二维条件下洞室周围非饱和带变化的EVRT响应特征及成像研究

发布时间：2018-02-26 03:27

本文关键词： ERT EVRT 洞室非饱和带含水量参数求解水流入渗　出处：《南京大学》2013年硕士论文　论文类型：学位论文

【摘要】：在水文地质和工程地质领域,针对地下洞室周围非饱和带的研究目前是理论研究的重点和难点,针对洞室周围的地下水的运移研究目前也缺少直接而有效的实时监测手段。本研究通过室内建立物理模型,基于高密度电阻率成像技术ERT(High-density Electrical Resistivity Tomography)引入了高密度电阻相对变化率成像方法EVRT (High-density Electrical Resistance Relative Variation Rate Tomography)用于探求上述问题。EVRT基于ERT的数据采集手段,通过实验过程中介质相对于初始时刻背景电阻值的变化进行实时成图。由于多孔介质含水量的改变会引起电阻值的变化,因此EVRT图像的变化能实时反映出实验中多孔介质含水量的变化。EVRT方法是对洞室周围非饱和带研究及水流运移研究的创新和完善。本研究首先通过水中异常体实验验证了在二维洞室条件下EVRT的可行性和有效性,同时研究了NaCI溶液脉冲实验中NaCI溶液在水中的运移。在此基础上,在两种不同的洞室物理模型(半圆形洞室和拱形完整洞室)中设置各类多孔介质进行饱和排水实验,研究水流在不同多孔介质条件下的运移路径及非饱和带的形成与变化规律。最后利用GMS软件中的Seep2D模块进行了数值模拟并与EVRT图像进行了对比。通过上述研究获得了以下成果：(1) EVRT有效性验证方面EVRT能准确反映水中异常体的位置、大小等信息,证明了EVRT在二维洞室条件下的可行性和有效性。EVRT也可以有效的反映NaCI溶液在水中的运移路径。同时,本研究发现溶液脉冲实验后NaCI溶液静止时出现了明显的盐度分层现象。(2)水流入渗过程监测方面：不同介质条件下,EVRT方法均可以有效揭示介质的含水量变化并反映水流在介质中的渗流路径。同时,不同的多孔介质具有不同的水流运移特征,这和多孔介质的粒径大小有关。(3)参数求解方面：多孔介质含水量的变化可以通过电阻随时问的变化曲线(R-t曲线)清晰地反映,同时水流在介质中的运移速度可以通过R-t曲线中电阻变化的拐点时间的先后计算得出,从而通过达西定律可以反求出多孔介质的渗透系数。(4)非饱和带识别方面：洞室周围的非饱和带在排水初期即迅速形成,非饱和带并非沿着洞室轮廓均匀向外扩展,而是沿洞室边壁的排水孔向外呈放射状分布。同时,洞室周围非饱和带的延伸深度与洞室周围多孔介质的粒径有关。(5)数值模拟方面：Seep2D模块可以有效模拟稳定流条件下洞室模型的流场和水头分布,与EVRT图像对比的结果表明,两种方法均能很好的反映出实验过程中不同介质条件下的流场分布。
[Abstract]:In the field of hydrogeology and engineering geology, the study of unsaturated zones around underground caverns is the focus and difficulty of theoretical research. There is also a lack of direct and effective real-time monitoring methods to study the movement of groundwater around the cavern. Based on the high density resistivity imaging technology ERT(High-density Electrical Resistivity tomography, a high density Electrical Resistance Relative Variation Rate tomography method, EVRT high density Electrical Relative Variation Rate tomography, is introduced to find out the above problems. EVRT is a data acquisition method based on ERT. In the process of experiment, the change of the resistance value of the medium relative to the background resistance value at the initial time is mapped in real time. Because the change of the water content of the porous medium will cause the change of the resistance value, Therefore, the change of EVRT images can reflect the change of water content in porous media in real time. The EVRT method is an innovation and perfection in the study of unsaturated zone around the cavern and the study of water flow migration. Firstly, the experiment of anomalous bodies in water is carried out in this study. The feasibility and effectiveness of EVRT under the condition of two-dimensional cavern are verified. At the same time, the migration of NaCI solution in water was studied in the pulse experiment of NaCI solution. On this basis, various porous media were set up in two different physical models of cavern (semi-circular cavity and arched cavity) to carry out saturated drainage experiment. This paper studies the migration path of water flow in different porous media and the formation and variation of unsaturated zone. Finally, the numerical simulation is carried out by using the Seep2D module in GMS software and compared with the EVRT image. The following results are obtained: 1) EVRT can accurately reflect the position of anomalous bodies in water in terms of EVRT validation. It is proved that the feasibility and validity of EVRT under the condition of two-dimensional cavern. EVRT can also effectively reflect the migration path of NaCI solution in water. In this study, it is found that there is obvious salt stratification phenomenon in NaCI solution at rest after the pulse experiment.) the monitoring of water infiltration process: under different medium conditions, the EVRT method can effectively reveal the change of water content in the medium and reflect the change of water content in the medium. The flow path in the medium. At the same time, Different porous media have different characteristics of water flow migration, which is related to the particle size of porous media. The solution of parameters is: the change of water content in porous media can be clearly reflected by the curve of change of resistance at any time (R-t curve). At the same time, the velocity of water flow in the medium can be calculated by calculating the inflexion time of the resistance change in the R-t curve. Thus, through Darcy's law, the permeability coefficient of porous media can be obtained in reverse. 4) the unsaturated zone around the cavern is formed rapidly in the early stage of drainage, and the unsaturated zone does not extend uniformly outward along the outline of the cavern. It is radially distributed along the drainage holes in the side wall of the cave. At the same time, The extension depth of unsaturated zone around the cavern is related to the diameter of porous media around the cavern. (5) numerical simulation of the flow field and water head distribution of the cavity model under steady flow conditions by using the: 1 / Seep2D module can effectively simulate the flow field and water head distribution in the cavity model under steady flow conditions. The results of comparison with EVRT images show that, Both methods can well reflect the flow field distribution in different media.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：P641.2;TU91;P631.322

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