Study On Electromagnetic Properties Of Soil And Time Domain Reflectometry Technique

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.