【作者】 梁志刚；

【导师】 陈云敏； 冯卫；

【作者基本信息】 浙江大学 ， 岩土工程， 2005， 博士

【摘要】 本文结合国家自然科学基金项目“复杂环境作用下土坡的灾变机理及TDR监测”（50278087）,以影响边坡稳定最重要的物理参数之一土体的含水量变化监测、边坡是否产生滑动——滑动趋势监测以及边坡产生滑动时滑动面位置监测作为技术背景,系统地研究了土的电磁特性基本理论、同轴电缆传输系统在受拉伸和剪切时的反射特性、室内试验和现场工程应用。 首先,从极化机理出发,考虑土中电子或等离子体在电场中的动力特性,建立了电磁波与单相介质、混合介质相互作用的分析模型,给出了土颗粒、水、空气等单相介质介电常数ε_r的表达式 （ε_r-1）/（ε_r+2）=（1/3ε₀）（Ne²/（mω²+k））+（（ε_∞-1）/（ε_∞+2））和土体（混合介质）的介电常数表达式。将该表达式与现有的理论和经验公式进行了比较,发现本文表达式具有更明确的物理意义并适用于处于各种状态的各类土。 接着研究了测定土的介电常数的方法——同轴电缆电磁波反射技术。详细介绍了探头几何尺寸对介电常数量测结果的影响。在此基础上,为了研究不同类型探头对介电常数量测结果的影响,研制了三针式和六针式小型探头进行对比试验,研究表明,六针式探头比三针式探头的测试结果更为稳定可靠。在实际工程中,如土的孔隙比不太大,探头不会对土体有太大的扰动,宜选用多针式或圆筒形探头进行测试。 基于时域有限差分法推导了适合同轴电缆电磁波反射系统的计算式,并对同轴电缆传输系统和用于介电常数测试的同轴电缆电磁波反射系统进行了时域有限差分模拟,并与实测曲线进行了对比,发现对于同轴电缆传输系统,该方法能比较准确地模拟出其反射曲线。对用于介电常数测试的同轴电缆电磁波反射系统,当探头位于单层介质时,该方法能比较准确地模拟出其反射曲线;当系统位更多还原

【Abstract】 The water content measurement and landslide monitoring are both significant important for the research on mechanism of landslides under complicated situations. In this thesis, the electromagnetic properties of soil, reflecting properties of electromagnetic wave passing through stretched or sheared coaxial cable were studied theoretically and practically.First, new expressions for computing permittivities of the single-phase medium and the multi-phase medium were presented based on polarization mechanism. The expression for the single-phase medium such as soil kernel, water and air iswhile that for the multi-phase medium isComparing new expression with existing ones, it is found that the presented expressions have more explicit physical meaning and suit for various soils under various situations.Then the time domain reflectometry (TDR) technique was studied for measuring soil dielectric constant. Shape and dimension of probe will influnce measuring results. thus 3-rod tiny probe and 6-rod tiny probe were made for parallel tests. The experimental results show that the tested results of 6-rod probe are better than those of 3-rod probe.The finite difference time domain (FDTD) simulation for TDR system was also conducted, The simulated reflection curve agrees well with the measured one for coaxial cable transmission system and TDR system in the in homogeneous medium. Inflexion points of the test curve, with which the interface may be determined, can be simulated correctly for layered medium.Based on theoretical expression of soil electromagnetic properties and research on the TDR technique, a series of laboratory tests were performed for noncohesive soil and cohesive soil with TDR system. The influences of bound water on permittivity of soil were studied and the permittivity of bound water was computed based on Onsager function. The experimental results validate new expressions deduced in the thesis. It was proved to be feasible to in-situ measure pore ratio of saturated noncohesive soil and saturated cohesive soil with great pore ratio by availing the new expression for dielectric constant of soil for TDR system.Influences of electrical conductivity on soil dielectric constant were studied. It was found that electrical conductivity increases linearly with ion concentration, which is independent on ion type. So it is possible to in-situ measure contaminating concentration by the TDR system. The relationship between electrical conductivity and dielectric constant increment was also studied.On the basis of laboratory test and in-situ monitoring, the relationship between reflection curves and deformations of coaxial cable was studied. The sliding face can be determined correctly. The sensitivity and measuring range of cable are two important factors for choosing suitable cable.更多还原