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County engineer details multi-year slope-stabilization work on major roadway failure
Summary
Jackson County’s engineer and public-works staff presented the cause, investigation and a county-led repair of a large slope failure affecting a switchback section of a county road, describing soil borings, mass-wave studies, soil nails, shotcrete walls, micropiles and wick drains used to stabilize the slope.
County engineers and public-works staff presented a detailed briefing on a major slope failure and the county-led stabilization work completed on the site, summarizing geotechnical investigation, design elements and construction progress.
County Engineer Jonathan (last name not provided) walked commissioners through photographic evidence of a multi-year failure and described subsurface investigations, including borings and mass-wave (MASW) geophysical testing. He said the MASW and borehole data showed soil stratification and anomalies that required subsurface stabilization, and that water infiltration was a principal driver of the recurring failures.
The repair employed engineered slope-stabilization methods: soil nails installed in multiple rows, shotcrete facing, horizontal and vertical drains (wick drains) behind the wall to reduce pore-water pressures, and a reinforced concrete cap tied to micropiles. The engineer emphasized the need for a system that controls water—intercepting and redirecting upslope drainage—and for a reinforced face to hold the slope. Photos and on-site descriptions show the county performed much of the clearing, excavation and hauling using county crews; the presenting engineer thanked a cooperating private landowner for granting construction easements and permission to remove timber.
Construction sequencing followed a top-down approach with benching, sequential nailing and grouting, shotcrete placement and installation of drains and a cap. In the lower section crews encountered a seasonal groundwater surge during excavation; staff described that discovery as consistent with the hydrologic conditions contributing to the failure. The engineer said roughly 5,200 cubic yards of material were moved (approximately 315 truck loads) and that crews installed multiple stabilization lifts and drainage features to manage long-term stability.
Commissioners praised county crews for the scope of the work. District 4 Commissioner McBride said the project demonstrated significant county capability and engineering; several commissioners urged continued monitoring and documentation.
Ending: The briefing closed with staff saying the stabilization work is largely complete and that long-term monitoring and maintenance will be required to ensure slope stability, especially given the site’s subsurface water conditions.
