The stability of a talus slope along a section of an existing highway was investigated. This highway section was on routes US 22 and 322 located at the Lewistown Narrows in the state of Pennsylvania. For the investigation, subsurface explorations involving borings, seismic refraction survey, and very low frequency (VLF) radio wave measurements were conducted. Also, piezometers and inclinometers were installed to monitor groundwater level and creep, respectively. The talus slope was analyzed on a PC using Bishop's Simplified Method of analysis for both probable maximum flood and 100-year flood conditions. Results of the analysis indicated that the slope was stable even under the 100-year flood condition. However, there were concerns over water ponding and creep effects on the talus slope stability. Various remedial measures were proposed to enhance the stability of the slope.


In the state of Pennsylvania, USA, routes US 22 and 322 are major highways leading to the state capital. Near the capital, these two routes merge and carry heavy traffic. A portion of the merged and heavily trafficked highway is located between the Juniata River on the south and a steep slope of Shade Mountain on the north, in what is known as the Lewistown Narrows. As the name implies, the Juniata River Valley in this section is very narrow, being confined by the steep slopes of Shade Mountain on the north and Blue Mountain on the south. The Shade Mountain slope is very steep and the lower portion of the slope is generally covered with talus. Because this section of highway (approximately 9.5 km long) has only two lanes, one in each direction, a four-lane, limited access, bifurcated roadway on the talus slope is planned to accommodate the heavy traffic and improve safety within this restricted area.

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