Abstract: At present, a large number of railway and highway projects select the long and large tunnels passing through the mountainous areas with large topographical variations and complicated geological conditions. Under the tight construction schedule, if only traditional exploration methods such as engineering geological surveying and mapping as well as exploratory drilling are used for the geotechnical investigation of long and large tunnels, it is difficult to accurately characterize the engineering geological and hydrogeological conditions of the proposed tunnel in a short period of time and provide detailed and adequate engineering data for the design and construction of the tunnel. This article presents a long mountains tunnel in the northwestern region as an engineering case history. To quantify the geological conditions of the proposed tunnel, comprehensive investigation methods for the data collection, such as, remote sensing interpretation, engineering geology mapping, geophysical exploration, deep and shallow test boring drilling, hydrological testing and comprehensive logging, are used in the explorations. Such comprehensive exploration methods significantly improve the characterization of the soil and rock lithology, structural distribution and characteristics, hydrogeological conditions, etc. in the tunnel project site, and obtained relatively accurate geological data. The project proved that the comprehensive investigation method combining the above-mentioned multiple exploration methods could obtain technical, social and economic benefits of improving the construction schedule, reducing the amount of exploration and cost saving through the comprehensive analysis.

Key words: Long and Large Tunnel, Comprehensive Geological Investigation, Comprehensive Geophysical Exploration, Remote Sensing, Application