Use of Seismic Reflection Surveying to Enhance Traditional Subsurface Exploration for Karst Evaluation

Geophysical surveying using the seismic reflection method was used to help determine zones of karstic bedrock and develop geotechnical parameters for design and construction of an elevated 400,000-gallon water storage tower at a site northwest of the City of Jackson, Missouri. The area was known to have karst topography. This history was used to develop a site evaluation program. Results of geophysical surveying were used to plan and prioritize subsurface exploration, including drilling and sampling. By combining geophysical and traditional drilling, the exploration was more cost efficient and effective than either individual element. Data from the seismic reflection survey, subsurface exploration and previous well drilling correlated well, indicating the southern portion of the survey area was generally more impacted by karst including the presence of irregular and pinnacled weathered rock and therefore avoided during site development planning. Highly variable bedrock depth and quality could adversely affect foundation design and construction. Therefore, QA/QC observation and testing were required to further assess rock quality at foundation locations. Overall, the exploration program helped identify comparatively higher quality bedrock, simplify design, and reduce overall construction cost and risk.