Application of Cross-hole Seismic Tomography to Inferred Cavities Condition.

Abstract The construction of the Rajamandala hydroelectric power plant civil works has experienced critical problems that arise in implementation process, with occurrence cracks cavities conditions headrace tunnel locations. We applied cross-hole seismic tomography to detect important heterogeneities and mechanical proprieties formations between two boreholes this case inferred condition. source is inside borehole “a sparker” receivers “hydrophones” are an adjacent one, sparker lowered into one step at time. Seismic waves, propagating wall rock, spread widely, reflected refracted when encountering interfaces rocks different acoustic impedances. Reflected waves returning recorded. After processing first arrivals P we obtain a cross section velocities wellbores. With tomography, basis could be provided parameter adjustments guarantee safety. Our result shown there weak zone above low Vp (~1.2 km/s) may related (may fracture, unconsolidated fluid-filled rock or landslide caving). Checker-board resolution test also conducted determine tomogram areas reliable interpreted. challenges have poor due not enough raypath. Cross-hole can effectively safely guide excavation working surface combination reconstructed images technology.