By Jim Schill

In the trenchless industry, innovation and creativity flourish. Contractors are constantly finding new uses for established tools. Engineers and manufacturers are continually developing new and more efficient tools and methods. The industry is also need driven, with no two jobs ever quite the same.

In the early 1980s, these factors contributed to the development of a new pipe replacement method. Almost 20 years later, pipe bursting is still revolutionizing the way pipe replacement is done around the world.

BURSTING BACKGROUND
Pipe bursting was developed from the concepts behind pneumatic piercing tools. These tools have been widely used since the 1960s. When DJ Ryan and Sons Ltd. and British Gas successfully ran one through an existing gas line in England in 1981, pipe bursting was born.

After months of research, development and field tests, Ryan and British Gas patented the method. "British Gas had a need, on a massive scale, for cast iron pipe bursting," says Carola Schmidt of Tracto-Technik. "With the use of Tracto-Technik equipment, DJ Ryan and British Gas really debugged the method."

In addition to British Gas’s need for pipe bursting, a substantial amount of cast iron piping, already in place throughout Europe, was failing. Both the gas and water markets in Europe were ripe for small-diameter pipe bursting. The situation was different in North America, where the sewer industry is pipe bursting’s strongest market. In the sewer industry, contractors utilizing pipe bursting can efficiently replace and upsize existing lines without trenching.

BURSTING IN NORTH AMERICA
TT Technologies Inc. of Aurora, Ill., a wholly owned subsidiary of Tracto-Technik, is a leader in pipe bursting. TT Pipe Bursting Product Specialists Dave Holcomb, Mike Schwager and Eddie Ward have been instrumental in introducing and developing pipe bursting in the United States and North America. The three agree it has been a challenge, but the reliability of the method and the quality of the tools has made believers out of countless contractors, engineers and municipalities.

"Because small-diameter directional drilling was developed in the U.S.," says Holcomb, "the need for pipe bursting small-diameter cast iron gas pipe hasn’t been there. Contractors drilled parallel to the old line and pulled in polyethylene. The need for pipe bursting in the gas industry was all over before it started."

Holcomb says he first started getting calls about pipe bursting in 1983. The big push in the marketplace, however, did not begin until the late 1980s and early l990s.

The Hall Albert Construction Co. of Fort Worth, Texas, completed a pipe burst upsize for the Trinity River Authority early in 1992. The job called for replacing 2,650 ft. of 10-in. reinforced concrete sewer pipe with l6-in. iron pipe size polyethylene. Hall Albert used a 10.5-in.-diameter Grundocrack Gigant and successfully completed the upsize in rocky clay soil. "After the Hall Albert job," notes Mike Schwager, "the door opened wide in Texas."

HOUSTON
During the mid- to late-1980s, some pipe bursting work was done on the East Coast, but it was Houston that became the epicenter for pipe bursting in the U.S. and North America. "Houston has really taken an aggressive stance on improving its sanitary sewer infrastructure," Holcomb says. "The city has led the way for pipe bursting in this country."

Houston city leaders also know that they have to meet Clean Water Act standards regarding treatment facility discharge levels. While many cities around the country are scrambling to build bigger wastewater treatment facilities, Houston may have the most sound approach to meeting federal, state and municipal standards. By replacing existing sewer lines with high-density polyethylene (HDPE) pipe, they are ensuring that their sanitary sewer system is watertight and free from the inflow and infiltration (I&I) problems that contribute to the need for larger treatment facilities.

MOVING UPSTREAM
In the United States during the ‘70s and ‘80s, billions of dollars worth of water treatment plants were built to solve discharge problems. However, those plants only added treatment capacity. It was soon realized that despite this additional capacity, the plants were still filling up with water they were unable to treat.

Civil engineers are now looking upstream to solve their treatment problems. "They’re replacing big-diameter and small diameter mains," says Eddie Ward. "Eventually, they’re going to work all the way back to the house. The most efficient method to replace and upsize these lines is pipe bursting."

Coastal regions, areas that receive significant rainfall and areas with high water tables suffer the worst problems with I&I. Not coincidentally, these are the pockets around the United States and North America where pipe bursting first took hold.

TOTAL SYSTEM REPLACEMENT
Mansfield, Wash., is a good example of a municipality that turned to pipe bursting to solve its I&I problems on a large scale. In Fall 1995, the city was facing tremendous flow problems with its sanitary sewer and knew those problems were related to I&I. After videotaping the lines, the city discovered that its 1950s concrete sanitary sewer system had decayed and suffered from extensive tree root infiltration. The entire system, consisting of 18,000 ft. of sanitary sewer, needed replacement and more than 3,000 ft. needed to be upsized.

Pipe bursting was chosen for several reasons. First, the method is trenchless. Disruption to city streets, lawns and businesses is minimal. Second, pipe bursting is the only trenchless method of rehabilitation or replacement that allows for the upsizing of existing lines. Third, the new HDPE pipe is strong yet flexible, making it ideal for tough installations. Finally, it is economical. With a population of a few hundred people, Mansfield’s financial resources were limited. The pipe bursting bid came in $210,000 less than open-cut trenching. These factors are what make pipe bursting so attractive.

PIPE BURSTING INVESTMENT
Decaying infrastructure and fiscal responsibility has prompted some municipalities, like the city of Columbus, GA., to purchase pipe bursting equipment. In late 1997, it was determined that more than 20,000 ft. of sanitary sewer in Columbus would need to be replaced and/or upsized over the next 5-10 years. Rather than bidding out portions of the job over time, the city chose to do the work itself.

