A modified seismic reflection approach for engineering geology investigation in fractured rock zones

摘要

Delineating soil/rock interface is critical for geotechnical and tunnel site investigations in engineering geology. In Singapore, we also need to draw attention to local faults and fractured rock zones because the regional geology of Peninsular Malaysia and Singapore contains some minor, steep and brittle faults propagating at some areas in the island city. In addition to drilling boreholes, seismic reflection survey is a viable option to mitigate the uncertainties in areas without boreholes. However, the current practice of seismic reflection still follows the methods used in the petroleum exploration community. This investigation reviews and modifies the seismic reflection approach specifically customized for geotechnical and tunnel site investigation, which is partly different from petroleum exploration. We demonstrate the modified approach through a field testing in Singapore. The resultant image from the field test fairly captures the soil/rock interface, and it is validated based on the vertically drilled boreholes. A local fault or a fracture rock zone is also identified in the migrated image. The extent and location match with the record of horizontal directional coring (HDC). This addresses the concern of fracture rock zone raised from the regional and local geology and provides useful information for geotechnical and tunnel engineers. In addition, we further discuss the general challenges of using the modified seismic reflection approach. This work aims to help the geotechnical and tunnel community better understand the noninvasive seismic reflection survey.