GPR Forward Modelling and Imaging Analysis for Boulder Detection: Fid-Bau Portal

GPR Forward Modelling and Imaging Analysis for Boulder Detection

Dai, Zhiheng / Zhang, Mengxi / Gu, Jie

Boulders are incompletely weathered and “nearly spherical” granite, which widely distributes in fully weathered granite strata. If a tunnelling shield machine is driving in fully weathered granite strata, it frequently encounters boulders. In such circumstances, the cutter heads usually get stuck and the body of tunnelling shield machine is damaged by boulders. Therefore, it is highly essential to detect the boulders before tunnelling through the face. To accurately obtain the location and size information of the boulders, the ground-penetrating radar forward modelling and imaging analysis in boulder detection were conducted. First, a series of forwarding modelling was carried out to demonstrate the influence of boulder size and burial depth on the reflection curves. Then, the reflection curves caused by boulders were characterized, which was proved to be hyperbolic curves. Second, imaging analysis was set up to determine the location and size information of boulders. Based on the principle of portable ground-penetrating radar, the theoretical calculation method was derived for determining the reflection points. Comparing the numerical analysis results, the rationality of the theoretical method was verified. Subsequently, by evaluating the inverse of the theoretical calculation method, the imaging method to determine the location and size information of boulders was derived. In the end, an example was used to examine the accuracy of the imaging method. In a word, the imaging method could accurately determine the boulder size and location information from the ground-penetrating radar detection result, which provided a reliable basis for boulder treatment and disaster prevention.