Study On Influence Factors,Prediction And Evaluation Of Land Subsidence In Cangzhou

With the rapid development of economy and society in Cangzhou area,deep groundwater,geothermal,oil,natural gas and other underground resources continue to be developed,especially the deep groundwater overdraft,long over-exploitation,formed a deep groundwater depression funnels covering the region,and then gradually induced a land subsidence.With the passage of time,land subsidence developed rapidly,and covered the entire Cangzhou area,with the amount of subsidence large,the rate fast,and wide range of subsidence,it has become one of the more serious subsidence area ground in North China Plain and even in the country,has become a major environmental and geological issues affecting the sustainable development of regional economy and society.In this paper,take the Cangzhou area as the object of study,collect the relevant geological data of the study area,comprehensively analyze the geological background,drilling data,monitoring information and data,groundwater exploitation and land subsidence development in the Cangzhou area,the factors that lead to the settlement of the ground in Cangzhou area and its related laws are studied,and forecast according to the development trend of land subsidence under different mining conditions.Based on the forecasting results,the development trend of land subsidence in Cangzhou area is evaluated.The main research results are as follows:Based on the method of ARCGIS software spatial analysis and InSAR monitoring technology,the development process and current situation of land subsidence in Cangzhou area are summarized from the aspects of cumulative settlement distribution and settlement velocity distribution of land subsidence.The land subsidence began in the 1970 s,with the groundwater exploitation intensity continues to increase,the phenomenon of land subsidence is becoming more and more serious from the Cangzhou settlement center developed into Renqiu,Suning,Cangzhou City,Qingxian and other multi-center complex.The settlement of Cangzhou City subsidence center is 2600 m.With the limitation of groundwater exploitation in Cangzhou city in recent years,the settlement of Cangzhou settlement center is alleviated and the annual settlement rate is reduced to 10.84mm/a,but deep groundwater production of the surrounding counties and cities increased,the overall settlement of the region has a rebound trend.The whole settlement area shows that the development of the city is more serious than that of the suburbs.The urban residential area is more serious than the agricultural planting area,and the western part is more serious than the eastern region and the economically developed areas are more serious than the underdeveloped areas.The main reason is that urban development requires the exploitation of large amounts of groundwater,especially in economically developed cities on the groundwater demand even more,and the exploitation of groundwater has an important effect on the development of land subsidence.According to the InSAR monitoring chart in recent years,2014 compared with 2013: the overall trend to accelerate,mainly reflected that the city land subsidence rate increased 10-20 mm /a.2015 compared with 2014,the overall tends to be gentle,the main reason is that the rainfall imbalance led to a large amount of groundwater in 2014,the amount of mining in 2015 is small,which reflects the groundwater exploitation is closely linked to land subsidence.By overlaying the annual ground rates,the new trend of land subsidence in recent years is shown,and the land subsidence is divided into four different subsidence zones according to the land subsidence rate.The mechanism of land subsidence in Cangzhou area is expounded by means of the effective stress theory of Terzaghi.At the same time,the factors affecting land subsidence are analyzed,to determine that the land subsidence in the study area is essentially hydrothermal and engineering geology phenomenon.The intrinsic factor is that there is a cohesive soil layer in the formation that can be compressed,external factors for the exploitation of a large number of groundwater.In order to study the factors that cause the land subsidence,First of all,from the external factors that cause land subsidence,With the spatial analysis capabilities of Arcgis software,based on the geological and environmental conditions of Cangzhou area,based on the analysis of the correlation between groundwater exploitation and land subsidence,the relationship between groundwater exploiting and land subsidence,the correlation between groundwater level and land subsidence rate,a comprehensive and systematic study on the law of land subsidence affecting groundwater exploitation in Cangzhou area is carried out.The results show that the land subsidence in Cangzhou area is closely related to groundwater exploitation,the groundwater extraction stage corresponds to the development phase of the land subsidence,The land subsidence and the groundwater funnel are consistent with the development trend of the spatial distribution position,and the land subsidence accounts for about half of the groundwater exploitation,and with the increase of mining time,the proportion gradually decreased,The