bridge,” he said, noting that metamorphic
rock in this region can be
highly variable over short distances.
The site contained primarily Schist,
but production was hampered when
crews hit Amphibolite. This extremely
hard metamorphic rock was prevalent
near the western abutment and the
Crum Creek channel.
Bradfield recalls watching production
drastically improving from
as little as two feet per day with an
auger to a foot an hour using the
BAUER roller bit core barrel, which
is recognized as a respectable rate of
production in hard rock. Walsh initially
tried a cluster drill but had no
luck keeping the tool straight. The
switch to roller bit core barrels also
quieted drilling chatter and reduced
the strain on the drilling rigs.
Walsh purchased 10 tools from
ECA, including primarily 36-inch
augers, core barrels, drilling buckets,
and roller bit core barrels. There were a
few 42-inch tools for overburden areas
where the rock was not immediately
below the surface.
Site access, low overhead, steep
slopes and vibration monitoring
The topography surrounding the viaduct
is complicated by steep inclines,
wetlands, the meandering Crum Creek
and a narrow, snake-like access road,
all encapsulated within a densely
wooded area that happens to be a designated
arboretum. This challenging
terrain dictated not only the selection
of rigs, but also the site preparation.
One of Walsh’s main challenges,
however, was drilling foundations in
hard rock beneath the viaduct with
limited headroom near the east and
west abutments. Watching the BG 18
H drilling below the farthest western
span of the viaduct makes it clear why
its low headroom capabilities were
essential. The rattling tip of the mast is
within mere inches of the steel girders.
The BG 18 H worked in standard configuration
from late June through early
October and was then reconfigured to
low headroom.
Vance says the height restricted
areas were more severe than expected
because the viaduct elevations Walsh
was initially given did not account for
drilling nuances. He indicates that
maneuvers such as putting the drilling
rig in crowd force, or pulling up a full
bucket can require up to eight inches of
additional overhead space.
One of SEPTA’s key concerns
was ensuring that its commuter
trains could continue to pass safely
across the existing viaduct during
PROJECT SPOTLIGHT
A BAUER BG 18 H works in standard configuration as a commuter train travels across
the Crum Creek Viaduct. One of SEPTA’s key concerns was ensuring that its customers
could continue to pass safely across the existing viaduct during construction.
“Drilling
is make
or break.
Depending
on how that
goes, it’s
almost how
the whole
job goes.”
– Richie Vance,
Walsh Construction
CONTINUED ON PAGE 60
58 Q2 2016 www.pilingcanada.ca
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