Application and analysis of wave-field and time-frequency characteristics of typical disaster-causing geological bodies detected by ground penetrating radar in the tunnel of Central Yunnan Water Diversion Project
The complexity and variety of disaster-causing geologic bodies in the tunnel of the Central Yunnan Water Diversion Project greatly increase the difficulty of interpreting the results of advanced detection.For this reason,based on the distribution characteristics and electrical parameters of the disaster-causing geological bodies,this paper establishes the theoretical models of three typical disaster-causing geological bodies,namely,caves filled with different media,water bodies,and soft-rocks,and then carries out the numerical simulation of the ground penetrating radar wave field and the research of time-frequency characteristics by adopting time-domain finite-difference forward modeling and the generalized S-transform improved based on S-transform.The ground-penetrating-radar wave-field is characterized by the following:arc-shaped reflection at the top interface of the karst cave,and the amplitude energy of water-filled karst cave is stronger than the air-filled karst cave;in the area of the water-bearing,there are several horizontal strong amplitude reflection events;in the area of the soft-rock,there are horizontal strong amplitude reflections on the interface of the soft-rock top and bottom;and the reflected waves from the top interfaces of water-filled caves,water-bearing bodies,and soft-rocks will have the phenomenon of phase reversal.The time-frequency characteristics of the ground penetrating radar signal are as follows:when the signal passes through the areas of the karst caves and water-bearing,its central frequency is concentrated in a low-frequency range;When the signal passes through the area of the soft-rocks,its central frequency distribution is more dispersed,and it is distributed in both high-frequency and low-frequency range.Based on four successful detection cases of the Central Yunnan Water Diversion Project,the wave-field,time-frequency distribution,single-trace signal,and power spectrum attenuation characteristics of ground penetrating radar real signals are consistent with their corresponding numerical simulation results,which confirms the reliability of numerical simulation results.The results of the study provide a scientific basis for the detection,feature identification,and prevention of typical disaster-causing geological bodies in tunnels,which is of great theoretical significance and engineering application value.
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