Small Bursting Tool has Big Impact on Lateral Installations
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.
by Jim Johnson
Trenchless Technology April 1995, Pages 38-40