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基于地质雷达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。分析结果为: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。
Based on the method of geological radar, the geological prediction of soft zone occurred in the process of deep diversion tunnel construction is carried out. Taking the dielectric permittivity of the soft soil with crushed-gravel soil as the research object, the relative permittivity value and the changing trend of the mixture of gravel-soil and mud were studied, and the empirical formula of the moisture content and the mixed permittivity was deduced. Band FDFD (finite difference time domain) forward analysis, analysis of its typical imaging laws and characteristics, so as to achieve the purpose of measuring the spatial location of the soft zone with the measured data. The results show that: the volume ratio of the gravel and soil mixture has a greater influence on the dielectric constant of mixture, the water body of the mixture has obvious reflection characteristics of the electromagnetic wave and is more likely to form multiple waves; by establishing FDTD model forward comparison The measured data in the tunnel can eliminate the multiple interference and correct the value of the water cut in the formation and establish the 3D slice diagram of the stratum, which can directly reflect the location of the water distribution in the stratum, thus providing methods and guidance for similar geological forecasting work.