Detecting Potential Seepage Paths in Bakhtyari Dam Site using Seismic Tomography

Seismic travel time tomography uses seismic waves to image velocity distribution inside the ground. This method has been widely applied to practical applications in many fields including earth sciences. In this method, first-arrival times of seismic waves due to artificial sources, observed at receivers in the vicinity of the exploration target are analyzed to obtain the velocity distribution within the propagation area. This paper describes the seismic tomography investigation performed at the abutments of Bakhtyari Dam site. The study aimed to find the low-velocity zones that may correspond to jointed media where seepage most likely happens. We performed 3-D tomographic inversion on Bakhtiari dam seismic data. To perform ray tracing and travel-time computation at each iteration, we used Um and Thurber (1987) method and for inversion step we used SIRT method. In most of the tomograms, average velocity was 3km/s. According to the Barton relation (2006) the seepage potential in dam sit abutments, is low. A low velocity zone has been detected above the 690 m level in right abutment. It shows that the weak zones extended from surface down to this level. Despite the presence of some weak zones, the rock mass quality is good, and the design of the grout curtain could help to bypass the reservoir water away from these seepage paths