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Tianjin is one of our municipalities , industrial and commercial development of the port city and economic center of the Bohai Sea region , began to receive attention from the seventies of the last century, subsidence hazard . Based on historical data of the level point , land subsidence phenomenon started from 1923 , when the settlement is still in the early stages , only a few millimeters of the initial settlement amount is small , after sedimentation rate and settling more and more serious , to take \measures , land subsidence mitigation, Tianjin settlement process is divided into four stages of development :1923 - 1957, an early stage ; 1958-1966 the subsidence center initially formed stage ; the 1966-1985 land subsidence dramatic last stage of development ; since 1986 comprehensive settlement governance stage . Currently , the vast plain to the south of the Baodi Chengguan District have different levels of ground subsidence, an area of ??more than 8,000 km2 , particularly evident in the southern and coastal regions . The formation of the five old settlement center in the urban areas , Tanggu District , Hangu and Dagang and lower reaches of the Haihe River Industrial Zone . The history of the development of Tianjin land subsidence and groundwater extraction is basically the same , mainly due to excessive extraction of groundwater is causing land subsidence . Because of the over-exploitation of groundwater , the water level dropped , the pore water pressure decreases , increasing effective stress , the soil starts to compress generate the settlement , is the the Land Subsidence main mechanism , coupled with special geological environment in Tianjin , Quaternary cohesive soil layer , the resulting non- elastic compression ( permanent compression ) , so even if the water level recovery increased ground is also no possibility of a rebound . 1986-2001 geoid the basis of the measurement data , 2001-2010 predicted subsidence , the cumulative settlement or large , and the formation of a new settlement center , but the sedimentation rate has slowed down , the total land subsidence The trend is slowing . Land subsidence in Tianjin has become the major geological disasters , restricting the continued development of the city , some serious impact to the entire city construction . It is necessary to take effective preventive measures , to slow the settling velocity , final control purposes .
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