Slope Repairs in a Tight Footprint: Slope Stabilization using Multiple Technologies-Paper

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In June 2009, more than five inches of rain fell in 36 hours, triggering a landslide that displaced up to three feet of a 300-foot section of River Road in Bismarck, North Dakota. The road was closed. The failure extended toward the Missouri River, where most of the slope was under U.S. Army Corps of Engineers jurisdiction. Permitting work on the river-facing slope could take over a year, while the city needed to reopen the road quickly and preserve the scenic landscape.<br /><br />Investigations found that the failure surface lay mainly in saturated, variable soils overlying weathered bedrock. Monitoring and analysis indicated that rainfall-related seepage had contributed to movement. Because repairs had to remain within the roadway right-of-way, the team selected a combined approach: two rows of driven steel H-piles, battered into sandstone bedrock to resist slope movement, and a lightweight fill section beneath the rebuilt roadway. Shredded tires were used as fill to restore the road grade while limiting additional load on the unstable slope.<br /><br />Construction began in October 2009, and the road reopened in November, about five months after the failure. Monitoring recorded limited movement during and after construction, followed by negligible movement through 2011. The repair remained stable during major flooding that year, and later site visits found no visible distress. The project demonstrated how combining deep foundations with lightweight fill could provide an expedient stabilization solution while avoiding work in the regulated river corridor.

Keywords

landslide

River Road

Bismarck North Dakota

Missouri River

H-piles

slope stabilization

lightweight fill

shredded tires

road repair

rainfall seepage