During the early stages of design, TTL was called upon to perform a geotechnical exploration at the site to evaluate the subsurface conditions and provide earthwork, pavement, and foundation recommendations. The exploration revealed the site is located in a heavily karstic area, meaning it is prone to sinkholes and other voids at or below the surface. Geologic maps of the site and surrounding areas show previous phosphate mining. Strip mining for phosphate often destroys the natural surface drainage patterns and leaves behind features such as large protruding pinnacles of bedrock, erratic piles of large boulders, deep excavated depressions, and wide furrows. These conditions were observed at the Columbia State site along with several natural and man-made sinkholes. TTL provided recommendations for repair of the sinkholes and depressions, as well as for the phosphatic soils on site. TTL also provided construction materials testing including earthwork and supervision of sinkhole repairs.
TTL’s use of a non-invasive method of subsurface exploration minimized borings, trenches, test pits, and other disturbances of the surface and subsurface. Phosphatic soils typically have a higher moisture content and are more likely to become unstable during construction. Minimizing pre-construction activities at the site kept the soil as stable as possible, especially considering the potential at the site for sinkholes, underground caves, and other natural and man-made depressions.
By being involved early-on in the design process, TTL was able to convey to the design and construction team the many challenges that might be encountered at the site. The firm’s geoprofessionals had prior knowledge of the area and the previous phosphate mining activities. Phosphatic soils can be very problematic and cause headaches during construction, especially if undetected until earthwork begins. At first pass to someone outside the profession, the site might have looked unusable. Instead, it is now providing 28 buildable acres for the higher education of Middle Tennessee residents.