US 421 SLOPE STABILIZATION ON PINE MOUNTAIN USING A TIEBACK WALL-PPT Presentation

PPT Presentation

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The presentation describes stabilization of a failed slope along US 421 on Pine Mountain, about eight miles north of Harlan, Kentucky. A February 2019 storm triggered the slide, and the site’s narrow, curving two-lane highway was at risk from continued movement. KYTC and FHWA approved a permanent rock-anchored tieback wall for Emergency Relief funding.<br /><br />Investigations included soil and rock borings, rock-line soundings, slope inclinometers, and groundwater wells. The slope consists of clayey colluvium with rock fragments over Grainger and Chattanooga shale. Groundwater was generally 7–8 feet deep, and monitoring recorded movements of roughly 2–4 inches. Back-analysis indicated an existing factor of safety of 1.0.<br /><br />The stabilization design used soldier piles embedded at least 18 feet into bedrock, with a tieback wall and facing. Two-dimensional limit-equilibrium analyses set wall loads to achieve factors of safety of 1.3–1.4. At the most demanding section, the wall was 46 feet high and designed for 84.6 kips of earth load per linear foot. Anchors were inclined at 20 degrees; each comprised two 12-strand tendons with a 50-foot bond length and a factored design load of 395 kips.<br /><br />The project used conventional design-bid-build procurement, while the specialty contractor completed detailed wall and anchor design, construction, and anchor testing under performance-based specifications. The total contract bid was approximately $5.86 million.

Keywords

slope stabilization

US 421

Pine Mountain

Harlan Kentucky

rock-anchored tieback wall

emergency relief funding

soldier piles

groundwater monitoring

limit-equilibrium analysis

anchor testing