Mapping bedrock is important for many reasons, from determining the type of equipment needed for an excavation project to estimating the amount of material to be extracted from the earth. Bedrock depth profiling or mapping can facilitate balanced grading plan designs, allow rock excavation volume estimations, aid in proper pre-mobilization excavation or drilling equipment selection, provide data on soil and rock mechanical properties, delineate buried valley bases for well siting, and detect karst-related bedrock depth variations.
Seismic refraction is typically the best method for shallow depths of less than approximately 100 feet. At greater depths, or in marine or water-saturated environments, seismic reflection may be a better choice. Where boreholes are available, hole-to-hole or hole-to-surface seismic tomography data can also be collected to improve the resolution of either seismic refraction or reflection surveys.
In some situations, it may be preferable to perform bedrock depth profiling or mapping using microgravity measurements or electrical imaging. Microgravity measurements are sensitive to the subsurface mass distribution and can discriminate between locations underlain by dense rock at shallow depths, and those where there is a significant thickness of less dense sediments. When electrical imaging is used for rock depth profiling, it is important to remember that this method is sensitive to variations in electrical conductivity of subsurface materials. Neither microgravity nor electrical imaging methods can provide the elastic parameters and rippability information available from seismic data.
Upon site assessment, RETTEW/Enviroscan will provide recommended options for a specific project and circumstances.