UT.NP.ARCH.100(2).Bridges on Delicate Arch Road.Geotech Rpt FINAL.February 2025.pdf

This is a Geotechnical Report prepared for the Bridges on Delicate Arch Road project (UT NP ARCH 100(2)) within Arches National Park. The report provides subsurface investigation and soil analysis necessary to support the design and construction of three 100-foot span concrete bridges crossing ephemeral washes (Salt Valley Wash, Salt Wash, and Winter Camp Wash) along Delicate Arch Road.

The geotechnical investigation addresses subsurface conditions at each bridge crossing location to inform foundation design, embankment construction, and roadway reconstruction efforts. The existing culverts installed during the mid-1990s are inadequate for unobstructed stream flow and sediment transport, resulting in flooding, sediment deposition, road closures, visitor safety concerns, and high operational costs. The project scope includes reconstruction (4R) work with one segment of restoration (3R), roadway profile elevation to accommodate 10-year design frequency flooding, realignment at Salt Valley Wash with bridge relocation north of existing roadway, and full-depth reclamation or pavement removal with 4-inch overlay on remaining sections. Principal work items include embankment construction (10,000 cubic yards), placed riprap (1,725 cubic yards), roadway aggregate (5,140 tons), and asphalt concrete pavement installation. This Federal Highway Administration project is executed through the Department of Transportation and represents a significant infrastructure improvement to enhance visitor safety, maintain roadway functionality during high visitation periods, and restore proper hydrologic and sediment transport conditions in the Salt Wash Basin.