【作者】 张力；

【导师】 何继善；

【作者基本信息】 中南大学 ， 地球探测与信息技术， 2011， 博士

【摘要】 坑道直流电阻率法勘探技术以其简便、经济和资料易于解释的优点被广泛的应用于坑道超前预报工作中。但是由于自身工作方式以及工作环境的限制,测量时掘讲堂子面后方坑道腔体及坑道表面不均匀干扰始终是传统坑道直流超前探测无法避免的影响因素。针对此问题,阮百尧提出了利用同性点源的相斥、聚集原理进行坑道勘探的新技术-直流聚焦电阻率超前探测技术。本文在国家自然科学基金项目(40774057)的资助下,进行了基于电流聚焦理念的坑道掌于面和坑道底板及侧壁的垂向聚焦超前探测方案研究。作为坑道直流超前探测中一种全新的方法技术,有必要选取适用的技术手段对其工作机理和应用条件以及探测能力进行分析评价。应用有限元数值模拟技术对二维轴对称分布和三维全空间分布的坑道环境下直流聚焦超前探测方案的可行性及效果进行数值模拟研究。分别采用8节点四边形双二次单元和20节点六面体双二次单元对二维和三维研究区域进行剖分。对二维区域电位及电导率分布进行线性插值。三维空间电位采用双二次插值,电导率采用三线性插值,进行异常电位的求解。以此提高坑道局部环境下数值模拟的稳定和精确性。采用行索引一维压缩存储格式,节省了大量的计算机内存,配合存储格式应用高效的分裂型预条件共轭梯度算法求解大型稀疏线性方程组,使三维数值模拟单点计算可以即时完成。在数值建模时考虑到坑道腔体的存在,直接将其所在单元节点信息引入到整体方程组的求解过程中。相同条件下数值计算结果与解析解和土槽物理实验结果吻合,满足数值模拟需要。用两章篇幅结合模型计算分别对掌子面垂向聚焦装置和坑道侧壁垂向聚焦剖面装置的场源分布特征、探测效果、适用性以及抗干扰能力进行了详细的讨论和分析。应用多个组合模型分别对比计算了掌子面三极聚焦装置、五极聚焦装置和九极聚焦装置对掘进前方聚焦场中异常体的响应,最后从勘探效果和实用性的角度选取掌子面五极聚焦装置为最佳方案。相对掌子面装置坑道剖面垂向聚焦方案电极排列方式要丰富许多。文中提及的剖面测量装置有聚焦双极装置、聚焦三极装置和聚焦五极装置,均可以进行电位和电位梯度测量。而且双极聚焦装置根据勘探目的的不同还可以通过改变电极排列万式延伸出中心测量方式、单边测量方式和双边测量方式。经过典型模型的计算,达到了预期的设计效果,说明上述垂向聚焦剖面装置设计方案正确可行。通过屏流比的概念将屏蔽电极和主探测电极中发射的电流联系到了一起,模型计算说明改变屏流比参数,可以改变聚焦场中屏蔽电流对主探测电流的约束作用。常规坑道直流探测方案经过多年发展和实践的检验已经被证明是可行的。文中通过类比坑道常规直流装置电极排列方式,应用同性源聚焦装置进行坑道剖面及剖面测深计算,结果显示能够达到相应坑道直流常规装置的勘探效能。但是也存在问题,采用异性点源装置等效得到的同性垂向聚焦装置视电阻率转换公式进行计算后得到的视电阻率参数出现负值,分析认为这与源场的分布特征及异常响应机理相关。建议今后在这方面进行深入研究。源场的分布特征直接关系到异常资料的解释和评判,文中针对各种模型设置及装置类型应用MATLAB二维有限元数值模拟工具对相应的异常场中电位及电流密度分布以图形方式进行了直观表示。更多还原

【Abstract】 Tunnel DC resistivity methods are widely used in tunnel advanced exploration with the advantages of being simple, cheaper and easy to interpretation, compared with others. However, due to the restriction of the survey configuration and working environment, it is impossible to avoid the interferences of tunnel cavity and the heterogeneous accumulations behind the tunnel face, for the conventional tunnel direct-current advanced prospecting. To solve this problem, Bai-Yao Ruan proposed a new exploration technique for tunnel advanced detection, i.e., DC focusing resistivity advanced detection method. It is based on the principles of repulsion and focusing like point sources. Supported by the National Natural Science Foundation of China (Project Number:40774057), this thesis focuses on the advanced detection measurements with vertical focusing arrangement on the tunnel face and tunnel wall, based on the idea of electric current focusing effect. As a new method of direct current advanced detection in tunnel, it is necessary for us to develop appropriate techniques to analyze and appraise the working principle, application conditions and exploration capability of the measurements.In this thesis, a numerical simulation method of finite element was used to evaluate the feasibility and effect of focus DC current advanced detection in tunnel for several models with2D axial-symmetric structure and3D full space structure. At first, the2D and3D target model is divided into finite rectangular elements and finite hexahedron elements with bilinear variation in conductivity respectively. Then linear interpolation was used to achieve the potential within each element for2D model. For3D model, we use bilinear interpolation for the conductivity and3-D linear interpolation for the potential as to get the anomalous potential, whereas it should improve the stability and accuracy in the numerical simulation. To save the computer memory, an iterative solver based on the splitting pre-conjugate gradient and row compressed storage scheme were employed to solve the linear system with less computation time. During the numerical modeling, the existence of cavities was considered, its information was directly included into the linear system during the process of solving the equation. Under the same conditions, the results gained with FEM are consistent with the result gained by the physic experiment.In the first two chapters, we give a detailed discussion and analysis of the field source distribution, exploration ability, applicability and anti-noise capability of tunnel face vertical focusing device and tunnel wall vertical focusing profile device. The response of anomalous body for three-electrode focus current array, five-electrode focus current array and night-electrode focus current array applied to tunnel face were modeled by multiple combination models. Finally, five-point focus current array is proved to be optimal in terms of exploration effects and practicability. Generally, tunnel wall focus current profile arrays are plentiful compared to tunnel face focus arrays.The measurement configuration mentioned in this paper, e.g., two-pole focus array, three-electrode focus array and five-electrode focus array, can be applied to potential and potential gradient measurement. Moreover, the bipole focus array can be extending to different survey configurations, e.g., center measurement method, unilateral measurement method and bilateral measurement method, according to different exploration purpose. The numerical results for several typical models, show that the vertical focus profile array design is effective and practical.Based on the concept of’PLB’, we build the relationship of the current from the shielding electrodes and from the primary electrode. The model calculations show that we can control the restriction of shielding current on primary current in focusing field, by the parameter’PLB’After years’development and experiment in practice, conventional tunnel DC detection method has been proved to be effective. In this paper, focus current array, for the tunnel conventional DC electrodes arrangement device, was applied to profile prospecting and sounding in tunnel, and the numerical results show that the focus current array could achieve the corresponding exploration efficiency compared to conventional DC device. However, there are also some problems, e.g., the apparent resistivity appears negative, calculated form the resistivity calculation formulas for the homogeneous point-source device. This may result from the source distribution characteristics and anomaly response mechanism.Source distribution characteristics directly affect the interpretation of field data and the judgment of anomalous bodies.2D finite element numerical simulation tools based on MATLAB were used to modeling the distribution of abnormal potential and current density for different models and array types.更多还原