At ash hill in Kitami City, Hokkaido, where some concrete pile driven in as end-bearing Pile for a reinforced concrete buildings. By doing so several concrete pile (HSA, σc=92kg/cm², φ=30cm) broke in the middle of the basement site. I was asked to investigate the cause of the damage of the piles, so I did many mechanical testings and geological examinations in the ash. The compression strength test indicated some pumices and hard clay layer in the ash, but their strength were weaker than the concrete piles allowable strengths.
Therefore was done a seismic refraction investigation at this ash hill basement (diabase). First was comfirmed the position of the basement site by boring, and after the basement was beaten by heavy weights (63.5kg), so that seismic refraction waves were recorded in detectors at the ground surface.
By analysis of the travel time-distance cauve, under the ground surface was found an unregularity in rise and fall topgraph, may be the concrete piles broke at a rise position in basement.
This seismic refraction method may be usefull in other field of basement investigation.