Detailed geophysical survey was conducted on the rear wall of a sabo dam, which was damaged by a huge debris flow on July 9, 2014. The survey consisted of GPR and high-resolution seismic measurements for imaging internal fractures, along with photogrammetric image analysis for delineating surface displacements. A 10 m wide and 15 m high area on the wall face was covered with parallel lines at 20 cm intervals to map 3D subsurface fracture distribution using GPR. A single line was set at the bottom of the face for high-resolution seismic survey. Piezoelectric type accelerometers were pasted on the surface at 20 cm intervals and manual hit using rock hammer was employed for generating high-frequency signals. As a result, GPR could successfully imaged fractures at the shallow depths up to 1 m, and high-resolution seismic survey detected dipping fractures extending into the deeper portion of the body up to 8m. In addition, photogrammetric analysis clearly mapped blocked deformation. Combined interpretation of geophysical survey results with the photogrammetric analysis was helpful to interpret the dislocation process of the dam body. GPR and high-resolution seismic survey results also demonstrated their applicability for the delineation of internal fracture in large concrete structures. Read More: http://library.seg.org/doi/abs/10.1190/segj122015-050 |