Putting a sanitary sewer and water main network under a street in an area of town fraught with excessive moisture and sloping terrain was the challenge for the city of Waconia, MN. The solution came in using Tire Derived Aggregate (TDA) as a lightweight fill.

The project is in a basin. Soil boring tests showed fill, swamp deposits and very loose clay-like sand extending as far as 21-½ feet below the surface. The geotechnical recommendations called for a lightweight aggregate backfill to reduce loading on the utility pipes that were designed to float within the fill embankment.

TDA was selected based on its track record of working in soils that aren’t stable enough to support a project. TDA also reduces loading and pressure against adjoining structures, like retaining walls or pipes. It's also approximately one-third to one-half the weight of soils, free draining and has high shear strength.

Approximately 650 cubic yards of TDA were installed around the pipes. The material will improve sub-base drainage and bring stability to an area that would otherwise not be able to host an underground utility network without concern of damaging the pipes. The light weight of the TDA will reduce vertical and horizontal pressures, and the thermal insulating properties will help prevent pipes from freezing.

The second challenge on the project was to construct a stable road on top of the trench. This is where TDA really shines, according to Monte Niemi, CEO of First State Tire Recycling. "More than 100 roads in Minnesota have successfully been built on top of TDA,“ Niemi said. “The dual responsibilities in the Waconia project showcase the unique, cost-effective benefits of R.-T.E.A.”

When asked why R-T.E.A. was chosen for this project, Bolton and Menk engineer Jake Saulsbury said, “Tire-derived aggregate is lower costing than other aggregate products, is more durable, and easier to install than Styrofoam.” Saulsbury said that Bolton & Menk will be using TDA again in future projects.