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Shanghai is slowly sinking
Shanghai, the largest city in China and literally meaning “above the sea,” may soon become “under the sea” if growth is not managed, experts say.
Rapid economic growth in Shanghai over the last two decades has resulted in growth expansion of skyscrapers in many areas of the city. These buildings have added a significant burden to the soil and bedrock, to the extent that the ground has been sinking. On average, the city is sinking at the annual rate of 1.5 cm (0.7 inch). The sinking ground has already affected the construction of subways and high-rises. Shanghai may become an underground city in 50 years if the current situation continues.
The Yangcheng Evening News reported that the problem is most severe in Pudong District, where a mere 540 square km (208 square miles) of land is home to 1.4 million people. In the financial district, where there is large concentration of skyscrapers,the ground is sinking at 3 cm per year, doubling the city’s average. In the area near the 420-meter tall Jinmao Tower, which once was the tallest building in the world, ground is sinking at 6.3 cm every year.
Shanghai Water Resources Bureau staff attributes ground sinking to weight from the construction of skyscrapers, excavation for underground projects such as the subway system, and the over consumption of groundwater.
There are over 3000 buildings higher than 24 stories in Shanghai, while another 3000 are planned or under construction.
Experts say that global warming has resulted in a worldwide rise in sea levels. By 2050, the water level near Shanghai is expected to rise 5 to 7 cm, bringing even more pressure to the soil.
On July 1, 2003, a severe water leakage in the Fourth Line of the Shanghai subway led to the leaning and collapse of several high-rises nearby, sending a sobering warning to building officials.
Furthermore, the varying speed of ground sinking in different areas could potentially threaten the stability of the subway tunnels.
However, these warning signs have not discouraged the city and eager developers. The Yangcheng Evening News reported that another skyscraper project, vying to become the world’s tallest, is planned in Pudong’s financial district near the Jinmao Tower. The estimated cost for the new 101-story building is $625 million.
Chinese geologists say that Shanghai was originally a shoal, and its foundation is composed of sand and silt washed over by the Yangtze River. The top layer of the city is 300 meters of soft soil, which is water-absorbent, permeable, and elastic like a sponge.
Building records show that by the 1960s, there were 40 high-rises in Shanghai. During the 1980s, 650 new high-rises were built. Two thousand new high-rises were built in the next decade. The construction industry was especially robust in 1997, when 484 buildings were completed. Currently there are over 3000 high-rises of more than 24 stories in Shanghai, more than 100 of which have 100 or more stories.
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