Interstate Technical Group on Abandoned Underground Mines
Fourth Biennial Abandoned Underground Mine Workshop
Abstract: 3-D Seismic Tomographic Imaging for Abandoned Mine Subsidence Characterization Case Histories
Khamis Y. Haramy, Geotechnical Engineer
Matthew J. DeMarco, Geotechnical Engineer
FHWA Central Federal Lands Highway Division
Mining-induced surface subsidence can most easily be described as either a "trough" type deformation, generally resulting from full-extraction mining or widespread caving over failed pillar panels, or isolated "sinkhole" failures over collapsed near-surface workings. The classic trough-type subsidence occurrence is more easily accommodated on civil projects, with generally predictable angles of draw, areas of influence, vertical and lateral strains, curvatures and slopes. Sinkholes, on the other hand, are far less predictable in occurrence, often resulting in serious structural stability issues and public safety hazards. These types of failures are particularly difficult to characterize subsurface, especially where complex underground openings are involved and/or intervening overburden strata are present with high dissolution potentials. To this end, this paper focuses on the characterization of sinkhole failures utilizing the latest developments in 3-D seismic tomographic imaging - a technology similar in application to the medical CAT Scan. Three case histories are presented demonstrating deployment of this ground imaging technology, the types of void-fill-failed zones that can be detected, resolution qualities expected, and graphical outputs attainable. The case histories include:
U.S. Rte 24, Peoria, IL: 3-D seismic tomographic imaging of near-surface abandoned mine entries encountered during the installation of soldier piles along a retaining wall foundation. Included detailed mine opening and collapsed zone delineation.
SH 52 & I-25 Interchange, Denver, CO: 3-D imaging of potential sinkhole formation zone above old works located beneath planned bridge abutment and pier foundations. Included analytical assessment of sinkhole formation probabilities and drag on pile footings.
Leinster Nickel Mine, Western Australia: 3-D imaging of major sinkhole event over active mining operation, resulting in collapse zone approximately 200 ft across, extending to the mine workings nearly 300 ft below. Detailed characterization of failed volume and void conditions above the mine workings, as well as potential for renewed failure.