Solutions for a complex world: Void Detection & Location
Article by: Shawn Calendine | hydroGEOPHYSICS
The existence of voids in the subsurface can lead to significant ground surface failures and can pose a severe hazard for structures and people on the earth’s surface. Voids can develop due to natural processes, such as subsurface erosion, dissolution, and other geological processes, or are created by human activity through subsurface mining, tunneling, or the presence of infrastructure, such as tanks, vaults, basements, and piping. When the extent or size of these void spaces is unknown, they can present a significant risk. Voids can cause subsidence or collapse, resulting in damage or destruction of property and loss of life, or create conduits providing pathways for pollutants to contaminate vulnerable water resources.
The extent or size of unknown void spaces can present a significant risk.
Geophysical methods are widely used for void detection and provide non-destructive, economic, and rapid targeting to determine the size, depth, and orientation of void structures. The choice of geophysical methods for void detection is dependent on site characteristics, soils, geology, and dimensions and depth of the targets. These factors can vary widely, and the use of multiple technologies may be required to produce the highest quality target information.
Hydrogeophysics (HGI) has over 30 years of experience in providing void detection surveys at differing scales and site conditions. Microgravity, seismic, ground-penetrating radar, and electrical resistivity are methods used in mapping targets such as mine workings, tunnels, karstic features, near-surface voids, and large washouts. Seismic surveys can include reflection, refraction, and surface-wave methods. HGI’s innovative approach to void mapping allows us to detect and delineate voids for a broad range of industries, such as mining, environmental, engineering, natural resource exploration, and oil and gas.
Geophysical methods are widely used for void detection providing non-destructive, economic, and rapid targeting determining size, depth, and location.
HGI performed a seismic survey coupled with a GPR investigation at a gold mine in North America to understand historic mine workings suspected to underlie a mining haul road. The primary concern was a recently discovered shaft. Visual inspections suggested the shaft appeared to strike an orientation extending directly beneath the haul road. The objective of the geophysical investigation was to confirm whether the historic mine workings extended under the haul road and determine the depth and trends of any void spaces that may be hazardous to site operations.
The seismic and GPR results identified several features that correlate across several survey lines.
In 2014 HGI used electrical resistivity at Kartchner Caverns State Park to understand the extent and orientation of natural voids in the park. The electrical resistivity method considers subsurface conditions and materials determining physical and mechanical properties evaluating the size and stability of the subsurface conditions. The Kartchner Caverns State Park electrical resistivity profile below shows voids as dark brown and black shaded areas, and the more competent karstic rock surrounding the natural caverns.
About the Author: Shawn Calendine | hydroGEOPHYSICS
Shawn Calendine is the Marketing & Development Manager at hydroGEOPHYSICS (HGI). Since joining HGI in 2005, Shawn has worked in many positions for HGI, most notably, as a team member managing the leak detection and monitoring (LDM) program for nuclear waste tanks at the Hanford Site in eastern Washington State. Following the LDM program, Shawn moved into field geophysics, gaining high-level experience with HGI’s geophysical technology toolbox.
In addition to work as a marketing consultant, Shawn participates, as a board member for several industry-related nonprofit organizations and authored several papers on geophysical methods relating to liner leak location and resistivity characterization. Over the past 15 years, Shawn has presented on geophysical topics more than 30 times at professional meetings and conferences. Shawn holds Bachelor of Science degrees in both Environmental Science and General Science with a minor in Biology from Portland State University.
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