GRAVEL SOIL MIXTURE DIELECTRIC CONSTANT RESEARCH
AND FDTD FORWARD OF WEAK ZONE IN TUNNEL
SU Lihai1，2，LI Ning1，LV Gao1，GUO Bingxuan1
(1. Institute of Geotechnical Engineering，Xi?an University of Technology，Xi?an，710048，China；2. Engineering Institute，
Air Force Engineering University，Xi?an，710038，China)
摘要基于地质雷达(GPR)方法对深长引水隧洞施工过程中出现的软弱带进行地质超前预报。以软弱带碎石泥土的混合介电常数为研究对象，研究碎石泥土混合体的相对介电常数值及变化趋势，推导含水率与混合介电常数经验公式及关系曲线；通过对2种软弱带的空间分布情形进行FDTD(Finite Difference Time Domain)正演，分析其典型成像规律及特征，从而达到以实测数据推算软弱带的空间位置的目的。分析结果如下：碎石及泥土混合体的各成分体积比对其混合介电常数影响较大，混合体的水体对电磁波的反射特征明显并更容易形成多次波；通过建立FDTD模型正演对比隧洞内实测数据排除多次波干扰，修正地层含水率取值并建立地层三维切片图，可直观体现地层含水分布位置。从而对类似地质预报工作提供方法和指导作用。
Abstract：It?s important to implement advance geological forecast for Weak zone in a long diversion tunnel construction by GPR. This paper take gravel and clay mixed dielectric constant as the research object，and study on the relative dielectric constant of shale and water mixture and its trend. Then we deduce the experience formula and the relation curve moisture content of the mixed dielectric constants. Therefore we make FDTD(Finite Difference Time Domain) forward modeling by means of two kinds of spatial distribution of weak zone，and analyze the typical imaging regularity and characteristics. So as to we may achieve the purpose of the space position in the weak zone from the measured data. Analysis results as follows：The volume ratio on the mixing soil and gravel mixture component have great influence on the dielectric constant. Meanwhile the water content reflection characteristics of electromagnetic wave are obvious and easily reform to multiple waves. In consequence we can remove interferences through the measured and FDTD forward. And we fixed formation value of moisture content and establish the 3D slice result maps. Which provide method and guidance for similar geological forecast projects.
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2015, Vol. 34 
