Engineering Inc. - May/June 2019 - 57

of strength. Making mat"Typically for a job like this, even under
ters worse, the region had
record amounts of rainfall
emergency conditions, three months of design
in 2018.
Gannett Fleming's
would be more in the realm of possibility."
familiarity with the local
BRIAN HEINZL
terrain and its more than
PROJECT
MANAGER
25 years of work with
GANNETT FLEMING
PennDOT would prove
critical on the morning
evacuated from the buildings below. Once the site and surrounding
of April 7 when the retaining wall catastrophically failed. Three
areas were secure, excavation started immediately.
hundred feet of roadway and thousands of tons of soil plummeted
"First, we had to determine how much we could safely excavate,"
90 feet down the steep hillside, destroying two apartment buildings
says Heinzl. "We ascertained the slide was in a confined ravine,
and a single-family home.
so we could move most of the debris and soil without impacting
adjacent properties."
DESIGNING THE NEW WALL
Because it was necessary to clear the site right away, Gannett
Route 30, which winds east-west through the district, is
Fleming engineers could not wait for the approximately 35,000
a critical commuter route for Pittsburgh. On an average day,
cubic yards of debris to be removed before beginning geotechnical
30,000 vehicles would cross the location of the landslide. With
investigations and analysis. Furthermore, they could not wait to
no easy detours, having the road out of commission majorly
complete the analysis before designing the new retaining wall.
inconvenienced the entire region.
Heinzl and his team used available LiDAR imaging to determine
Gov. Tom Wolf toured the site soon after the slide and emphathe surface contours of the site and utilized a drone to provide 3D
sized the need to open the road as soon as possible. At the time of
aerial photogrammetry. The preliminary design and location of the
the governor's visit, Gannett Fleming engineers were already well
new wall were based on this information.
into the initial phase of project design.
At the direction of the engineer, excavators removed debris from
Immediately following the landslide, PennDOT, Gannett
specific areas in order to allow drill rigs to access critical core sample
Fleming and other contractors were on-site to ensure the slope
borings along the anticipated alignment of the wall.
was not going to move any farther and that everyone had been
"We had to make educated design assumptions that turned out

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Engineering Inc. - May/June 2019

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