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by Jim
Schill
NUCA
contractor D’Allesandro Corp., Avon, MA, recently completed a
large-diameter storm sewer replacement project for Boston
Water and Sewer Commission (BWSC), Boston MA. The Stony
Brook Sewer Separation project was part of a major storm
sewer, sanitary sewer and water main replacement and rehabilitation
program aimed at mitigating I&I and eliminating combined
sewer overflows (CSOs).
According to D’Allesandro Senior Project Manager John
Bauld, the project was originally specified as open cut,
but was well suited for pneumatic pipe bursting. He said,
"The location of the project and surrounding structures
really made pipe bursting an ideal choice for the project.
After we were contracted for the work, we suggested a pipe
bursting option and it was accepted."
For the replacement of the existing 12-inch VCP storm sewer
with 20-inch HDPE, Bauld chose a 14-inch pneumatic Grundocrack
Koloss from Associate NUCA member TT Technologies, Aurora,
Ill.
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The
D’Allesandro crew used a 14-inch diameter, reversible
Grundocrack Koloss to replace 53 feet of 12-inch
VCP storm sewer with 20-inch HDPE.
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Project Background
The
BWSC, along with the Massachusetts Water Resources
Authority (MWRA) have been targeting issues like I&I
and CSOs since the mid-1980s. The BWSC recently implemented
several projects under its CSO plan. The scope of the
projects ranges from new water main installation to
the replacement of aging storm and sewer drains. Other
portions like the Stony Brook project, are aimed at
separating combined sanitary and storm sewer systems
in order to reduce pollution levels in natural waterways
such as the Stony Brook Conduit, the Muddy River and
the Charles River.
Bauld said, "The objective of separating sanitary and
storm sewers is very basic. Removing storm water from sanitary
sewer lines reduces the amount of water being treated at
the treatment facilities. It’s water that doesn’t
need to be treated anyway. Separating the lines also effectively
eliminates combined sewer overflows. This keeps the sewage
from backing up into homes and overflowing into rivers,
streams and bays."
Pipe Bursting
With several
thousand feet of bursting experience in projects ranging
from 4 inches through 20 inches in diameter, Bauld
and the entire crew were able to see that replacing
this particular storm sewer section would be best accomplished
through the trenchless method.
He said, "The main reason we decided to use bursting
was the existing pipe ran under a field-stone wall that’s
probably close to 200 years old. The wall stands eight
feet high and four feet wide and surrounds the Arnold Arboretum,
which is maintained by Harvard University. In addition
to the wall, arboretum officials were concerned an open
cut project would disturb several large and rare trees."
Bauld contacted TT Technologies pipe bursting specialist
Ric Micellota for technical support. Micellota said, "After
reviewing the project with John, we decided to use a pneumatic
straight barrel reversible tool. That way, we only needed
to dig a launch pit and could burst from the launch pit
to a manhole and then reverse the tool out through the
new pipe. This would create the least amount of disruption.
We also opted for a larger bursting tool because of the
substantial upsize. Twelve inches to twenty inches is significant."
On The Job
Bursting
was scheduled for a Wednesday however, a poor weather forecast
prompted Bauld to push the timeframe forward 24 hours and
attempt to burst on Tuesday instead. He said, "I called
Ric at TT Technologies at 7:00 am and told him we wanted
to burst that day. He arrived at the job site several hours
later and we were ready to go."
While the 14-inch diameter Koloss was fitted with a 23-inch
OD front expander to allow the upsize from 12-inch to 20-inch
pipe, the D’Allesandro crew prepared the launch pit.
Bauld said, "The launch pit was located at the base
of a small rise. At that point, the pipe was only 5 feet
deep. This allowed us to use of a relatively small launch
pit. The run was approximately 53 feet. I had the pipe
fused at the factory and delivered to the site in one piece."
Bursting proceeded without complications. The 53 feet of
12-inch VCP storm sewer was upsized to 20-inch HDPE in
approximately 20 minutes. Once installed, the D’Allesandro crew put
the tool in reverse and backed out to the launch pit through
the new HDPE. The tool’s front expander was then cut
from the front of the pipe and removed through the manhole.
Everyone associated with project was pleased with the results.
Bauld said, "Prep worked started around 11:00. We
started bursting at 2:00 by 2:20 we were done. It went
like clockwork!"
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