The Study On Acting Factors And Systemic Control Of Land Subsidence In Shanghai

Land subsidence is quite universal around the world, especially in urbanized area. With the acceleration of industrialization and urbanization, economic and engineering activity is becoming the crucial key factor in the land subsidence process. Land subsidence has been an environmental geologic problem and one of important urban geologic hazards, which has been caused great attention of international academia and governments.This paper expounded the formation and development roundly of the land subsidence in Shanghai, and gave a systemic analysis of the restrictive and acting factors as well as its influence in the land subsidence process. On the basis of it, countermeasure and suggestions were proposed.By the breakthrough point of new evolution situation in recent years in Shanghai, this paper made a full endo-exoteric analysis and expatiation of land subsidence acting factors. On the side of internal cause, geological backgrounds such as regional structure and depositional environments of Yangtze estuary, distribution of Quaternary stratum and evolvement characteristics were analyzed, consolidation and distortion of Quaternary stratum which resulted in land subsidence was evaluated through the way of aquifer stress-distortion relation, mild clay microstructure and its effect and representation in water-soil two phase system, distortion characteristics of fresh sediment caused by tidal flat filling-up acceleration, dredger fill and so on. From the aspect of external cause, it was spread by the view of groundwater exploitation pattern and its effect on exploitation to the adjacent provinces, urban engineering construction influence, and so on. According to the superposition of land subsidence relative to sea level rise, the effect of land subsidence on urban flood prevention security, the function and influence of land subsidence in urban disaster system, ecological effect of land subsidence was explored. Guided by scientific outlook on development, how to harmonize economic-social development, natural resource exploitation and protection of geological-ecological environment were discussed, readjustment and control countermeasure of land subsidence system was put forward in order to the promotion of land subsidence geological hazards and deepen its prevention and cure as well.Compared with previously research, breakthrough and innovation of this paper are as follows: structure characteristics of continually compressing soft clay were analyzed from the microcosmic view; internal mechanism of distortion was parsed from the view of solid-liquid water and soil two-phase system; defined "engineering land subsidence" as a new type of subsidence; from the aspect of utilization of underground space such as dense architectural complex and high-rise buildings, construction and operation of underground railway and tunnels, excavation of deep foundation ditch, combined with engineering practice and monitoring data, characteristic and law of engineering land subsidence was expounded; rational consideration aiming at the prevention and cure of land subsidence was made; primary and secondary contradiction and their conversion during the process of land subsidence was analyzed dialectically; new change since the previously subsidence control measure implemented was described when new thought of land subsidence prevention and cure combined flexible adjustment with rigid control was proposed, which means dynamic adjustment and control will be executed by setting the threshold of annual sedimentation velocity and gross under the premise of geological environment capacity and urban recovery faculty. When land subsidence is forecasted scientifically and under control effectively, general control object of land subsidence will be realized and the external demand of underground water, land resource for economic development can be met according to yearly, regional and different lays adjustment.