Analysis Of Ground Subsidence Patterns And Causes In Zhengzhou City Based On InSAR Technology

Land subsidence is one of the main geological disasters restricting the sustainable development of society and economy,which can continue to cause damage to urban infrastructure,rail transit,and underground pipelines.Zhengzhou,as a national central city,has become one of the threats to urban security and urban development due to the exploitation of groundwater and the continuous expansion of urban areas in recent years.In this paper,the InSAR technology is used to obtain the surface deformation information of Zhengzhou City,and combined with the groundwater level change,urban construction,regional geological structure and rock and soil mass in the study area,the land subsidence law,genesis and subsidence trend of Zhengzhou City are analyzed.The main research conclusions are as follows:(1)From January 2018 to July 2019,the InSAR monitoring covered an area of 1050km2,the land subsidence area was about 951.66 km2,accounting for about 90.63%,and the average annual subsidence rate was 4.64 mm/a.There is no obvious falling funnel in the study area.Overall,the areas with subsidence greater than 20 mm are mostly located in the newly expanded urban area and areas with dense new buildings,mainly in the northern part of Huiji District,near Beilong Lake,Guancheng District,and the second area.The eastern area of the seven districts has a total area of about 121.66 km2,accounting for 11.58% of the monitoring coverage area.(2)During the monitoring period,the main urban area of the study area was in a state of continuous uplift as a whole,and the cumulative amount of uplift was between 0 and38mm;the northern and eastern regions were in a state of continuous subsidence,and the cumulative amount of subsidence was-10～-65 mm,of which,During the monitoring period of Beilong Lake,due to the influence of nearby construction,serious land subsidence occurred in this area.As of July 2019,the cumulative amount of subsidence reached-98.34mm;since October 2018,the western area has gradually changed from a subsidence state.In the uplifted state,the accumulated amount of settlement increased from-80 mm to-34 mm.(3)Through the correlation analysis between the groundwater level in the study area and the land subsidence near the corresponding point,it is obtained that during the monitoring time,the correlation coefficients of the two observation holes for the shallow groundwater level are 0.639 and 0.740,respectively,and the two levels of the middle and deep groundwater levels are 0.639 and 0.740 respectively.The correlation coefficients of the observation holes were 0.870 and 0.799,respectively,and the correlation coefficients of the two observation holes of the deep groundwater levels were 0.392 and 0.215,respectively.The land subsidence in the study area is positively correlated with the change of groundwater level,and the correlation between land subsidence and middle and deep groundwater is stronger.(4)In the areas with subsidence greater than 20 mm in the study area,new urban built-up areas have appeared since 2016,indicating that the land subsidence of Zhengzhou is closely related to urban construction.The activity of the Laoyachen fault in the study area and the compaction of the Cenozoic strata will have a certain impact on the land subsidence in the area.(5)Combined with the analysis of the subsidence characteristic values and subsidence causes of Zhengzhou City obtained by leveling measurements over the years,it is concluded that the land subsidence trend of Zhengzhou City has slowed down on the whole,and the average annual subsidence has shown a downward trend.In the future,the subsidence trend of Zhengzhou City will be east to north.The reason for the development is due to the comprehensive influence of factors such as closure of wells in urban areas,groundwater pressure extraction,changes in urban water supply structure and urban expansion.