Total
Rehab
Replacing a failed sewer system is a
big job and expense for any municipality. This was especially
true for the some four hundred citizens of Mansfield, WA, as they
were faced with replacing their entire sewer system.
 Installed
in 1952, the old concrete pipe sewer was now crumbling beneath
them. "We had some unreal flows and knew we had an infiltration
problem," said Mansfield City Superintendent John Cavadini.
Cavadini, along with other city officials,
then consulted with the engineering firm of Hammond, Collier
" Wade-Livingston Associates Inc., of Chelan, WA, to identify
the source of the problem and find feasible solutions.
The town had previously worked with Hammond, Collier " Wade-Livingstone
when they needed a new municipal water system in 1990.
To get a better idea of the degree
of deterioration, the engineering firm brought in a specialist
to "TV" the lines. Although the video service didn't have
a camera for the six-inch lines, the eight- and ten-inch sewers
showed considerable decay and tree root infiltration.
This information was key to obtaining federal moneys for a new
system.
Because of the incredible impact
that this project would place on this tiny farm community, the
engineering firm recommended allowing alternative forms of renovation
(other than trench and replace) to be allowed when it went to
statewide bidding. Hammond, Collier " Wade-Livingstone
had previously recommended pipe bursting in a similar situation,
with a positive outcome. Base don the engineering firms
estimate, funding was secured from the Community Development
Block Grant Program and the USDA in the form of a grant and
low interest loan.
Pipe
Bursting Selected
Bid requests were let to replace 13,000
feet of the most critical lines, which constituted approximately
70 percent of the town's sewer lines. Seven firms responded,
one of which incorporated the alternative method of pneumatic
pipe bursting as part of their estimate. The contractors
was Pape " Sons, headquartered in Seattle, WA. Their
bid was ultimately accepted for several reasons.
"One of the reasons we chose [the}
pipe bursting [bid] was because of all the restoration problems
involved in tearing-up streets in open cut," cited Cavadini.
As stated earlier, the city had gone through the surgery of
open cut for the installation of water lines several years ago,
and Cavadini expressed, "We didn't want to go through that again.
The other main reason for the pneumatic
pipe bursting bid to be awarded was due to economics.
It came in at $210,000 less than the average open-cut bud.
Don Phelps, Branch Manager of Hammond, Collier " Wade-Livingstone,
said, "You can expect 10 to 20 percent savings with pipe bursting
over open cut." Phelps indicated that the typical open
cut jobs costs about $50-55 per foot, whereas bursting comes
in around $40 per foot.
 This considerable savings allowed
the community to let a second contract and change order for
an additional 5,000 feet of sewer line (for a total of 18,000
feet). This additional footage included the line running
out of town to the wastewater treatment lagoon. Once again,
Pape " Sons secured the low bid by incorporating pipe bursting.
The
Contractor
Two years ago, Dick Harrod of Pape
" Sons had started looking for economical alternatives to
the standard open cut scenario because of the increasingly leaner
and meaner bidding processes. In his quest, he became
familiar with the trenchless technology of pipe bursting through
several sources. After careful review and observation,
Harrod was convinced. Based on his recommendations, Pape
" Sons made an initial investment in this new technology
several years ago. Now, Harrod is considered a veteran,
having supervised several bursting jobs in the Pacific Northwest,
including a recent one at McChord Air Force Base in Tacoma,
WA.
Harrod arrived in Mansfield in mid-August
with two crews of men and two pneumatic bursting tools.
The two tools were a Grundocrack PCZ-180 for bursting the smaller
diameter pipe, and a Grundocrack Hercules for the larger.
The tools were selected based on their pneumatic power and,
most importantly, their diameters and suitable available expanders.
Both tools were obtained through TT Technologies, a manufacturer
of trenchless tools and accessories in Aurora, IL.
The soil conditions in Mansfield
are not conducive to digging or trenching. The dense and
rocky ground consistency is a result of ancient volcanic activity.
But, since the pipe bursting tools would be following pre-established
routes, the difficult soil was not a factor.
Job
Specifics
The total of 18,009 feet of bursting
broke down into three categories: 4,756 feet of 10-inch
concrete was replaced with 10-inch HDPE pipe; 10,128 feet of
eight-inch concrete was converted to eight-inch HDPE pipe; and
3,123 feet of six-inch concrete was upgraded to eight-inch HDPE
pipe. The high density polyethylene pipe was selected
for its unique flexural qualities that allows great lengths
of pipe to be simultaneously pulled into ground as the tool
bursts the failed line. HDPE also has an indefinite service
life, meaning it will probably never need to be replaced.
