Foundation Design and Site Development for a New Hospital over a Complex Karst System

Construction and site development for new facilities in the Corydon, Indiana area, typically involve treatment of one or more sinkholes, given the presence of the St. Louis-Ste. Genevieve limestone throughout this portion of southern Indiana. The site selected for the new Harrison County hospital included ten closed-contour depressions at the start of the project; site development activities disclosed five additional features. Foundation construction involved drilled piers bearing on competent limestone, with significant blasting required to excavate a walkout basement. Foundation construction encountered a highly variable upper rock surface, as well as a cave system with a flowing stream. Concrete placement in a number of the piers required creative field techniques, such as the use of dry cement to plug voids, to prevent flow of concrete into the cave system. Site development was accomplished using four of the features as drainage facilities for surface water runoff. One feature in particular was designed to receive runoff from 11 acres and was in close proximity to the stream in the cave system. The excavation for this drainage feature extended almost 40 feet vertically and the throat collapsed partially during construction. Special measures, including installation of oil-water separators, were employed to prevent contaminants, in the form of petroleum hydrocarbon residue from the parking lots, from reaching the sub-surface system.