Numerical Simulation Of Groundwater In Consolidation And Drainage Of Clay Soil Layers On Top And At Bottom Of The Confined Aquifer

Land subsidence is one of the environmental geological problems caused by over-exploitation of groundwater,which inevitably increases the effective stress experienced by the top and bottom of the confined aquifer.It results in the compaction and consolidation of clay soil.The released weakly bound water participates in the seepage and supplies the adjacent confined aquifer,becoming a source of supply for confined aquifers under mining conditions.And it is also accompanied by changes in the permeability of the clay layer.These factors directly affect the reliability of numerical simulation results.Therefore,it is necessary to quantify the variation range of the pressure-reduced water release and the permeability coefficient caused by consolidation drainage,and carry out the groundwater numerical simulation study under the of the consolidation drainage conditions,to improve the precision of the groundwater numerical simulation model and protect groundwater mining environment.For this reason,this paper focuses on the relevant contents of groundwater numerical simulation under consolidation drainage condition of top and bottom floor in Fuyang city,Anhui province.Firstly,based on the detailed analysis of geological hydrogeological conditions,groundwater exploitation status and land subsidence evolution in the study area,this paper expounds the formation mechanism of ground subsidence caused by groundwater over-exploitation and clarifies the compression horizon.The analysis results show that the main horizon of the ground deformation is in the depth range of 84.5 to 200 m.The amount of land subsidence shows an increase with the increase of confined aquifer production.Affected by the consolidation and creep of soil in the aquitard and aquifer floor of the aquifer,the change of groundwater level in the first confined aquifer slightly lags behind the rate of land subsidence change,and shows a significant negative correlation.Based on the above results,a series of consolidated drainage tests were carried out on the confined aquifer roof undisturbed core soil samples under different pressure conditions in order to further reveal the relationship between the compression and drainage volume of saturated clay soil,the relationship between the coefficient of expansion of soil consolidation and external force,and the law of permeability of soil in consolidation process.The experimental results reveal that when the external force is greater than the shear strength of the weakly bound water in the soil,some of the weakly bound water participates in the pore seepage and turns into free water,that is the volume expansion effect.The expansion coefficient is a power function relationship with the external force,and the soil permeability coefficient K decreases exponentially with the increase of the external force.However,the stability of the soil seepage has a time lag due to the discharge of weak combined water.Using Visual MODFLOW software,a numerical model of groundwater under the conditions of top-bottom soil consolidation was established by taking account of the changes of parameters such as soil displacement,consolidation drainage expansion coefficient,and permeability coefficient of soil in settlement process(space and time).Combined with the soil deformation equation,the partial phase coupling equations were used to simulate the change process of groundwater flow field and land subsidence in space and time.During the simulation period,the consolidated drainage of soil in the study area accounted for 6.11% to 8.85% of the total exploitation volume of the confined aquifer.Secondly,due to the consideration of the change of the permeability coefficient of the soil in the top and bottom of the confined aquifer and the consolidation of the soil to the groundwater flow,the accuracy of the calculated and measured values of the water level of the observation well and the calculated and measured value of the accumulated land subsidence of the observation are improved.With the aid of this numerical model,a groundwater level and exploitation dual-control scheme was proposed based on land subsidence constraints.When the constrained water production volume is increased by 25%,the water level rises significantly,and the cumulative land subsidence at the center point is basically stable at 1846 mm.After 2020,the land subsidence basically becomes stable and does not increase.