In a shallow-buried and soft surrounding rock road tunnel, landslides in working face frequently occurred. It is necessary to timely explore the geology in front of the working face such as litho-logy, moisture content and so on. Ground Penetrating Radar can forecast the moisture content in the tunnel construction. In this article, we focus on the analysis of attenuation mechanism of electromagnetic wave in the moist red clay, and establish a mathematical model. By means of large amount of lab experiments, the relation of moisture content and dielectric constant of the red clay has been discussed. A new way of fitting the theoretical formula of red clay to eliminate the errors in data processing is presented. Finally, the results of excavation construction of tunnel in Henan verify the rationality of the curve. Consequently, it can be provided reference material and an extended example for similar project.
Accurate determination of moisture content is very important for the tunnel stability in construction processing of soil tunnel [1]. The change of soil moisture content in tunnel not only affects the strength and deformation characteristics of the soil sample, but also will directly influence the stability of tunnel, surface subsidence, groundwater flow and so on [2]. Therefore, monitoring moisture content timely is of important significance to surrounding rock or soil [3]. At present, the commonly used determination of moisture content in the soil is drying method, neutron scattering method,Y-ray method and time domain reflect-meter (TDR) method [4–5]. However, these methods in the application of tunnel have various deficiencies, such as narrow scanning area, complicated handling and so on [6–7]. Searching for a fast and efficient method of measuring soil moisture content becomes a hot spot in research. In recent years, ground penetrating radar (GPR)which acts as an accurate detection method in estimating moisture content of meso-scale rocks. It is widely applied in highway and railway tunnel [8]. GPR which is based on the electromagnetic properties in mediums, and reflects the near-surface soil moisture content through the change of dielectric constant and velocity of electromagnetic wave between two media. Comparing with other measuring methods, GPR method exhibits the advantages of the large-volume sampling, fast measurement speed, high resolution, nondestructive, etc. [9]. Therefore, GPR puts up a bridge between small scale and large scale measurement in soil moisture content [10]. But how to use the echo signal of GPR to deduce the unexcavated geology and moisture content in the front of working face in tunnel construction, is hot spot problem in general research [11].
