Reinforced Earth Company World’s second-largest MSE wall will carry two new lanes of arterial traffic.

Once one of the nation’s most dangerous roads, Route 22/322 in Mifflin County, Pa., is trading notoriety for engineering history with the world’s second-longest mechanically stabilized earth (MSE) wall.

The 10-mile, $135-million widening job, slated for completion in 2008, is one of the state’s most complex ever. It includes thousands of drilled minipiles, and now a 2.5-mile, 240,000-sq-ft MSE wall. The wall supports two new 12-ft-wide lanes in a bifurcated alignment that squeezes through the aptly named “Lewiston Narrows,” between the Juniata River and Shade Mountain.

“To the best of our knowledge, this is the longest and largest MSE wall in the U.S. or Canada, and the second-longest in the world,” says Sherif Aziz, regional manager for Reinforced Earth Co., Vienna, Va., the wall’s designer and supplier. 

The Pennsylvania Dept. of Transportation in two earlier phases had brought the Narrows’ bookend interchanges in Lewiston and Arch Rock up to four-lane standards. But tricky site conditions and limited corridor space made the last 6.65-mile segment tricky. “The talus rock formation and underlying layer of slippery clay prevented us from digging into the mountain,” says Karen Shutty, design manager for The EADS Group, Altoona, Pa., the principal designer.

That left Route 22/322’s widening plan nowhere to go but up. One mile east of the Lewiston interchange, the MSE wall gradually elevates the new westbound lanes to 30 ft above alignment on 400,000 tons of backfill with 41,000 steel reinforcing strips. 

Before work got under way on the wall last spring, the Pittsburgh office of Walsh Construction installed some 9,000 7-in. diameter grout-filled remediation piles (ENR 2/14/05, p. 16) and 8,280 ft of nine concrete shoreline retaining walls. Some 40,000 ft of H-piles were driven for the retaining wall and for two bridges.

The stabilization allowed PennDOT to shift existing lanes, but work space for the wall remained tight. The proximity of active lanes required a temporary reinforced soil slope to provide a platform for foundation work, with gaps every half mile or so as access points, says Walsh project manager Chuck Zugell. More than 4,750 precast concrete panels front the wall, each 5 x 10 ft and 5.6-in. thick. Some 300,000 cu yd of backfill is wedged into the zero- to 20-ft gap separating the MSE backfill from the mountain slopes. The majority of construction work on the wall was completed in July 2006.

Once paving of the westbound lanes is completed, traffic will be shifted so that the existing road can be upgraded into dedicated eastbound lanes. Video monitoring, a highway advisory radio system, weather station, and high-water detectors will enhance safety for motorists, while a new Pennsylvania Canal park with a visitors’ center, interpretive towpath trail and fishing/boating access will complete the project.