A case study of seismic forward prospecting based on the tunnel seismic while drilling and active seismic methods

Abstract

Forward prospecting to predict the location of high-risk geological zones during tunnel boring machine (TBM) tunneling is important for safe and efficient tunnel construction. Seismic forward-prospecting methods are sensitive to geological structures and have been widely used in areas with relatively well-developed structures, such as mountainous areas with active tectonics. The Gaoligongshan Tunnel in Yunnan, China, with an advance pilot tunnel, was chosen for this study. The advantages of seismic while tunneling and active source methods for different detection distances were investigated, and the methods were combined to determine the geological conditions. An excavate geological study of the tunnel had identified fractured zones ahead of the tunnel face. Our seismic prospecting results were basically consistent with this conclusion. On the basis of these data, the excavation rate was slowed and tunnel support was increased; excavation through the area was then able to proceed without incident. The presence of a pilot tunnel was found to create interference in the seismic signals. We modeled this effect with numerical simulations. On the basis of the results, we discuss appropriate observation systems for use in tunneling projects with pilot tunnels. We demonstrate that seismic signals received by geophones coupled to the wall further from the pilot tunnel reflected the geological conditions for both seismic while tunneling and active source methods. The seismic source should thus be placed on the tunnel wall further from the pilot tunnel to improve results.