oa Integration of Seismic Surveys to investigate an Abandoned Mine Site

The near-surface rock structure (about 50m thick) that covers an abandoned marl mine nearby the small village of Montevecchia (Italy) was investigated through a combination of seismic surveys. the mine was abandoned in 1958, after a massive collapse that involved all mine levels causing a large sinkhole on the top of the hill where the mine is placed. the seismic experiments had to be performed outside the mine because, at present, nearly all mine levels are flooded. the only accessible gallery is the upper one, but its direct inspection is considered unsafe and limited to a small section.<br>the methods selected for these Investigations were Refraction Seismics and Multichannel Analysis of Surface Waves (MASW). in addition, a sort of transillumination experiment was tried by posing two geophones inside the mine at the entrance of the upper gallery while the seismic source was moved along the road above the mine. All the methods were successful and gave complementary Information. Refraction seismics was used to characterize the upper low velocity layer and the second layer of the near-surface structure. the MASW method was necessary to assess the existence of a velocity Inversion revealing the presence of a low velocity layer trapped between the 2nd layer and a 4th high velocity layer covering the upper mine gallery. the transillumination experiment validated the presence of the 4th layer and gave an estimate of the average velocity that represents a lower boundary for the P-wave velocity within this layer. All the methods were also consistent in indicating the areas where the rock structure is more affected by fractures and discontinuities. Finally, both refraction and transillumination data were analyzed to derive average estimates of attenuation level and rock quality factor.