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Trenchless Sewer Main Replacement
Enviro-Flow Takes Pipe Bursting Back to School

by Jim Schill

When the benefits of trenchless pipe bursting are discussed, key phrases like no-dig, minimal disruption, cost savings, increased capacity and environmentally friendly are often heard. The images they conjure are immediate: a beautifully landscaped yard left unharmed, a roadway that remains open to traffic, boulevard trees untouched. Chalkboards, desks, computers and lockers don’t immediately come to mind. They did recently for Tim Evans, however. Evans, wastewater division manager for Enviro-Flow Companies, Zanesville, OH, was recently approached by school officials at the Guernsey-Noble Vocational School in Senecaville, OH, about problems with a sanitary sewer main. The main traveled directly underneath the school and had been plagued by reoccurring blockage. Evans said, "An open cut project was not the best option. With the amount of potential disruption inside the school from an open cut application, we suggested a trenchless replacement option, pneumatic pipe bursting." For the bursting project, Evans chose the Grundocrack pneumatic pipe bursting system from TT Technologies. TT Technologies’ pipe bursting specialist Mark Maxwell was contacted for technical support.

Experienced Contractor


The 150-ft sewer main ran beneath the school, traveling under the school’s kitchen and several computer classrooms. Trenchless pipe bursting was chosen to minimize disruption and costs.

Enviro-Flow Companies was founded in 1976. The company provides industrial and municipal water and wastewater services throughout the state of Ohio. Over the past 25 years, the company’s services have grown to include, among others, pipe line televising and inspection, I & I studies, sewer cleaning, electronic pipe location, manhole rehabilitation and, most recently, pipe bursting. Evans said, "Enviro-Flow Companies has two divisions. First, Enviro-Flow Service Co. serves all of Ohio. This division takes care of commercial, industrial and municipal customers. Second is a plumbing and drain service. That division takes care of residential and commercial customers for Licking, Muskingum, Guernsey, Perry, Morgan and Noble counties." Enviro-Flow would tackle the troubled sewer main at Guernsey-Noble Vocational School.

Tuberculated Line

Enviro-Flow Companies selected a 5.75-inch diameter pneumatic Grundocrack PCF 145 from TT Technologies for bursting the cast iron main. Note the long guide head on the front of the tool. Equipped with cutting blades, the guide head is one component that makes bursting cast iron possible.

The combination 4- and 6-inch diameter cast iron sewer main was installed when the school was built in 1969. Over the past several months the line experienced numerous backups and forced school officials to take action. Evans said, "The line kept plugging up. We’d go up there and jet it; clean it out. Finally it got to the point where I said, ‘Listen, this is silly. Let’s televise it and see what the problem is and see if we can’t get this fixed.’ After looking at the line, we recommended that it be replaced." The 150-foot section of main ran below the school’s kitchen area and crossed under several computer classrooms. Approximately 60 feet of the main was 4-inch diameter cast iron, and the remaining 90 feet was 6-inch cast iron. Seven lateral connections also needed to be excavated and replaced. One of the most challenging aspects of the job, however, was overcoming the host pipe material, cast iron.

The pneumatic pipe bursting tool enters the launch pit. Approximately 60 feet of the run was upsized from 4-inch cast iron to 6-inch HDPE. The remaining 90 feet was replaced size for size, 6-inch cast iron to 6-inch HDPE.

Tool Configuration

Cast iron pipe tends to break several feet in front of a standard pipe bursting tool. This causes the potential for two major problems. First, the shards of cast iron pipe are sharp and can actually cut winch lines. Second, pipe fragments can build up making the host pipe impassable. This can cause the pneumatic pipe bursting tool to change direction and veer off course. Essential to the success of the job was the use of a guide head or "schnozz." The guide head is attached to the front of the pipe bursting tool and adds needed tool length. Because the guide head is smaller in diameter than the host pipe, it guides the tool and allows it to get into the pipe and break it at its weakest point, the inside. Besides adding tool length, the guide head helps protect the winch line. In many configurations, the winch line is connected to the front of the guide head instead of the front of the tool. This keeps the line ahead of the actual bursting and out of the way of shards of pipe. Maxwell said, "Cutting blades can be used in conjunction with a guide head. The blades are welded directly to the guide head. The blades focus the percussive action of the tool and greatly enhance overall bursting power, allowing the tool to successfully burst difficult host pipes, like cast iron as well as many point repairs like PVC."

Site Prep

The exit pit was located outside of the building. The new HDPE section was connected to the remaining cast iron section with a mechanical joint. The cast iron main traveled an additional 90 feet where it tied into a manhole.

Work began on the project in mid July. The Enviro-Flow crew used a TT Technologies 5.75-in. diameter Grundocrack PCF 145 pneumatic pipe bursting system, equipped with an 7-in. rear expander and a specially-designed guide head with cutting blades for cast iron pipe. A 10-ton Grundowinch was used to guide the bursting tool through the host pipe. According to Maxwell, the Grundowinch also played a key role. Maxwell said, "The Grundowinch provides constant tension at variable speeds. It is able to compensate for changes in bursting speed and is able to prevent slack from developing in the line. This ensures a smooth bursting operation." The Enviro-Flow crew dug a 4-ft. by 12-ft. launch pit inside the school with a mini excavator. Evans said, "The excavator is extremely compact, just 36 inches wide. In this situation it allowed us to get into areas that normally we’d need to dig by hand. It definitely saved us time." The launch pit was located beside the kitchen. The gravity-fed line was approximately 50 inches deep at the start of the bursting run and 72 inches deep at the end. The crew fused 150 feet of 6-inch High Density Polyethylene (HDPE) pipe and staged it through the kitchen area to the outside of the building. The exit pit was dug at the end of the run, outside, 150 feet away. The 10-ton Grundowinch was placed at the exit and bursting was ready to begin.

Bursting in Action

Bursting operations went extremely well. The entire 150-foot run was completed in just 30 minutes. Evans said, "One of the school’s officials wanted to come down and watch the pipe bursting in action. We told him we’d be ready to go around 2:00. Well he was running a little behind schedule and called when he was ready to come down. We had to tell him that the pipe was already in the ground!" After the burst was complete, the Enviro-Flow crew tied in the seven lateral lines using service saddles and specially designed tee connections for HDPE pipe. Each lateral connection took approximately one hour to complete. The new HDPE section of main was connected to the remaining section of cast iron pipe with a mechanical joint adapter. The remaining section of main traveled an additional 90 feet before tying into a manhole.

Bursting Benefits

School officials were extremely pleased with the results of the pipe bursting project. Evans said, "Pipe bursting the project probably saved us two to three weeks over an open cut. Plus it would have been a lot more expensive for the school if they had to go in there and replace carpet, replace a bunch of tile, and disconnect and move all the computers. We were able to save the school a tremendous amount money and time through pipe bursting." Note: Advantica, formerly British Gas, owns the method patent on pipe bursting.

A bird’s eye view of the bursting operations. The school was able to avoid costly restoration through the use of trenchless pipe bursting.

 

Cleaner, October 2001