Multichannel Analysis of Surface Waves: Estimating Depth to Bedrock and Acoustic Properties in Karst Terrain

Conventional techniques such as boreholes and test pits have been used for geotechnical site investigation purposes for many years. These conventional techniques are invasive, time-consuming and expensive. To minimize costs and to complement intrusive investigation techniques, geophysical methods are now commonly employed for geotechnical investigations in karst terrain. One relatively new non-invasive geophysical technique is the active multichannel analysis of surface waves (MASW) tool. This paper explores the utility of using the active MASW tool in karst terrain. A 20-pound sledge hammer was used as an acoustic source; a Seistronix Ras-24 channel seismograph was used to record the MASW field data. MASW field data were processed with SurfSeis4 software; the output at each test location was a 10-layer shear-wave velocity profile of the subsurface. Borehole control and 2-D electrical resistivity tomography (ERT) data were used to verify and constrain the interpretations of the output 1-D shearwave velocity profiles. The results show that MASW can reliably be utilized to map variations in the engineering properties of soil/rock and to estimate depth to top of rock in karst terrain