Simulation Study On The Settlement Of Collapsible Loess Foundation Caused By The Rise Of Groundwater Level

At present,there are few studies on calculation models and calculation methods of settlement deformation of collapsible loess foundation caused by lake water leakage,and there is insufficient experience for reference.However,once the subsidence deformation of the collapsible loess foundation is too large,the building cannot be used normally when the impact is small,and it will bring great harm to people's life,property and personal safety when the impact is heavy.Therefore,the safety and stability of collapsible loess foundation cannot be ignored.When the groundwater level rises,the water content of the foundation soil increases,and the coupling effect of increased water pressure and pressure leads to catastrophic settlement accidents.Humidification deformation is the additional deformation due to the increase in water content after the deformation reaches stability under pressure.The key to humidification deformation is to study changes in water content.In this paper,FLAC3 D simulation study is conducted on the settlement deformation of loess foundation due to lake water leakage.However,the increase in water content softens the original loess structure,water dissolves part of the colloid and salt base,and the loss of suction connection produces collapsing deformation,which is a microscopic change.This change in microstructure is generally difficult to simulate with finite element software.The FLAC3 D software does not set up a constitutive model for loess collapsing.In response to this problem,this paper analyzes the theory of unsaturated seepage to obtain the soil-water characteristic curve of unsaturated soil,and studies the water infiltration law in loess.Then use Geo Studio software to study the moisture distribution of the foundation soil caused by lake water leakage.Combined with the relevant knowledge of damage mechanics theory,the linear relationship between the natural logarithm of the compression modulus and the water content is obtained,and the compression modulus after damage is equivalently substituted for the compression modulus.In this way,FLAC3 D can simulate the settlement of collapsible loess foundation.And came to the following conclusion:(1)After the rebuilding of the Qujiang Nanhu Lake,the groundwater level in the area gradually increased in the event of lake water leakage.With the increase of the distance from the lake,the elevation of the groundwater level shows a trend of "less-more-less".In the foundation soil 210 meters away from Qujiang South Lake,the groundwater level showed a slow-fast-slow rising trend.Eventually the groundwater level rises about 1.5 meters.(2)The change of water content in foundation soil with time mainly shows two types.One is that with the increase of time,the water content shows a rapid increase first,then slowly increases until saturation;The other is that the water content increases rapidly with time,then slowly increases,and finally decreases slightly due to gravity.(3)The relationship between and is obtained.With the increase of water content,the tangent compression modulus gradually decreases,and the natural logarithm of the tangent compression modulus has a linear relationship with the water content.The calculation formula of and is obtained.(4)FLAC3D simulation results show that after two years of lake water leakage,the groundwater level of the surrounding soil will change due to the rise of the surrounding groundwater level,and the building will have an additional collapse deformation of about 12.5 cm.When only the saturated collapsible deformation of the soil layer below the groundwater level is considered,the additional settlement generated by the building is about 6.4 cm.