다중채널 고해상도 터널 전방예측 탄성파 반사법탐사

Abstract

It is very difficult to select suitable geological research and geophysical exploration methods in tunnels constructed in hilly and mountainous areas, because geophysical and geological surveys and boring are very limited in pre-construction. This may lead that it is highly probable to encounter unexpected difficulties with poor geological conditions during tunnel construction. In this study, multi-channel seismic reflection exploration method at the tunnel face and portal was developed to anticipate and provide more detailed geological information of the geological disasters that frequently occur during tunnel construction. In order to obtain geological information directly in front of the tunnel, 96-channel 40Hz horizontal geophones were attached at the tunnel face in an interval of 0.2∼0.5 m. Also, clay and geophone mounts were used to increase the degree of close contact with the tunnel face. A total of four horizontal and vertical spreads were installed considering the tunnel face size and geological condition. For a CDP method sources were generated by air hammer, 1.5kg hammer, and shotgun at each geophone point. Seismic reflection data were recorded by 96-channel seismograph with 24bit A/D conversion. In the main data processing stage, digital filtering was applied to remove the low-frequency noise represented by tunnel-wave, and other on-site noise. In the final step, high resolution seismic reflection profiles were obtained through a pre-stack migration process. TSP results for the Goryeong 1 and Haengchi 2 tunnels, high resolution seismic reflection sections with depths more than 300∼400 m were achieved. These results were compared the results from face mapping and horizontal boring verified and a good agreement was obtained. This multi-channel reflection TSP(using CDP stack) is designed to obtain directly the geological properties ahead of the tunnel, which can be used to predict the geological risk factors (faults, fractured zone, water zone), and considered as a very cost-effective and expeditious method for seismic imaging ahead of a tunnel face.