| As one of the biggest cities,a very important economic center and the most developedport around the Bohai Sea, Tianjin has been suffered by land subsidence since 1970's . Landsubsidence was found in 1923 with the history datas of bench marks, the sedimentation ratewas very small ,only millimeters in the initial, the speed was increasing along with thetime.The phenomenon of land subsidence was severity by 1986,the speed was slowded afterthe group of land subsidence founding in the year. There are four phases in the history: theinitial time in 1923—1957;the land subsidence centers were come being in 1958—1966;therapid developing time in 1966—1985;the preventing time from 1986 to now.Land subsidence has occurred in all plains on the south of Chengguan Town and BaodiCounty, covering about 8000 km2. Areas in the south and in shore are the most serious.There are five old land subsidence centers as Tianjin city, Tanggu District, Hangu District,Dagang District and Industrial Zone in the down reaches of Haihe River.Over withdrawal of groundwater is the primary reason,and the process of the landsubsidence forming is consistent with the groudwater drawing. The mechanics of the landsubsidence is that pumping large quantity of groundwater makes the water table fall so thatpore pressure decrease and the effective pressure increases which brings soil compressionand land subsidence is expressed on the surface in sequent. In addition, the landsubsidence isincapable of resuming, by reason of the especial geological setting.Forecasting the land subsidence in 2001—2010 with the history datas of bench marks in1986—2001.As a result, the accumulative land subsidence is very large, the new landsubsidence centers coming into being, but the speed of land subsidence is slowing.Land subsidence belongs to an important type of geological disaster and gives arestrictive impact on the development of the city. So some effective measures need to betaken to prevent and mitigate the land subsidence in the future.
|
PDF Full Text Request