Magnetotelluric characteristics of hazardous hydrothermal geological structures at railway tunnels—A case study of Chaluo Tunnel of Sichuan-Tibet Railway

Abstract:

Taking the magnetotelluric behavior of the adverse hydrothermal geological structures at Chaluo Tunnel of Sichuan???-Tibet Railway as the research object， and with magnetotelluric multi-psite， multi-frequency tensor decomposition， this paper distinguishes the statistical rose diagram of the geo-electrical strike， frequency-based cloud maps， site-based cloud images and structural dimension parameters， and then uses fine two-dimensional inversion technology to infer the geological structure characteristics， and to image the adverse geo-structures. The purpose of geo-structure imaging is to provide geophysical reference for route selection for the Sichuan-Tibet Railway tunnel. The conclusions are as follows： the Geotectonics at the proposed tunnel is of strong two-dimensional nature； therefore， it is suitable to carry out two-dimensional magnetotelluric sounding as a means of tunnel hydrothermal investigation. With characterization of the geo-structure in the study area， the mechanism of the deep geothermal migration mode of the hot spring group in the study area is deduced， while the possibility of the thermal hazard affecting the construction of Chaluo Tunnel is very small， with only some potential water damage in the position where the fault of Zamagang-Maoyaba passes through the tunnel.

Key words:tunnel;magnetotelluric;impedance tensor imaging;two-dimensional inversion;hot damage;water damage;Sichuan-Tibet Railway