Stabilization of Deep Slope Failure with Drilled Shafts: Lake Ridge Parkway Station 248; Grand Prairie, TX

Lake Ridge Parkway was constructed in the early 1980s with earth fill embankments to raise the roadway grade above the reservoir level of the newly constructed Joe Pool Lake in southern Dallas and Tarrant counties, Texas. The embankments were constructed of residual Fat Clays of the Eagle Ford geologic formation, which were the only locally available soils. Over the ensuing years the embankments began experiencing shallow slope failures which began impacting the roadway pavements by about 2002. The shallow failures were investigated and subsequently repaired with Fiber-Reinforced Soil (FRS) in two phases completed in 2004 and 2007, respectively. During construction of the shallow slope failure repairs a much deeper slope failure was discovered in the vicinity of Station 248. Subsequent deeper site exploration detected a slow moving "creep" type failure mass sliding along a very soft bentonite seam within the underlying shale. The slide was repaired with 0.9-m (36-inch) diameter drilled shafts. The required capacity and spacing of the drilled shafts were determined with limit equilibrium methods and the shear, moment, and deflection of the shafts were determined using the "p-y" design approach for laterally-loaded drilled shafts. Construction of the deep slope failure repairs was completed in early 2010. The site history, exploration methods, design methodology, and construction activities are presented for the deep slope failure repairs.