| Karst aquifer,as a more complicated aquifer system,is an aqueous medium containing various void structures such as pores,fissures,karst pipes,small karst caves,etc.The difference in regional karst development degree makes the void structure highly anisotropic and heterogeneous as well as unevenly distributed,which seriously affects the groundwater movement state machine law in karst areas.Therefore,the study of the hydraulic properties of the void structure of aqueous media provides a scientific basis for better understanding of groundwater movement in karst areas.In this paper,Jinan Spring was taken as the research object,and the concentrated discharge area was the main research area.Based on the analysis of the regional geological and hydrogeological conditions in the study area,indoor physical experiments,simulation,CT scanning,3D reconstruction technology,layered monitoring of groundwater,tracer test,water level correlation analysis,porous medium seepage simulation and CFP dual medium coupling simulation methods were used to study the hydraulic properties of the void structure of aqueous media.The hydraulic properties of the fissure structure were mainly analyzed,and the location of single karst pipeline structure in the concentrated discharge area of the Jinan spring area was determined.The dual-media coupling model was used to simulate the spring level dynamics,and the influence of the hydraulic properties of the void structure on the spring was analyzed and studied.These works provide a scientific basis for more accurate warning of the dynamic changes of spring water levels and timely formulation of measures to protect karst springs.Through the above analysis and research,this paper mainly drawn the following conclusions:(1)Taking the limestones of Bei'anzhuang Formation and Sanshanzi Formation in Jinan Spring as an example,CT scanning and 3D reconstruction technology were used to quantitatively study the void structure of this experimental core,and indoor seepage experiment and simulation were conducted using sample cores.The resultsshowed that the laws of fissure flow and pore flow are not conform to Darcy's law Linearity.(2)The analysis of the indoor fracture flow experimental data combined with the typical nonlinear hydraulic property formula found that from the perspective of the squared error of the fitted data and the actual physical significance,the Darcy-Weissbach formula is more suitable for expressing the focus on the fracture structure The hydraulic properties of the core flow.At the same time,an improved Darcy-Weissbach formula was formed,which greatly improves the fitting accuracy of theoretical calculation flow and experimental data.(3)A tracer test was carried out according to the hydrogeological profile of the study area and the groundwater flow field,the tracer concentration monitoring data of the monitoring points during the tracer test was recorded,and the number of karst pipelines in the study area can be determined according to the number of peaks in the tracer concentration curve at the spring position.The application of this method in the discharge area of Jinan spring area showed that there is a single karst pipeline.(4)This paper established a regression equation of the observed water level data of the observed hole and the spring water level within the tracer test range,and obtained the correlation coefficient according to the regression equation.In addition,combined with layered monitoring of groundwater quality and the location of karst development in the borehole data,the horizontal extension and vertical distribution of the karst pipeline are determined.The application of this method in the discharge area of Jinan spring area showed that there is a karst conduit at the elevation of 15.93 m in S1 Well — the elevation of-25.71 m in S4 Well — the elevation of-37.34 m in S10 Well — the elevation of-39.84 m in Baotu Spring.(5)In this paper,a numerical model of groundwater flow in the Jinan spring area was established,and the identification and verification stages of porous medium seepage simulation were completed.The fitting result of the water level have reached the accuracy requirements,and the sum of squared error between the calculated value and the measured value of the Baotu Spring water level is 6.632.Based on the simulation of porous media seepage,the MODFLOW-CFP program was used toconduct the seepage-pipe flow coupling simulation,and the sum of squared error between the calculated value and the measured value of the Baotu Spring water level is 3.065.The dual-medium coupling model can more accurately simulate the dynamic changes of Jinan spring water level.(6)The article analyzed the influence of the tortuosity,diameter and roughness of the fissure structure on the flow rate or spring water level.The study found that there is a linear proportional relationship between the increase of the simulation value of spring water level and the increase of pipe tortuosity.The relationship between the rising amplitude of the spring water level simulation value and the increasing diameter is a power function.In the turbulent state,the flow in the pipeline decreases with the increase of roughness,and the decrease trend follows the law of logarithmic function. |
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