Add another record to the books of Pennsylvania. The commonwealth is now home to the longest mechanically stabilized earth (MSE) wall in the United States and the second-longest MSE wall in the world, at least according to Sherif Aziz, regional manager for Reinforced Earth Co., Vienna, Va.
Started in February 2004, it's a major portion of the final phase of a $134-million project to eliminate the two-lane bottleneck on Routes 22/322 at the Lewistown Narrows. It adds two more lanes along a stretch sandwiched by Shade Mountain and the Juniata River.
According to PennDOT, the old two-lane highway was a bottleneck, one of only two two-lane sections on the 100-mile corridor between the Hershey/Harrisburg and State College areas. The old, two-lane roadway had a significant crash history, with the Narrows once cited as one of the more dangerous roadways in the nation. Between 1980 and 2000, 20 people died along this stretch.
For many years, engineers studied the Narrows for a reasonable solution to its special challenges. The final design elevated about three miles of the westbound lanes above the eastbound (a bifurcated roadway) to minimize excavation along the talus slope. It included more than four miles of retaining walls, including a two-mile-long MSE wall, and more than 43 miles of remediation pipe piles.
There was extensive geotechnical work before and during design, including more than 40,000 linear feet of core drillings as well as seismic and ground penetrating radar investigation. Stability monitoring of the slope continued even during construction.
Due to tricky site conditions, such as the talus rock formation and underlying layer of slippery clay, plus limited corridor space, the project team was unable to dig into the mountain. They instead elevated the westbound lanes up to 30 feet above grade.
The project consists of 6.65 miles of limited access, bifurcated, both horizontally and vertically, plain cement concrete highway consisting of two 12-foot lanes eastbound and westbound with 10-foot concrete shoulders on the outside and variable, from 4-foot to 9-foot concrete shoulders on the inside.
The roadway construction progresses from a large fill condition in the western sections to a large cut in the eastern sections. The most significant portion of the project has been the MSE walls totaling 14,820 feet in length and the required slope-stability remediation, consisting of approximately 230,000 linear feet of 7-inch-diameter micropile.
At $104 million, this was the second-largest construction project ever bid by PennDOT. The Pittsburgh office of Walsh Construction acted as general contractor on the project. The project team also consisted of PennDOT; Construction Manager Maguire Group Inc., Pittsburgh; Principal Designer EADS Group, Inc., Altoona; and Design Consultants Erdman Anthony Associates, Inc. and GTS Technologies Inc.
When complete in late 2008, there will be a modern, four-lane highway between Milroy, east of State College, and Hershey/Harrisburg.
"This is one of the most complicated and challenging engineering projects that PennDOT and its partners have ever tackled," said PennDOT's District 2 Engineer George M. Khoury III.