Abstract:The newly built Chizhou-Huangshan Railway is a high-speed railway dedicated to serving the tourism industry, with a tunnel ratio of more than 60%. The railway is designed with several long tunnels , of which a tunnel is 8986m in length and the maximum height difference between the tunnel body and the surface is 775m. It is difficult to achieve this depth for general prospecting methods. Besides, the geological conditions along the tunnel are extremely complicated because of the intense cutting of the topography, the changeable landforms, the well-developed fault structures and the numerous underground rivers. Audio magnetotelluric sounding method has the characteristics of large detection depth, high resolution to low resistivity and low construction cost. It is light in equipment and good in passability. At present, it has become the main method used in the investigation of long and deep buried tunnels in mountainous areas at home and abroad. This paper introduces the working principle, field technology and data processing flow of audio magnetotelluric sounding method, and expounds the practical application effect of this method in the investigation of the tunnel. The field data acquisition accuracy of this audio-magnetotelluric sounding work is high and the data processing method is appropriate. The distribution of strata along the tunnel and the characteristics of adverse geological features, such as fault are basically identified. The inferred results are in good agreement with the drilling results, and the expected tasks are successfully completed. Based on the geophysical results, the formation integrity is evaluated and the surrounding rock of the tunnel is classified and delimited. It provides a reliable geophysical basis for the next tunnel construction, and also plays a certain reference role and reference value for similar work in the future.
