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. ALDOTâ€ÂÂs solution removed most of the existing roadway to reduce loading and then spanning the slide area with bridges supported by foundations designed to withstand future slope movements.
Each bridge is seven spans of 135ft concrete girders with a concrete deck. Design was completed for the bridge and a contract awarded to the contractor about 3 months after the slide occurred.The bridges were open to traffic less than 5 months later and 2 months ahead of schedule.
The bents and abutments each have a pair of 9.5ft diameter, permanently cased drilled shafts with 9ft diameter, 14ft long rock sockets drilled into limestone and shale bedrock. The shafts are reinforced with a 8ft diameter (1.5inch wall, 60ksi) steel pipe. The pair of shafts is connected by a reinforced concrete grade beam for added stiffness. A.H. Beck was the drilled shaft contractor, completing all 36 shafts 1 month ahead of schedule.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. ALDOT will monitor displacement of the shafts and free-field slope movement. Action levels have been developed for shaft displacement and slope movement to guide ALDOT response actions to either occurrence.