Gregg Matlock, project engineer with Sandman Structural Engineering in Brainerd, MN, had worked with tire-derived aggregate (TDA) once before when he recommended it as a possible solution for the future site of Concorde Flats, an affordable senior and market-rate apartment building in Burnsville, MN.
Matlock had a couple of challenging issues to address at the building site. “There was a severe imbalance of soil at the site,” Matlock explained. “One side had two stories and the other had none. The lateral pressure induced by that soil basically made it so we couldn’t resist it without using an alternative backfill that would reduce the pressure on the building.”
From his experience, he knew TDA could be the alternative backfill material. Add to that, the TDA had to cooperate with another part of the design—a 20-foot-tall retaining wall on another side of the building that would abut to the TDA.
TDA wasn’t a slam dunk. Sandman Structural Engineering, the engineer of record on the project, offered two choices to the contractor, in addition to TDA. A geo-grid system was quickly dismissed because of building site constraints. The third option was foam blocks, which would have been more expensive than TDA.
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