Depth to Bedrock

Depth to bedrock can be a critical parameter in geotechnical investigations.  Bedrock influences the stability of structures built above it, particularly in earthquake prone areas, and its depth can strongly impact initial construction costs based on rippability and excavation volume.  Shallow bedrock can be a benefit where solid foundation shoring is needed and minimal soil removal is required.  Deeper bedrock can be a liability where lateral variations in soil characteristics are present which can cause footing and slab failures if not accommodated.  Do you know how deep bedrock is beneath your site?

Knowing the depth to bedrock  is a critical parameter in geotechnical investigations as bedrock influences the stability of structures and  transport of  contaminants as they travel down gradient on bedrock surfaces.

One of the most common geophysical methods for depth to bedrock determination is refraction seismics .  This is a non-invasive, easily deployed method that provides quantitative information about the spatial variability of depth-to-bedrock as well as producing quantitative information about the strength of bedrock through the use of acoustic velocity as a surrogate for rock density.  Confirmation augering or drilling will always be required to “calibrate” seismic results, but, far more area can be covered with seismics in a much more affordable manner compared to drilling costs to cover the same area.

Depth to bedrock is also important in placer mining where paleo-channels eroded into bedrock are sought.  Quick coverage with refraction seismics can provide maps of channels which help focus dredging and excavation on the high-pay zones.

Depth to bedrock seismic refraction profile across a canyon - hydrogeophysics Image

Depth to bedrock seismic refraction profile across a canyon.

Environmentally, knowledge of depth-to-bedrock in areas of historic spills will help in the mitigation stage by quantifying excavation volumes of contaminated material.  Knowing the depth to bedrock also facilitates the understanding of fate and transport of  contaminants as they tend to travel down gradient on a bedrock surface.

For more information on refraction seismics go here.