Study On The Law Of Soil Deformation And Land Subsidence In The Typical Area Of Beijing Tianjin And Hebei

Since sustainability of groundwater over-exploitation,Hebei Plain underground water level continued to decline,and a series of slowly changing geological disasters such as land subsidence and ground fissures will follow.Langfang is located between Beijing and Tianjin,with a superior geographical location.It belongs to the confluence area of Hebei Plain and Beijing Plain.In response to the country's requirements for the comprehensive prevention and control of land subsidence,the paper relies on the project of China Geological Environmental Monitoring Institute(DD20160235)"Investigation of Ground Subsidence and Ground Fissures in Beijing-Tianjin-Hebei Area and Monitoring of the Geological Environment"to determine the physical and mechanical properties of the soil and the law of land subsidence.By geotechnical tests and high-pressure consolidation tests to determine the physical and mechanical indexes of each soil layer,analyze the correlation between the indexes and compressibility indexes,and the influence of particle size and the depth on the compression deformation of the soil layer.Based on the results and survey data,a three-dimensional finite element model of the Langfang planning area was constructed,and the land subsidence problems were analyzed and predicted.The following main conclusions were obtained:(1)Analyzed the parameters of soil within 0?405m,studied the law of different physical indexes with depth,and obtained the relationship among compressibility,compressibility modulus,depth,void ratio,natural density,liquidity index,sand grain and moisture content which can be expressed by a linear regression equation.The compressibility decreases with the increase of the consolidation pressure,showing a good negative linear relationship in the double logarithmic coordinate system.The specific gravity and plasticity index of soil samples at different depths have a linear positive correlation,and the void ratio has a linear relationship with water content and natural density.(2)Through high-pressure consolidation and ultra-high-pressure consolidation tests,the consolidation process change curves of shallow and deep clay soils are obtained.The results show that the curve changes in the main consolidation stage of deep soil and shallow soil are similar,but the consolidation pressure required for deep soils to reach the inflection point(the yield point)is greater,and the pressure required to complete the consolidation is greater.Clays of different particle size distribution of the consolidation process has been studied,and knew that the smaller the unevenness coefficient(22.8>C_u>5),the greater the deformation under the same consolidation pressure,and the greater the curvature coefficient(1.3>C_c>0.2),the greater the deformation under the same consolidation pressure.(3)Combining the results of test and field surveys,the model of the Langfang planning area were established to predict the cumulative land subsidence of the planning area in 2030.After 10 years of mining with the current mining trend,the settlement center located in the city center will continue to sink,but the rate will be significantly reduced;considering the changes in the planting structure in the west,the demand for water levels in the first and second aquifers will decrease,which may occur in 2030 The ground rises,estimated to rise by 50-60mm,with a maximum of 80mm.