FEATURE ARTICLE Micropiles in the Smoky Mountains Foothills DFI COMMITTEE PROJECT FUND Beginning in the late 1930s, increased travel in the vicinity of the Great Smoky Mountains National Park in Gatlinburg, Tenn., created traffic congestion as the existing road system was ill-equipped to handle the recreational traffic associated with the recently established national park. Then vice president of the Great Smoky Mountains Conservation Association, Frank Maloney, proposed the construction of a scenic parkway along the foothills of the Smoky Mountains. The three main purposes of this parkway would be: (1) to provide panoramic views of the Great Smoky Mountains National Park, (2) provide access to several areas within the park, and (3) help alleviate congestion on the existing road system. The Foothills Parkway was subse- quently authorized by an act of Congress in 1944. The following year the Ten- nessee Legislature appointed the Tennessee Highway Department to purchase the right-of-way for the parkway. In 1947, the right-of-way was AUTHORS transferred to the National Park Service. Construction of the parkway began in 1960 and is yet unfinished. A section of the parkway extending from Walland to Wear Valley, Tenn., is complete with the exception of a 1.6 mile (2.6 km) segment known as the “missing link.” In the 1980s, an attempt was made to build an at- grade road along the missing link, but steep slopes and unstable ground quickly stopped construction. A geotechnical study that involved access using helicopters was performed in the 1990s. On the basis of the results of the test borings, it was determined that marginally stable colluvium was present in an area that would later be designated as the site for Bridge No. 2. In 2009, the Eastern Federal Lands Division of the U.S. Department of Transportation and the National Park Service solicited design-build proposals for Bridge No. 2 spanning the colluvium. The design-build proposals were judged based on a number of considerations including disturbance to the site. The team, led by Aerial photograph of project site Bell Construction, Inc. (Nashville, Tenn.), was selected. Other team members included VSL LLC (Denver, Colo.), Corven Engineering, Inc. (Tallahassee, Fla.), the former Structural Preservation Systems (Hanover, Md.), and Palmer Engineering (Nashville, Tenn.). The project was part of the American Recovery and Reinvestment Act of 2009, and served as a stimulus project for Tennessee. Bridge No. 2 is a 5 span bridge with a total length of 790 ft (240.8 m) and a maximum pier height of 50 ft (15.2 m). Following construction, it joined a series of bridges along the Foothills Parkway that are not connected or open to the public yet. Micropile Design and Instrumentation Given the emphasis on minimal site disturbance, the design-build team elected to use micropiles for support of the temporary trestle and the planned pre-cast segmental bridge. The design was performed according to the AASHTO LRFD Devin T. Dixon, FHWA; Ronaldo Luna, P.E., Ph.D., Missouri University of Science and Technology; Kyle Kershaw, P.E., Ph.D., Rose Hulman Institute of Technology; and Timothy C. Siegel, P.E., G.E., D.GE, Dan Brown and Associates, PC DEEP FOUNDATIONS • JULY/AUG 2014 • 61
