Ground Subsidence in Shanghai

[ashjun]

The ground subsidence at Shanghai (about 11-15mm/year) has been related to the number of high-rise buildings that have come up in the city.
If that is the case, then is the ground failing?

Or otherwise, is it related to the large scale water extraction?
Is there any expert from that area who can throw some light? and the counter-action measures that are adopted?

Rgds

 

[BigH]

Sounds to me as it could be a case of Bangkok - water extraction on a large scale lowering the groundwater level in the normally consolidated clay soils - then this adding more effective pressure within the clay leading to additional consolidation. Not sure of the soils in Shanghai - can you enlighten us?

 

[ashjun]

I am not sure either, read a news item in the bbc archive; the reason given was because of massive skyscaper construction over the last decade or so.

 

[Mccoy]

Mmmmm,
I cannot say anything about Shangai, but the topic reminds me of the weird situation which happened in Milan, the Italian city with the highest concentration of industries.
The massive groundwater extraction, started in the post war years, caused a generalized depression of the piezometric level underneath the metropolitan area, and triggered subsidence phenomena (not very serious, subsoil is mostly fluvio-glacial sequences of sand & gravel).
Since 1990, the slump in global and national economy caused many plants to shut down. As a consequence, the water table went back upward, and flooded the underground parking basements of a few buildings, built when the water table was deep, and evidently nobody thought about a possible reversal of the situation.
It was pretty impressive to see images of people exploring such parking basements by inflatable dyngies and speleological equipment!

 

[BigH]

Foresight! - not a typical happening; that of reversal.

 

[Mccoy]

Well,
it would appear that ole Mr. Overpumping would be responsible for ground subsidence in Shanghai as well, as the following excerpt goes; it makes perfect sense, if we just look up at he the GNP incremental figures in China, reliable index of (humongous) industrial development.

From

http://eces.org/articles/000568.php

Survey finds large areas of China, including 46 cities, are experiencing alarming rates of ground subsidence due to the overpumping of groundwater supplies, posing a serious threat to buildings and people's lives and causing huge economic losses.
Parts of China are rapidly sinking due to the overpumping of groundwater supplies, People's Daily reports. According to a survey conducted by the Ministry of Land and Resources, the rapid depletion of groundwater has produced more than 100 massive tunnels covering a total area of 150,000 square kilometres across the country. The cities of Shanghai, Tianjin and Taiyuan report the worst sinking, each of them having dropped by more than two metres since the early 1900s.

 

[Mccoy]

Sorry,
I realized there is no reference to the source, which seems nevertheless reliable.
If anyone is interested, a simple web search turns out pretty interesting material (by surely reliable sources such as Daily China and more)