Abstract:
On February 12, 2020, a large landslide occurred on US-231 south of Huntsville, Alabama. The slide completely severed the 4-lane divided highway, which is a major commuting route between Huntsville and communities south of the city. The Alabama Department of Transportation (ALDOT) was under significant pressure from the impacted communities to quickly solve the problem and reopen the road.
Dan Brown and Associates was engaged by ALDOT to evaluate the causes of the landslide and design a repair solution to reopen the road as quickly as possible. ALDOT’s solution involved removing most of the existing roadway to reduce loading and then spanning the slide area with twin bridges supported by foundations designed to withstand future slope movements.
Each bridge is seven spans of 135-ft long concrete girders. Each bent and abutment is supported by a pair of 9.5-ft diameter, permanently cased drilled shafts with 9-ft diameter, 14-ft long rock sockets drilled into limestone and shale bedrock. The shafts are reinforced with an 8-ft diameter (1.5-inch wall) steel pipe. Each pair of shafts is connected by a reinforced concrete grade beam for added stiffness.
A ShapeArray inclinometer is installed in each drilled shaft. Free-field ShapeArrays are also installed in the surrounding slope, supplemented by traditional inclinometers in the slope and vibrating wire piezometers to monitor groundwater levels. DBA and ALDOT have been monitoring the instruments since January 2021. The presentation will focus on the results of monitoring, including the response of the drilled shafts to shallow slides that developed between bridge bents as well as the response of the shafts to subsequent re-grading operations.