| Land subsidence occurs frequently and widely all over the world,which will cause uneven settlement of urban buildings,road traffic and pipeline system lines and thus be destroyed;Will also give drainage,flood control,urban waterlogging prevention and control bring many difficulties。According to statistics,since the founding of the People’s Republic of China to the beginning of the 21st century,the loss caused by land subsidence is as high as 450-500 billion yuan,with an average annual loss of 9-10billion yuan,which seriously affects the economic and social development of Our country.Therefore,it is very necessary to conduct the spatial and temporal distribution characteristics of groundwater level and land subsidence.The two-step model cannot reflect the land subsidence problem under the action of soil and water coupling,and the fully coupled model is difficult to model,complicated calculation parameters,long calculation time,and difficult to stabilize the model,which is not suitable for the calculation of large area settlement model.The partially coupled model can simulate the deformation of various water-bearing media and the parameters involved in the model are simple and the calculation is clear.In this study,GMS-SUB module was used to establish a partial coupling model of groundwater seepage and land subsidence to simulate the dynamic changes of groundwater level and land subsidence in the study area of Taigu East Station,providing a reliable means for the quantitative study of land subsidence.(1)In this paper,the soil mass in the study area is quantitatively analyzed based on borehole data.The basic physical and mechanical indexes of soil samples were analyzed by geotechnical test,and the curve of consolidation process was obtained by consolidation compression test,and the law of compression deformation of soil was studied.The correlation between compressibility index and physical and mechanical index of soil is analyzed and the law is found.The natural density and particle density of soil samples increase first and then decrease with the increase of depth,while the natural water content increases first and then decreases with the increase of depth,which has a great correlation with the density.The size of the pore ratio also approximately reflects the size of soil moisture content,and the pore ratio of soil sample is positively correlated with the water content of soil sample.The overall change of soil sample saturation tends to be stable with sampling depth,and the natural water content is positively correlated with the liquid index,which means that the state of soil is relatively fluid with the increase of natural water content.The compressibility of soil decreases rapidly at first,then decreases obviously,and finally flattens out.The buried depth of soil has great influence on the compression and consolidation of clay soil,and the compressibility of clay soil generally decreases with the increase of soil depth.The regression equation of soil compression coefficient and compression modulus with liquid limit,water content,porosity ratio and natural density was obtained by correlation analysis.The parameters of inelastic water release rate and elastic water release rate,as well as the equivalent thickness and equivalent factor parameters of lagging water release interlayer are calculated from soil index.(2)Based on the data of physical geography,regional geology and hydrogeological characteristics of the evaluation area of Taigu East Station,the hydrogeological conceptual model and mathematical model are established to simulate and predict the groundwater level and land subsidence in the evaluation area.The average decline rate of the overall water level in the evaluation area is 1.11 m/a.In August 2016,the water level in the partial area of the second confined aquifer reached the roof of the aquifer,and the middle and deep water falling funnel was initially formed.The center of the falling funnel was located in Sangzi Village,1 km to the east of Taigu East Station,and the buried depth of the water level in the center of the funnel was 48.7 m.In the prediction period of Taigu East Station,the accumulative land subsidence was up to51.2mm.The area of the settlement funnel can reach 10.64 km~2.(3)The temporal and spatial response characteristics of groundwater level and land subsidence in the evaluation area are studied by using the time series analysis method in statistics to study the law between each amount of water level decline and land subsidence in the evaluation area.From the analysis results of time series of water level,the autocorrelation coefficient R_k decreases with the increase of lag time K,indicating that the autocorrelation of time series of water level at each point gradually weakens.When the lag time K increases to a certain extent,the autocorrelation coefficient R_kappears negative,indicating that the fluctuation of groundwater level contains periodic components.At each point,the autocorrelation coefficient R_k decreases from 1 to 0 after a lag of about 58 days,indicating that the water level on the 58th day has no correlation with the previous one.According to the analysis results of subsidence time series,the subsidence autocorrelation coefficient R_k continues to decrease steadily within 0-20days after the initial subsidence,which proves that the decline of water level of clay interlayer has a lag and there is a lag phenomenon in the compression of clay interlayer.Attention should be paid to the water level near Taigu East Station and the expansion of the landing funnel.The prediction of water flow field can provide reference for the planning,configuration,management and protection of groundwater in Taigu East Station area,and can reduce the pumping of groundwater in Taigu East Station area or rationally arrange the mining scope of pumping wells.At the same time,the prediction of settlement provides reference for the prevention and control of the settlement and planning of Taigu East Station area,do the corresponding prevention and control measures,reasonably raise and stabilize the foundation in the railway lot with large settlement,avoid the damage to the ground buildings and endanger the property and life due to the ground settlement.Figure[61]Table[19]Reference[94]... |
