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by Jim Johnson
In the small community of Darien,
Illinois, the DuPage County Department of Environmental Concerns
(DEC) is in the process of renovating its sanitary sewer system.
The job would prove to be rather diverse, requiring the use
of several old and new methods, including trenchless technology.
 In
1993, the DuPage County DEC retained Engineering Resource Associates,
Inc. (ERA) of Wheaton, Illinois, to evaluate the problem of
I/I in these Chicago-area communities' 30,000 feet of mainline
sewer.
It became apparent that there was
more than enough water infiltration into the main line to warrant
the price of pipe renovation. "Originally, we were concerned
only with the mainline, but the flow monitoring data indicated
that the individual services had problems as well," reflected
ERA president Rodney Beadle.
It was confirmed that the infiltration
problem was not confined solely to the main line. The lateral
services were also contributing to the problem. With this in
mind, Beadle established some recommendations for the renovation
process.
First, it was recommended that the
main line sewer would need to be renovated with an internal
lining. The district required the use of a trenchless renovation
method because the main line ran beneath a boulevard which was
lined with mature trees. Second, general surface disruptions
had to be kept to a minimum. Excessive trenching for lateral
replacement would have a negative social cost.
The county accepted the recommendations
of ERA and asked the firm to design the rehabilitation project
as well as to be involved in the selection, through the bidding
process, of the contractor.
Upon further field study, it was
found that the lateral infiltration problems were the result
of two major factors. Because this was an established neighborhood,
tree root intrusions had developed throughout the service area.
In addition, it was found that some connections had been poorly
installed originally.
In September 1994, Visu-Sewer Clean
& Seal, Inc. of Milwaukee, Wisconsin, was awarded the contract
to rehabilitate the failing sewer system. In its 20th year as
a renovation contractor, Visu-Sewer is familiar with both trenching
and trenchless methods. The company was in a unique position
to compile an effective bid for the efficient renovation of
an entire system, using old and new techniques.
Visu-Sewer successfully installed
U-Liner deformed and reformed PE pipe liner, manufactured by
Pipe Liners, Inc., throughout the entire 30,000 feet of mains.
Next, Visu-Sewer needed to replace the 535 laterals. For this
extensive task, they had bid the job to incorporate both remove-and-replace
methods and pipe bursting methods. "We burst the longer laterals
that run under the street and trenched the short," said Visu-Sewer's
Keith Alexander.
The main ran parallel on one side
of the street. This allowed the option of the traditional trench-and-replace
method for those residents with homes on the same side of the
street as the main, because the main to the house was a fairly
short distance of 40 feet.
Digging up the street and disrupting
local traffic to service those homes on the opposite side of
the street was not an option because of the excellent condition
of the road. Replacing the laterals by trenching would have
left approximately 275 patches on a fairly new street. What's
more, street repairs over the years would result in dips and
possible future additional maintenance.
"We were aware of the pipe bursting
process," stated Alexander. "Knowing what the district wanted,
we talked with the project engineer about how we could be cost-effective
using both bursting and excavation."
To address the lateral replacements
that ran beneath the street, Visu-Sewer elected to use a TT
Technologies' Grundocrack Mini-Atlas pipe bursting tool. This
compact, yet powerful tool was ideal for the job because it
was designed to be launched from a manhole or from small entry
pits. This meant that the street surface would remain intact,
allowing traffic to flow freely. The average distance from point
of origin to termination for these installations was 90 to 100
feet.
The pipe bursting tool was launched
directly into old 6-inch clay pipe, bursting it as the tool
pulled in the new 6-inch PE pipe directly behind. The only excavation
needed to reconnect the services at each house was a small 4-foot
by 4-foot pit. Gerardi Sewer and Water, Inc., based in Norridge,
Illinois, was secured as the subcontractor responsible for executing
the excavations and performing the lateral hookups.
The pipe bursting tool was fitted
with a 7 1/2-inch OD expander to provide ample room for the
safe installation of the new 6-inch PE pipe. As part of the
pipe bursting system, a 5-ton TT Technologies' trailer-mounted
winch was positioned at the exit pit adjacent to each house.
The winch provided the constant line tension to the bursting
tool that is required in the pneumatic pipe bursting process
to help guide the tool through the old pipe.
After each lateral replacement had
been performed, the connections were made at the main by using
a self-sealing neoprene gasket with two stainless steel bands.
This formed a 100 percent seal with the PE liner in the main.
At each house, the PE pipe was attached to the 4-inch cast stub
pipe for a 100 percent seal as well.
The clay ground conditions offered
no complications. Since the bursting tool follows an established
path, soil conditions are generally not a factor. Only in instances
where the pipe has collapsed and become blocked with debris
does the soil become a factor.
The work on the laterals began in
October 1994 and remains in progress with completion slated
for the spring. Winter weather slowed some of the work through
the normal complications associated with sub-zero temperatures.
 Workers
also encountered a few collapsed lines, but for the most part,
residents' service would only be interrupted for a few hours
during the day, with services back in operation by the time
they arrived home in the evening. The compact size of the pipe
bursting tool allowed the Visu-Sewer crew to move from lateral
to lateral very quickly and easily.
TT Technologies' Rich Prosser, the
manufacturer's representative for this on-going project, observed,
"The new Mini-Atlas pipe bursting tool was developed expressly
to meet a specific need--to perform lateral replacements."
As demands change, it is becoming
more and more common to find this type of multi-faceted renovation
of both main line sewer and laterals taking place. Visu-Sewer
has found pipe bursting tools to be a welcome addition to their
arsenal. According to Alexander, "It means that we can offer
our clients yet another means of pipe rehabilitation."
The author is a writer for Lime
Valley Advertising, Inc., Mankato, Minnesota. Grundocrack tools
are protected by British Gas patents.
Trenchless Technology,
April 1995, Pages 38-40
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