The HDPE pipe for the Mansfield job was specified as SDR 21
with the interior of the pipe having "a light reflective color
to allow easier/better viewing for television inspection."
All HDPE pipe was provided by Maskel-Robbins of Seattle, WA.
Harrod utilized two crews, each of
which was equipped with one of the Grundocrack tools, depending
on the run's characteristics. Runs averaged 350 feet,
with some as long as 500 feet. Typically, the runs were
from manhole to manhole with several lateral service connections
made along the line. An entry pit would be prepared to
access the failed pipe and receive a winch line, which would
be fished back from the tool exit area several hundred feet
away. The tool, with appropriate expander for the burst,
would then be attached to the winch line, and launched from
the entry pit.
Developed to complement the bursting
tools, Harrod incorporated two Grundowinch trailer mounted winches.
The Grundowinch is a self-contained unit that can be easily
positioned above a manhole or opening. An extension boom
adjusts for pipe bursting in a variety of pipe depths.
The combined effect of the percussive
pneumatic power of the tool, coupled with constant tension supplied
by a hydraulic winch, propelled the tool and new pipe through
the old line. Once the line was in, lateral connections
were made.
Reflecting back on the job, Harrod
stated that he would approach the job differently if he were
to do it again. "I'd still use two crews, with one performing
a burst and the second attending to the manholes and laterals."
Most of the runs were away from main
thoroughfares, following alley ways. "The pipe bursting
process works especially well in tight areas," stated Eric Smith,
who was the engineer for Hammond, Collier " Wade-Livingstone.
Importance
of Expanders
Expanders played a key role in the Mansfield job, as they do
in most every burst. Primarily, an expander pushes old
pipe fragments and soil out of the way for the safe installation
of the new pipe. In instances where a larger diameter
pipe is desired (as opposed to what is currently in the ground),
the expander produces a wider bore to accommodate the installation
of the larger pipe. This was the situation when crews
were replacing six-inch concrete pipe with eight-inch HDPE.
Crews used a Grundocrack PCZ-180
(with a seven-inch diameter), fitted with a 10-inch rear expander
to provide ample room for new eight-inch pipe. The tools
air consumption is 175 cfm and operates at 100 psi. The
rear expander attached to the back of the tool, with the HDPE
pipe threaded inside of it.
The larger Hercules tool has a diameter
of 8 1/2-inches with an air consumption of 280 cfm. To
burst the 10-inch concrete pipe, the Hercules was fitted with
a full (12-inch diameter) body expander. The full body
expander is like the housing of a ball-point pen, allowing only
the front tip of the bursting tool to be exposed for attachment
to the winch line.
Pipe bursting accessories important
for the success at the Mansfield site included an in-line lubricator,
which provided adjustable lubrication to the tool. This
lubrication was dispensed through the air line to the inside
of the tool to reduce friction between the single piston and
cylinder. Another important accessory was the shock valve.
This device allows the proper amount of pneumatic pressure to
build-up in the air line before the tool is engaged in the burst.
This meant that only full power was supplied to the tool, guaranteeing
now weak starts. This is especially beneficial when long
air lines are required.
Job
Completed
By the end of November, the last of the 53 runs were completed.
The project wasn't intended to last three and one-half months,
but the crews got off to a slow start. "It started very
slow. We had difficulties with support equipment breaking
down, as well as illness with some of the crew," said Harrod.
Further slowdowns resulted from locating
each lateral connection. The infiltration into the old
pipe had disguised some laterals from the video camera.
And, as stated earlier, the six-inch pipe was not televised,
so crews had to guess as to where each lateral might be located
on those lines. In all, there were 166 lateral connections
made.
The crews also replaced or restored
57 manholes throughout the community.
With the arrival of winter, it was
decided that final rehabilitation work will need to wait until
spring to be completed. The good news for Mansfield is
that all sewer services are up and operational. Not only
that, but they got a lot more new sewer for their money.
Commenting on the scope or the job, TT Technologies Pipe Cracking
Product Specialist Mike Schwager said, "It is one of the single
largest sewer rehabilitation projects to use pipe bursting in
North America."
"All in all, it was definitely a
positive situation," according to Phelps. Cavadini agreed,
stating "I'd say it went real well. The pipe is in the
ground.
" Pipeline " Utilities Construction,
February 1996, Pages 49-51
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