in November last year, ending Northwich’s history of subsidence and paving the way for the town’s future development.
  In fact, people have no doubt about the stability of these abandoned salt mines. The huge space left after rock salt mining is used as waste disposal landfill, and some are even considered as an ideal place to preserve archives. land. There are currently 800,000 filing cabinets with various documents stored in the underground salt mine cavity, including documents from the British Parliament and health authorities, some precious national archives, and even precious materials from the Oxford University Library. Books etc.
  The story of bright and white salt, which is indispensable in daily life, has become an important page in the history of Cheshire, England. It is the source of wealth in this area, and it has also brought great trouble to people in this area. Today, rock salt mining remains a major source of revenue in Cheshire, England, but the people of Northwich are relieved that they no longer have to worry about the danger of the ground sinking as water seeps into the ground.

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