KENTUCKY KARST
Figure 5 - The Dishman Lane Collapse was caused by loads imposed over a large cave passage. The collapse, resulting in a bedrock collapse sinkhole, opened up in February 2002 (Crawford 2002).
4). Primitive uses for the cave included piping into the underlying passageways as septic tank dump stations and public landfills. Greater knowledge of the cave and concern for its ecosystem exists today and has resulted in more conserva- tive developmental endeavors designed to protect the cave and its environment.
Two significant bedrock collapses have occurred within the city limits of Bowling Green, in 2002 and 2014. A third construction equipment-induced collapse occurred in 2016.
According to an investigation report (Crawford, 2002), in February of 2002 a large collapse occurred on a portion of Dishman Lane at its intersection with Mill Valley Road, a newly constructed section of road. The 45m wide sinkhole collapsed into the main passage of State Trooper Cave, lowering the road sur- face 5m (Figure 5) (Waltham, Bell, and Culshaw 2005).
Before the road was built, a site inves- tigation led by Crawford used micrograv- ity testing to detect the State Trooper Cave passages along a proposed route for Dishman Lane (Crawford 2002). The testing showed that the proposed route would be built directly above a large collapse room in the cave. Further investigation showed the broken rocks associated with collapse extended all the way to the surface, indicating a surface collapse was possible (Crawford 2002). The road was still built on the proposed path, and the collapse was due to exac- erbation of pre-existing rock instability by 20 years of additional stress due to
Figure 6 - A sinkhole formed under the Skydome at the National Corvette Museum February 12th, 2014. Construction of the muse- um created an imposed load over an underlying cave passage, caus- ing the weakened cave roof to collapse (Polk, et. al. 2015).
significant urban development. All the storm drainage in the area had been directed into smaller sinkholes that were also engulfed by the collapse of the cave roof. There were no injuries, but the catastrophic collapse into the passage directly beneath Dishman Lane led to nine months of repairs costing a million dollars. The Dishman Lane collapse exhibited features of bedrock collapse and soil failure (Waltham, Bell, and Culshaw 2005).
In February 2014, a sinkhole opened up at the National Corvette Museum in Bowling Green, Kentucky. The floor of the Corvette Museum Skydome col- lapsed into an underlying cave system, creating a 9-meter-deep sinkhole and swallowing eight corvettes. The under- lying cave is about 67 meters long and 12 meters wide with an average depth of 20 to 26 meters (Figure 6). The bed- rock consisted of thinly interbedded limestone and chert between two impure limestone units. Talus and breakdown, the debris resulting from the collapse, are common on the floor of the cave in which the sinkhole formed, providing further evidence for a lack of long-term structural integrity of the bedrock in the area. The results of an investigation of the collapse revealed that the collapse occurred because of the failure of the cave’s roof which is made up of thinly bedded and impure limestone (Polk, et. al. 2015).
Another cave, By-Pass cave, which is hydrogeologically connected to the Lost River Cave System is approximately 5
Figure 7A - By-Pass Cave rests at shal- low depths under Bowling Green, making it extremely vulnerable to collapse. After digging into the cave roof, the exposure was temporarily fixed with a thin layer of concrete. This concrete will contribute to a decrease in roof stability, making the cave at higher risk for future collapse.
Figure 7B - By-Pass cave is at less than approximately 5 meters depth. The cave is shallow enough that cars can be heard as they travel overhead on Nashville Road.
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