River Road in Bismarck, North Dakota needed a solution for a slope issue. The road had settled 2-3 feet and was closed for four months. The slope that was failing is along the Missouri River, meaning the project was not able to excavate too deep without impacting the river-way. The plans to stabilize the slope included a combination of driven piles and TDA (tire-derived aggregate), which is a lightweight fill.

Slope failures generally occur from a lack of shear strength. In engineering, shear strength is the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. (A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force.)

In this scenario, underlying soil movement caused a slide and the resulting surface failure. There was not enough shear strength to restrain the soil movement or prevent it from affecting the surface. Reducing the weight of the failure location was perhaps the most important part of the repair project. Soil weighs approximately 2,200 lbs. per cubic yard, and that number can increase significantly depending on moisture content. TDA, on the other hand, weighs 600 lbs. per cubic yard dry or wet.

The combination of being a lightweight fill, having permeability, and possessing high shear strength makes TDA a great material for slope stabilization projects such as this.