GPR Investigation of Mine Subsidence Hazards in Charlotte, North Carolina
North Carolina gold mines were a leading part of the minerals infrastructure in the 19th and early 20th centuries. Although production from registered mines was monitored by regulation, detailed maps of surface operations and underground access networks exist for only a few of the larger mines. When the mines ceased operations, land was sold for agriculture and ultimately for commercial and housing development. Shafts in some mines may have been backfilled, but it appears that stopes and some drifts may have been abandoned as is. Roof supports in drifts were typically large timbers and lumber. Some drifts were excavated to within a couple of feet of the ground surface. Since abandonment, settlement, ground water flow, and timber rot sometimes lead to collapse of near-surface voids and formation of sinkholes. Subsidence appears as rectangular depressions or conical collapse funnels. We investigated a potential mine collapse under the foundation of an urban Charlotte home to explain the relationships between the shallow subsurface geology and the origins of and hazards associated with the sinkhole. The home is near the approximate location of the historic Chinquepin Mine. Abandoned structures from the mine burned in 1895. To search for uncollapsed voids, we conducted a GPR survey on the bare earth basement floor with 400 MHz and 100 MHz antennas and also a 400 MHz reference survey in an adjacent grassy field. 3D models show several void-like features in the subsurface, one connecting to an open sinkhole. Data from the neighboring grassy field also reveal characteristic anomalies of partially filled voids. The home and neighboring area are built over remnants of mine excavations, and because ground subsidence has already occurred over part of these excavations, we suggest that future sinks of similar magnitude may occur.
My name is Emma Heavener and I am an undergraduate geology student at UNC Charlotte graduating in January 2020. My main interests are geochemistry and igneous petrology. Paleontology is also a great love of mine. I first encountered geology while attending Appalachian State University. I was a history major taking Historical Geology to fulfill a gen-ed requirement. I converted to geology at the end of that same semester. In my free time, I love to study thin sections, read, and learn new things. I serve as president for a student organization on campus called Ratio Christi. I am currently working on an independent study centered around coal ash ponds contamination and investigating Charlotte terrane rocks as potential hosts for leachable heavy metals. A fun fact about me is that I speak (not fluently by any means) French, Spanish, American Sign Language, and very little Japanese. I love languages and aim to be fluent in these by my 30th birthday. Learning is greatly fulfilling for me and I am constantly looking for new things to discover and understand.
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