Research On The Response Of Surface Deformation To Groundwater Change In Xi’an Based On InSAR

Since the 1970 s,due to rapid urban development and large-scale population growth,Xi’an City’s confined groundwater has been over-extracted for a long time,resulting in a continuous decline in groundwater levels and severe ground subsidence.Uneven ground subsidence not only affects the stability of buildings in Xi’an City and the safety of transportation facilities such as subways and bridges,but also damages infrastructure such as underground pipelines and drainage systems.Therefore,conducting long-term monitoring of ground subsidence in Xi’an City,clarifying its spatiotemporal evolution characteristics,and revealing the influence mechanism of changes in confined groundwater on ground subsidence are of great significance for the prevention and control of ground subsidence disasters in Xi’an City.At the same time,SBAS technology can not only provide high-resolution monitoring data with wide coverage but also overcome the problem of temporal and spatial decorrelation,enabling long-term and stable monitoring of surface deformation,which is beneficial for studying the spatiotemporal evolution characteristics of surface deformation.Therefore,based on SBAS technology,this paper monitors the surface deformation in Xi’an and analyzes its driving factors.At the same time,the response relationship of surface deformation to groundwater change and the estimation of aquifer parameters were analyzed in combination with confined groundwater.The main research results of this paper are as follows:(1)Based on the SBAS technology,the average deformation rates of four periods(2003-2005,2007-2010,2009-2010,and 2015-2022)were obtained for the ground deformation monitoring in Xi’an City.The results show that the ground subsidence mainly occurs in the southwest suburb of Xi’an City,forming three subsidence funnels centered at Yuhuazhai,the Electronic MALL,and San Yao Cun-Fengqiyuan.The overall subsidence rate and range show a slow-acceleration-slow trend,and there are obvious uplift signals in some areas such as the Big Wild Goose Pagoda and the Electronic City during 2015-2022.(2)The response relationship between surface deformation and confined groundwater change was analyzed.Due to the low vertical hydraulic conductivity of the weak permeable layer,there is a lag in the time of surface deformation in Xi’an.Therefore,the lag time of surface deformation in Xi’an was estimated and found to be within six months.And by correcting the estimated results for deformation time,it was found that there is good consistency between surface deformation and changes in confined groundwater in Xi’an,mainly caused by elastic compression/expansion of confined aquifer systems.Then,the seasonal deformation of the southwest suburb of Xi’an City from 2009 to 2021 was extracted based on harmonic functions.The results show that the amplitude of seasonal deformation is 1mm to 9mm,except for Yuhuazhai showing a trend of first increasing and then decreasing,other areas show a decreasing trend.The peak time of seasonal deformation in the subsidence center is concentrated in January to March,and the stable area is concentrated in July to September.(3)The elastic skeleton storativity of 38 confined monitoring wells in Xi’an City was estimated using the InSAR deformation monitoring results and water level observation data.The research found that the elastic skeleton storativity in Xi’an City mainly ranges from 0.005 to 0.01,and shows strong spatial variability,with the coefficient in the northwest region being significantly higher than in other regions.In addition,there is a significant difference in the elastic skeleton storativity between both sides of the ground fissures.