AEG Outstanding Environmental & Engineering Geologic Project Award: Route 30 Landslide Remediation

Project Team

Pennsylvania Department of Transportation

Gannett Fleming, Inc.

Golden Triangle Construction Co., Inc.

National Significance of Project

US Route 30 is a major east–west, coast-to-coast highway. The roadway is the third longest US highway, extending 3,073 miles across the northern tier of the US from Atlantic City, New Jersey, to Astoria, Oregon. The portion of Route 30 running through Pennsylvania is perhaps the most famous of all the US highways, the Lincoln Highway, known as one of the earliest transcontinental highway routes for automobiles across the US Today, the route still connects the Commonwealth’s two largest cities—Philadelphia in the east and Pittsburgh in the west.

On April 6, 2018, on a four-lane stretch of the Lincoln Highway located in East Pittsburgh Borough, Allegheny County, engineers from the Pennsylvania Department of Transportation (PennDOT) and Gannett Fleming were investigating a troubled section of Route 30. The roadway, a principal artery between the suburbs and downtown Pittsburgh, was experiencing surface displacement problems.

The investigation revealed much more than expected. The team detected a crack in a retaining wall near the base of the slope below the highway, as well as signs that the retaining wall was beginning to shift— evidence that accelerating surface movements identified at the roadway grade, may be the result of underlying slope movement. Recognizing imminent danger, the team alerted police to evacuate a residential community at the base of the slope.

Within hours and shortly before daybreak on April 7, a landslide sent 300 feet of roadway and thousands of tons of soil plummeting 90 feet down the steep hillside, destroying a home and two apartment buildings.

Project Description

The team’s decisive action to protect the public and remove residents from harm’s way likely saved dozens of lives. Police evacuated more than 30 residents from six apartment buildings. Fortunately, no injuries occurred due to this catastrophic failure. However, the closure of this major highway threatened to paralyze the region.

To restore the key artery and return displaced residents to their homes as quickly as possible, PennDOT partnered with Gannet Fleming and their on-call geotechnical maintenance contractor, Allison Park Contractors (APC), to perform investigation and design concurrently with emergency cleanup operations. Working around the clock, Gannett Fleming delivered a comprehensive landslide remediation design and bid package in just ten days—when the industry norm is ten weeks or more, even under emergency conditions.  During this time, APC also performed dusk to dawn demolition of damaged structures and careful excavation of landslide debris. This extraordinary effort kicked off final construction operations that continued 7 days a week, 24 hours a day, with no holiday breaks, allowing the highway to reopen in less than three months, instead of a more typical design and construction duration of two years.

Environmental and Engineering Geologic Principles Applied

The engineers used an unconventional, aggressive approach to design a 400-foot-long retaining wall and 90-foot embankment, working together with PennDOT and emergency excavators as they began removing approximately 35,000 cubic yards of debris from the site. Although excavation began almost immediately, the team could not wait until debris was removed to begin geotechnical investigations and analyses; or until analysis was complete to begin wall design—standard procedure on most projects. By analyzing data and developing the design simultaneously, the team demonstrated an innovative application of existing techniques to achieve a successful solution in an exceptionally short period of time.

At the team’s direction, excavators removed debris from specific areas to enable drill rigs to access nine core sample borings along the anticipated wall alignment. Geotechnical engineers analyzed samples on the spot to determine how actual conditions aligned with the estimates. Data was conveyed instantly from the field to designers, who refined the design models as needed.

To hit the two-week deadline, engineers gathered as much data on subsurface conditions as quickly as possible, even though layers of rubble still covered the site. They also began wall design immediately, using the data on hand, and continually adjusted the design as new data became available. The unique approach enabled rapid progress.

Available lidar imagery provided site mapping and surface contours and cross sections were cut through the landscape to identify the ground surface prior to the landslide. Mapping was supplemented by 3D aerial photogrammetry using a drone launched within days of the slope failure. With this information in hand, the team created a framework for remediation design options to present to PennDOT. The details of the retaining wall size, type, and location were then confirmed or adjusted as new information became available.

To minimize the environmental impact to the small urban community of East Pittsburgh, the team designed a durable rock embankment supported by an anchored wall. This remedial option was provided to keep the footprint of the reconstructed embankment as small as possible.

Benefit to the Public

Fifty-four contractors and vendors attended the pre-bid for the project, and after 13 days from the original slide, bids were officially opened. Golden Triangle Construction (GTC) was the low bidder at $6.5 million. GTC used a proactive approach to complete construction within the tight timeline. Based on preliminary contacts made by Gannett Fleming, the contractor found a supplier that had in stock the 51 steel beams required for the retaining wall. They understood the importance of the project, so they took a gamble and locked up the steel prior to getting the bid.

GTC immediately stepped into action, relieving PennDOT’s on-call emergency contractor, they continued the landslide debris removal and excavation operations. Working with their previously assembled team of subcontractors and vendors, GTC also began drilled shaft work within 23 days of the bid date. This team was remarkable in the fact that the galvanized soldier piles were delivered and installed in conjunction with the shaft work. The tie-back anchor activities occurred 12 days after the drilled shaft start date, which is further testament to great organization, scheduling, and teamwork. During those activities, 30,000 cy of PTM 510 rock and 14,000 cy of foreign borrow were delivered to the site and placed as the drilled shaft concrete cured. The road reconstruction and drainage were the last activities to occur, and by June 27, 2018, all physical work required to open US Route 30 was complete.

PennDOT Right-of-Way staff, along with Allegheny County Emergency Services and disaster relief organizations, were working behind the scenes during this timeframe assisting the 31 evacuated

residents. They worked day and night to ensure the displaced residents were provided with housing and essential needs. All apartment residents were displaced until construction was completed, and 11 of those residents’ apartments or homes were destroyed.

The remediation of the US Route 30 landslide and the attendance to the displaced residents were the epitome of the ultimate partnering and cooperative experience. Although not without challenges, the urgency and importance of the project was understood by all, and this project was completed three days ahead of an extremely aggressive schedule, and without injury. This could not have been achieved without the collaborative partnership between the designer, the multiple contractors, and vendors involved on the project, PennDOT, and the Federal Highway Administration.

“I want to thank PennDOT’s crew for their countless hours and tireless efforts to get this project done quickly and safely. I am proud of the work we’ve all done together.”
– Tom Wolf, Governor of Pennsylvania

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