Application of seismic tomography for detecting potential seepage paths in Bakhtyari Dam, Iran

Bakhtyari Dam and Hydropower Plant Project is one of the largest hydroelectric projects in Iran. This dam is located in Lorestan, in southern Iran, on the Bakhtyari river, which is a headstream of the Dez River. Previous gallery surveying showed that some open joints were present in the abutments. These joints may act as a good conduit for seepage. Five galleries were used to carry out seismic tomography in the right and left abutments (GR1, GR2 and GR3, GL2-GL3, totally 765 m). The objective of the tomography was to detect these weak zones susceptible for seepage. Velocity images obtained by P-wave travel time tomography indicated that in the level of GR2 gallery upward there is a large zone of low velocity. But the rock mass quality seems better in the left abutment. In spite of unfavorable condition in R₂₃ block (GR2-GR3), the P-wave velocity between GR2 and GR1 galleries is in the range of undisturbed limestone. Despite the presence of these weak zones, the placement of the dam is where 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.