land subsidence rate is positively correlated with the groundwater level,which changes with the change of groundwater level,and some strata are lagging behind.Lag period is about a month,From the long-term changes,there is a linear regression relationship between the groundwater level and the cumulative land subsidence,And according to the regression curve in the Cangzhou area of groundwater level there is 40 m warning water level down value,beyond this value,as the water level is increasing,the accumulated settlement will increase.70 meters is the limit water drawdown value,Beyond the water level,the land subsidence will show a straight up trend.Then,based on the analysis of existing monitoring data and drilling data,combined with the actual geological conditions and geological structure,the compression layer group of land subsidence in Cangzhou area is divided into three compression layers from the internal factors that cause the land subsidence,and the overlay analysis of the land subsidence area and the compression layer thickness map is carried out,It can be seen that there is a correspondence between the subsidence area and the compressible layer,and the serious area of sedimentation is often a region with a thicker compression layer.Through the hierarchical scale land subsidence monitoring data processing.This paper analyzes the existing land subsidence model,and selects the groundwater-land subsidence coupling model as the land subsidence prediction model in Cangzhou area for the actual situation in Cangzhou area.Through the research above,on the basis of deep analysis of hydrogeology and engineering geological conditions in the study area,a series of conditional factors such as the state of groundwater flow,the structure of aquifer,the boundary condition and the nature of parameters are comprehensively generalized,sources and sinks in the study area were calculated.The conceptual model of hydrogeology and the mathematical model of groundwater flow are established,and the GMS software is used to simulate the groundwater flow field from December 2014 to December 2015 in Cangzhou area.Based on the one-dimensional consolidation theory of Terzaghi,mathematical generalize the soil deformation theory,specific to the delayed release effect of the cohesive soil layer,The viscous soil layer is divided into a lagging clay layer and a nonhysteresis clay layer,and Mathematical generalize the water release mechanism respectively establish the land subsidence mathematical model,then construct the land subsidence model The groundwater numerical model is coupled with the land subsidence model to obtain the groundwater flow-land subsidence coupling model,And the submodule in GMS software was used to simulate the land subsidence process in Cangzhou area and the model parameters are corrected by 2015 settlement data.So that the model can simulate the development of land subsidence correctly.Firstly,based on the present situation of groundwater exploitation in 2015,this chapter predicts the development trend of land subsidence in Cangzhou area.Through the forecast results can be seen,by 2020,Cangzhou groundwater main mining layer has a larger level of water drop,the development of this stage of serious areas are Renqiu City,Suning County,Xianxian County,Cangxian County,Qingxian County,Nanpi County,Dongguang County.The maximum ground subsidence of each area is 231 mm,214.5mm,163 mm,216mm,246.8mm,241.6mm respectively.Then,based on the annual assessment index of groundwater intake in Cangzhou City(2016 ~ 2020),the development trend of ground subsidence in Cangzhou area is forecasted according to the reduced exploiting amount from 2016 to 2020,It can be seen from the forecast results that the groundwater level will decrease gradually with the passage of time.By 2020,the groundwater level will recover and increase by 5m,and the settlement will be controlled.The maximum settlement is 143.2mm,which is far less than the amount of ground subsidence under the subsurface exploitation.It shows that the effect of the exploiting reduction program is obvious,so that the development of ground subsidence has been controlled.Finally,take Cangzhou as the research area,based on the forecast results of 2020,analyze and study the natural attributes of the land subsidence disaster in Cangzhou area,evaluate the risk of land subsidence by geographic information system(ARCGIS)and fuzzy hierarchy evaluation method.Draw land subsidence risk zoning map(the first map),based on the socio-economic,population and urban development of the subsidence area,combined with the geographic information system(ARCGIS),study the social properties of the land subsidence disaster quantitatively,evaluate the vulnerability of the disasterbearing body and plot the land subsidence vulnerability map(the second map).Through the spatial analysis technology of ARCGIS software,superimpose and combine the land subsidence risk zoning map and land subsidence vulnerability zoning map,draw the land subsidence hazardness evaluation partition map(the third map),use the " Three Maps Method " evaluation method,Completed the hazardness evaluation of land subsidence in Cangzhou area.Provide a scientific basis for the plan of development of the future Cangzhou.