| Land subsidence,as a slowly changing and irreversible environmental geological disaster,seriously affects the coordinated development of regional construction planning,economy,en-vironment and society.Since the 1920s,land subsidence has attracted more and more world-wide attention.By 2015,serious land subsidence disasters had occurred in 24 cities in 9 prov-inces,covering an area of 5860 km~2.Zhengzhou is located in the southwest edge of land sub-sidence area in North China Plain,and is one of the earliest cities to exploit and utilize ground-water.Long-term excessive exploitation of groundwater has caused land subsidence in the study area,has a significant impact on the structural safety of buildings and infrastructure,and is accompanied by ground fissure disasters,which seriously endangers the construction and oper-ation of linear projects such as high-speed railways and subways.Land subsidence has become one of the important factors affecting the urban planning and construction of Zhengzhou City and the sustainable development of regional economy.In this paper,on the basis of previous research work,the land subsidence investigation and soil mechanics test are carried out.The numerical simulation of land subsidence caused by groundwater exploitation in the key subsidence area of northern Zhengzhou is carried out,and the latest distribution characteristics of land subsidence in Zhengzhou are obtained by using time series InSAR technology.The main research contents and results are summarized as fol-lows:(1)Through drilling and sampling the strata within 100 m in the historical serious area of land subsidence,and indoor geotechnical test of the samples.The research results show that the serious subsidence area is from northwest to east.The lithology of strata above 100 m gradually transits from sand,silt and silty clay interbed to sand.The number of layers and overall thick-ness of clay layer gradually decreases.A large number of Quaternary loose strata are the mate-rial basis for land subsidence in this area.(2)Through the analysis of physical and mechanical parameters of each borehole soil sam-ple,it can be seen that each physical index of soil sample has a certain correlation with the increase of burial depth,and there is a significant correlation between each physical quantity.Both the deformation and compression coefficient of soil samples show the law of first increase and then decrease with the increase of pressure load.The deformation of soil samples with smaller burial depth under the same pressure is significantly greater than that of soil samples with larger burial depth;The soil sample with large buried depth has small rebound after un-loading,and there is permanent deformation;The compression coefficient appears inflection point at 100?200 k Pa,and is basically stable after 1600 k Pa.(3)Taking the serious land subsidence area where the four boreholes are located as the research object,using the groundwater level data near the boreholes and the land subsidence monitoring data,based on the Boit consolidation theory and the modified Cambridge model,the two-dimensional fluid-solid coupling model of land subsidence is established by using ABAQUS software,and the numerical simulation of land subsidence induced by groundwater exploitation is studied.The results show that the ground subsidence caused by the decline of shallow groundwater level in the study area,the settlement of the shallow soil layer above 30m accounts for more than 80%of the total settlement,which is the main contribution layer of ground subsidence.Under the condition of stable amplitude of groundwater level,clayey soil shows significant hysteresis characteristics;With the rise of groundwater level,the sand layer can basically recover to the original settlement.In addition to elastic deformation,the clay layer also contains large plastic deformation and residual deformation.(4)Using the free distribution of Sentinel-1A satellite data covering the urban area of Zhengzhou City from 2017 to 2021 by ESA,the data were processed by PS-InSAR and SBAS-InSAR techniques,and the latest land subsidence distribution characteristics in the study area were obtained.The results show that the deformation rate of most areas in Zhengzhou City is-10?10 mm/year,and the central part is a relatively stable area,which has a gradual upward trend.There are three obvious subsidence areas,which are located in the A area in the north of the study area,the B area in the east and the C area in the south,respectively.It is the latest development of land subsidence area in Zhengzhou City.(5)Area A is located in the area surrounded by Jiangshan Road-North Fourth Ring-Cul-tural North Road-Yingcai Street,Huiji District,Zhengzhou City.The most serious settlement area is located near Chenzhai Flower Double Bridge Base,Huiji District,Zhengzhou City.The maximum settlement rate is-22.52mm/year,and the cumulative settlement reaches 99.13mm.Area B is located in the area of East Fourth Ring of Zhengzhou City-Jinshui East Road-Qi-ancheng Avenue-Shangdu Road.The most serious settlement area is located near Xiaoyin-zhuang Village and Kangzhuang Village in Jinshui District of Zhengzhou City.The maximum settlement rate is-40.35 mm/year,and the cumulative settlement reaches 137.29mm.Area C is located at the junction of southern Erqi District of Zhengzhou City and Xinzheng City.The most serious settlement area is located near Houzhuang Village of Xinzheng City.The maxi-mum settlement rate is-19.27mm/year,and the cumulative settlement reaches 66.06mm.(6)According to the indoor soil test,numerical simulation analysis and InSAR monitoring results,the formation mechanism of land subsidence in Zhengzhou City was preliminarily de-termined.The lithology and distribution characteristics of stratum in Zhengzhou City are the important geological foundation conditions for land subsidence in Zhengzhou City.Mining groundwater and urban engineering construction are the main causes of land subsidence in the study area.With the implementation of shut-in pressure mining in Zhengzhou City,the land subsidence caused by mining groundwater is gradually decreasing.The land subsidence caused by engineering construction will become the main cause of land subsidence development in Zhengzhou City.The research work on land subsidence in Zhengzhou City has certain reference value for the prevention and control of land subsidence disasters in Zhengzhou City,and has certain ref-erence significance for the scientific planning and construction of Zhengzhou City. |
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