This stretch of highway in central Pennsylvania has long been considered one of the most dangerous highways in the United States, with the dubious distinction of making Readers Digests list of top 10 most dangerous highways. The goal of the project was to construct a four-lane highway over the narrow strip that currently carries the existing two-lane highway. The narrow strip is bounded by the Juniata River and an old Pennsylvania Canal to the south and by very steep boulder fields and unstable colluvial soil slopes to the north. This challenge has delayed the project for over three decades, as engineers could not produce a suitable design to ensure roadway stability. GTS mobilized and managed 11 geotechnical engineers who completed the final design within 9 months. This administrative obstacle was complicated by the challenge of coordinating the 10 review agencies involved with the project.

The geotechnical challenge was complicated by the complex geology of unstable colluvial and talus slopes overlying a residual clay shear plane, along which sliding of the entire roadway embankment would occur. To understand the conditions, GTS performed over 800 core borings along the entire alignment. Geophysical investigations, consisting of very low frequency surveys, seismic refraction profiles, ground-penetrating radar, and vibration analyses, were also used to supplement the boring program.

To assess the stability of the roadway GTS performed two-dimensional slope stability analyses considering 56 possible modes of failure at approximately 90 stations along the alignment. Numerous potential remedial solutions, including construction of embankment with lightweight fill, utilizing tiebacks to resist failure, construction of a secant drilled shaft wall, and utilizing "beefed up" retaining wall structures, were developed by GTS for consideration.

The final solution to resist failure of the highway was a system of discrete micro piles socketed into bedrock, acting as shear pins. These piles were designed to provide up to 60 tons of resistance per foot of roadway. The entire project included over 220,000 linear feet of micro piles, oriented on 1 to 6 foot centers, to maintain stability of the roadway and structures.

The project also included the design of six bridges, nine cantilever retaining walls totaling over 8,500 feet in length, four MSE retaining walls totaling over 15,000 feet in length, and four culverts. Roadway issues included the design and installation of 344 rock anchors to stabilize a rock cut with unfavorable bedrock dip, design of rock cuts 145 feet in height, design of steepened embankment slopes supported by a rock buttress overlying the canal, remediation of rock fall hazards via fencing, grouting, bolting and nets, design of 11,500 feet of temporary geosynthetic reinforced soil slopes, and the stability monitoring of the construction with 28 piezometers, 35 inclinometers, and 8 strain gauges. GTS will provide support during construction by monitoring and interpreting the instrumentation data, to ensure that the stability piles are functioning as designed.