Stabilizing Landslides in the Pennington Shale with Drilled Ground Anchors-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the stabilization of landslide-prone slopes along I-40 in Roane County, Tennessee, using drilled ground anchors. The site lies in the variable Pennington Formation, where weathering shale and sandstone creates loose, boulder-rich colluvium. Because this material is more permeable than the underlying strata, water can become trapped and increase slope pressures. Movement along the corridor has persisted since I-40 construction in the 1960s despite drainage measures.<br /><br />After flooding in February 2019 triggered more than 100 landslides statewide, TDOT identified two I-40 locations requiring urgent repairs. The eastbound site was stabilized with a soldier-pile and lagging wall supported by ground anchors. The larger, more complex westbound site required extensive investigation: 35 borings, six slope inclinometers, 22 vibrating-wire piezometers, electrical resistivity surveys, and geological mapping. Modeling identified four significant slides and helped locate suitable anchor-bearing strata.<br /><br />The westbound design used drilled anchors and concrete bearing blocks. A contractor-proposed value engineering change increased anchor capacity and reduced the number of blocks. Before approval, TDOT required load testing; the revised system included 12-strand anchors, 8-inch diameters, and 500-kip test loads. The presentation notes that anchor design relied on thorough site characterization and evaluation of slip surfaces, free lengths, and bearing strata.<br /><br />The project was awarded to Goettle, Inc. in 2020. Construction involved drilling and stressing anchors, load testing, and placing precast concrete blocks. At the time of the presentation, the eastbound work was complete and westbound drilling was approximately 50% complete, with stabilization potentially finishing by January 2023. Ground anchors were presented as a practical restraint option for deep colluvium where conventional removal or stone buttresses would be impractical or costly.

Keywords

landslide stabilization

ground anchors

I-40 Tennessee

Roane County

Pennington Formation

colluvium

soldier-pile wall

drilled anchors

slope remediation

TDOT