Study on the Hydraulic Characteristics of the Void Structure of Karst Aquifer in Jinan Spring Area

董亚楠

邢立亭;李常锁

硕士

济南大学

空隙结构;;CT扫描与三维重建;;渗流实验与模拟;;水力性质;;耦合模拟

岩溶含水介质是一种包含了孔隙、裂隙、岩溶管道、小溶洞等多种空隙结构的复杂含水层体系,区域岩溶发育程度的不同使得含水介质的空隙结构具有高度的各向异性和非均质性以及分布不均一性,严重影响了岩溶地区地下水的运动状态与规律,因此,研究含水介质空隙结构的水力性质对更好地掌握岩溶地区地下水运动提供一定的科学依据。本文以济南泉域为研究对象,集中排泄区为主要研究区域,对研究区的区域地质、水文地质条件进行分析的基础上,采用室内物理实验、仿真模拟、CT扫描和三维重建技术、地下水动态分层监测、示踪试验、水位相关性分析以及多孔介质渗流模拟和CFP双重介质耦合模拟等方法,对济南泉域含水介质空隙结构的水力性质进行了一定的研究,主要分析了裂隙结构的水力性质,确定了济南泉域集中排泄区的单一岩溶管道结构的位置,进行了双重介质耦合模型对泉水位动态的模拟,并分析研究了空隙结构水力性质对泉水的影响,为更精准地预警泉水位动态变化,及时制定保护岩溶大泉措施提供科学依据。本文通过上述分析研究,主要得出以下结论:(1)以济南泉域内的北庵庄组和三山子组灰岩为例,采用CT扫描以及三维重建技术定量地研究了本次实验岩心的空隙结构,并对试样岩心进行室内渗流实验和仿真模拟,结果表明裂隙流和孔隙流运动规律都不符合达西定律的线性规律。(2)分析了室内裂隙流实验数据与典型非线性水力性质公式之间的关系,结果发现,从误差分析角度以及实际的物理意义角度,达西-韦斯巴赫公式都比较适用于表达注重裂隙结构对岩心水流运动作用时的水力性质。同时,形成了改进后的达西-韦斯巴赫公式,使理论计算流量与实验数据的拟合精度大大提高。(3)根据研究区域的水文地质概况以及地下水流场进行了示踪试验,记录示踪试验过程中监测点的示踪剂浓度监测数据,观察位于泉位置的示踪剂浓度变化曲线图中的波峰数量可以确定研究区域中的岩溶管道数量。该方法在济南泉群排泄区应用验证表明济南泉群上游存在着单一岩溶管道。(4)将落入示踪试验范围内的观测孔水位观测数据与泉水位建立回归方程,根据回归方程求得相关性系数,并且对研究区域内的地下水监测孔进行地下水水质分层实时监测,以及结合钻孔资料中岩溶发育的位置进行综合考虑可以确定岩溶管道的平面延伸位置以及垂向分布位置。该方法在济南泉群排泄区应用验证表明,济南泉群上游S1孔标高15.93m处—S4孔标高-25.71m处—S10孔标高-37.34m处—趵突泉标高-39.84m处存在单一的岩溶管道。(5)建立济南泉域地下水水流数值模型,完成了多孔介质渗流模拟的识别与验证阶段,水位的拟合结果均达到了精度要求,且济南趵突泉的计算水位值与实测值之间的误差平方和为6.632。在多孔介质渗流模拟的基础上,通过MODFLOW-CFP程序进行了渗流—管道流的耦合模拟,其趵突泉的计算水位值与实测值误差平方和为3.065,双重介质耦合模型能够更加精准地模拟济南泉水位的动态变化过程。(6)对裂隙结构的曲折度、直径以及粗糙度对流量或泉水位的影响进行分析,研究发现泉水位模拟值的上升幅度与管道曲折度的增加幅度之间具有线性正比关系,泉水位模拟值上升幅度与直径的增加幅度成幂函数关系,管道内流量在紊流状态下随着粗糙度的增加而减小,且减小趋势服从对数函数规律。

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.