Site Characterization and Geotechnical Roadway Design over Karst: Interstate 69, Greene and Monroe Counties, Indiana

摘要

Interstate 69 is currently the largest new interstate highway construction project in the United States and is located in southwest Indiana. Twenty-three miles of the interstate traverses karst terrain consisting of sinkholes, swallets, caves and sinking streams. Geologic and hydrogeologic mapping beyond the conventional geotechnical test boring investigations were required to determine karst treatments. Environmental and water resources were additional concerns for this environmentally sensitive karst system. Bedrock structure and stratigraphy for the karst aquifers were essential for evaluating a variety of mapped and buried karst features across multiple and transitioning physiographic areas. Characterization of the karst aquifer was essential to understanding the hydrology of mapped and unknown karst features. The upward extending cave stream or karst flowpath is better understood knowing its stratigraphic interval and interpretation of hydrogeologic mapping. Results from dye trace studies assisted in developing engineering solutions and determining the environmental impacts of roadway construction. Dye trace injection sites included sinkholes, sinking streams and karst voids. Additionally, some fractures encountered during geotechnical borings were also injected. Geotechnical engineering efforts addressed the basic principle regarding engineering in karst, which is recognizing that water drives the karst process. A significant aspect for deterring sinkhole development is understanding and controlling surface and subsurface water, as evidenced by case histories. Applying these concepts, engineering solutions consisted of an aggregate cap to allow water flow in a sinkhole but minimize sediment transport; a concrete cap to minimize water infiltration into the sinkhole, and the use of geomembrane liners to minimize surface water infiltration into known areas of concern.