Abstract:
The Kentucky Transportation Cabinet (KYTC) is administering a $6 million construction contract that includes a permanent tieback retaining wall to stabilize an earth slope on US 421 near the base of Pine Mountain in southeastern Kentucky. The KYTC Geotechnical Branch completed the subsurface exploration, tested soil and bedrock samples, monitored slope displacements and groundwater levels, and performed engineering analyses.
Contract documents included geotechnical data, wall geometry, design loads, and performance-based specifications that require a qualified specialty contractor to design and construct the 650 ft. long wall. It has a maximum design height of about 50 ft. and factored earth pressures up to approximately 2000 psf. In order to provide resistance along the entire sliding mass, most of which is several feet below the wall facing, the specified design loads consider arching between the soldier piles. The contractor’s design includes grouted permanent rock anchors with up to 12 strands and maximum factored design loads of nearly 400 kips. Drilled soldier piles are designed to be embedded up to 18 ft. into bedrock with maximum socket diameters of 3.5 ft.
Due to the potential for additional slope displacements that could lead to a road closure and require a detour of about 50 miles, the contract includes specified milestone dates. The contract was awarded in August 2021 and requires the contractor to complete 75% of the anchors by January 31, 2022 and finish the wall by May 31, 2022. KYTC and the contractor’s team have worked very closely together so the contractor could procure materials and begin construction simultaneously with completing the design calculations and construction drawings.