Use of Geophysical Methods in Predicting Geologically Hazardous Zones for Railway Express Tunnels

Abstract

Tunnel excavation is always extremely risky in rocky mountain areas. Falling rocks and flooding are the main threats to the safety of the tunnel. Accurate geological prediction could save the tunnel from great damage. Many geophysical exploration methods have been used to investigate geologically hazardous zones, such as fault lines, fracture zones and cave at the excavation site (Alimoradi et al. 2008). Compared to percussion drilling and core drilling, geophysical methods have more advantages, such as a longer exploration range and quicker measurement and evaluation time. In China, tunnel seismic prediction (TSP) was first introduced in the early 2000s, and has become one of the most important prediction methods of geologically hazardous zones (Liu 2001). However, the precision of its results could be degraded due to the non-uniqueness problem of a single geophysical method. Various kinds of geophysical methods, such as DC resistivity, transient electromagnetic (TEM) and ground penetrating radar (GPR), can also be used for the prediction of geologically hazardous zones. A combination of resistivity, core drilling and logging was used to investigate the geological characteristics and possible construction of a railway tunnel, and logging confirmed the resistivity imaging results (Dahlin et al. 1999). TEM imaging has been used to explore the water-bearing bodies located ahead of the tunnel excavating face because it is sensitive to water-bearing objects (Xue and Li 2008). A technical system for reliable prediction, including TSP, GPR and TEM methods, has been developed by analyzing the advantages and disadvantages of these geophysical methods (Li et al. 2010). Integrated interpretation can minimize the risk of geological hazards.