Seismic Investigation of a Deep-seated Mass Movement Assisting the Refurbishment of a Pressure Tunnel in Tyrol, Austria

The refurbishment of the Kaunertal hydroelectric power station, planned by the Tiroler Wasserkraft AG, requires a new water pressure tunnel crossing a deep-seated mass movement near the town Prutz in Tyrol, Austria. Preliminary studies including 2D and 3D refraction seismic surveys were carried out to determine the optimum trail of this water pressure tunnel. The tunnel should not be influenced by the mass movement and at best should run under the mass movement. Therefore definition of the deepest sliding surface of the mass movement but also the geotechnical condition of the moving mass was the main tasks of the seismic investigation. To obtain this information standard refraction seismology and refraction seismic tomography was applied. Because of high velocity structures near the surface the results of both methods are combined to construct the deepest sliding surface which was supported by the information of drillings and morphology, like the main scarps.