The True Hurts

Case Studies
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In the 1960s, designers planned for the interchange at I-240 and I-40 in Memphis to be a true interchange—the traffic on I-40 continuing on through the city’s Overton Park area. As work began the Overton Park route was abandoned, leaving the interchange as the only route for commuter and commercial traffic around and into the city.

This interchange was a merging mess of sharp turns and cloverleafs, proving dangerous and sometimes deadly over the past 20 years. The state realized that the interchange needed a complete overhaul to improve traffic flow and commuter safety. A major reconstruction project was approved in late 2004, scheduled for completion this year.

This $94 million project required 22 new MSE walls for grade separation. During this phase, the weak subgrade beneath four walls was improved using the Geopier Rammed Aggregate Pier (RAP) System . The walls ranged in height from 15 to 25 ft and in length from 150 to 1,600 linear ft. Applied contact pressures under the new MSE walls ranged from 3,000 to 5,000 psf, exceeding the allowable bearing capacity of the soil. Over-excavation and replacement or subgrade improvement would be necessary to provide adequate factors of safety for bearing capacity and global stability. The Geopier RAP System was chosen after it was determined that undercutting the required 10 to 16 ft would result in unacceptable temporary slope stability.

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