Columbus Water Works purchased a pneumatic 8.5-in.-diameter pipe bursting system. The system included the tool, a 10-ton constant-tension winch and rear expanders for 8- and 12-in. HDPE. The purchase will allow the city to carry out its development plan, without undue financial impact on the approximately 200,000 residents.

SPHERES OF INFLUENCE
Pipe bursting awareness and usage has spread concentrically outward from the pockets of heavy usage around the U.S. and North America. "It’s gradually radiating out," says Holcomb. "In the areas that are familiar with pipe bursting, we’re starting to see bigger volume jobs. It’s not unusual to have a 50,000-ft. job bid today and maybe another 33,000-ft. job bid tomorrow."

"They have to see it," adds Ward. "There’s no doubt about that. Once they see it and see that it works, they’re willing to try it. A 400-ft. job will eventually lead to a 5,000-ft. job and ultimately a 10,000-ft. job over time."

The method is so well regarded in certain areas that many jobs are being bid specifically as pipe burst only. Many of these bursting-specific jobs are upsize projects. In fact, some of these jobs involve bursting lines that are still integral, but are just too small to handle current flow levels. In situations where a municipality merges its sewer system with another community's system and an 8-in. line joins two 12-in. lines, a bottleneck can occur. That 8-in. line is a perfect pipe bursting candidate.

Re-zoning is sometimes an impetus for bursting perfectly capable lines that don't have the capacity for increased usage. For example, a city rezones a residential area for development of high-rise condominiums. The existing lines are only able to handle small residential structures. Perfectly integral lines may need to be replaced. Upsizing to meet new capacity requirements can be accomplished quickly and economically through pipe bursting.

BURSTING THE BARRIERS
The biggest stumbling blocks to the continued growth of pipe bursting as a method for pipe replacement and upsizing are lack of exposure to the method and willingness to try it. "We try to educate everyone the best we can," says Holcomb. "However, there is still a general lack of familiarity with the method on the engineering level and municipal level."

"Even though it's been around for almost 20 years," he adds, "in the U.S. and North America, it's a relatively new technology, much like directional drilling was. Today, directional drilling is an established process. Now, pipe bursting has to get there."

Pipe bursting sometimes faces legal challenges as well. Jobs done in the private sector will usually require some type of city or municipal approval. More often than not, there are no city ordinances that specifically allow for the use of pipe bursting. Others, however, do permit the use of such new technologies.

THE PIPE
Even if there is an acceptance of pipe bursting, the engineer or municipality has to be comfortable with the use of HDPE pipe. "Once we overcome the reluctance to pipe burst," Holcomb adds, "we have to overcome the reluctance to use a product pipe that many are not familiar with. Many engineers are used to working with ductile iron or polyvinyl chloride (PVC). Educating them on the benefits of using HDPE is just as important as exposing them to pipe bursting."

Again, assuaging fears is done through testimonial. "We usually try to get them involved with people that have had pipe bursting done for them," Schwager says, "be it a customer at the municipal level, a contractor or another engineering firm. In most cases, they'll talk to all of them."

HDPE was developed in the 1950s. Currently, it captures about 85% of the market share in the gas industry in the United States. In Europe, it dominates the water market. Industries are turning to HDPE for several reasons.

First, HDPE is zero-leak piping. Sections of HDPE are fused together to make the desired length of pipe. Joints are not required with HDPE. "It's estimated that 10% of all potable water for the average utility is lost due to exfiltration or leakage," Kirchdorfer says. "For utilities that need to show a profit, that's nonbillable water. And for the others it's wasted water." In addition, zero-leak piping for a sanitary sewer system can greatly mitigate I&I problems.

Second, HDPE is flexible. HDPE pipe can be safely and quickly installed in difficult and cramped job sites.

Third, HDPE is durable. "While HDPE is conservatively rated for a 50-year life span," Kirchdorfer notes, "many believe that its actual life span is over a hundred, maybe several hundred years."

PNEUMATIC PIPE BURSTING: THE PROCESS
Hydraulic and static pipe bursting equipment is common. However, a majority of pipe bursting done in the United States is done with pneumatic tools. During pneumatic pipe bursting, the pipe bursting tool is guided through a fracturable host pipe by a constant- tension winch. As the tool travels through the pipe, its percussive action effectively breaks apart the old pipe and displaces the fragments into the surrounding soil. Depending on the specific situation, the tool is equipped with an expander, which displaces the host pipe fragments and makes room for the new pipe. As the tool makes its way through the host pipe, it simultaneously pulls in the new pipe, usually HDPE (Figure 1).

THE TOOL
According to patent holder British Gas, hydraulic, static and pneumatic pipe bursting tools are available from six licensed manufacturers in the United States. With the use of expanders, one tool can be used to burst several different size host pipes and replace them with new HDPE pipes of the same size or larger. Pipe bursting is the only trenchless method of rehabilitation and replacement that allows for upsizing of the existing pipe.

THE EXPANDER
Expander and tool configuration can mean the difference between failure and success in pipe bursting. A very common and effective configuration is a pneumatic bursting tool with a rear expander.

Tool and expander selection is affected by various factors. First, is the host pipe fracturable? Fracturable host pipes include concrete, reinforced concrete, clay, cast iron and transite. PVC and acrylonitrile butadiene styrene (ABS) plastic pipe offer some bursting potential. With PVC and ABS, special cutting blades are necessary and the length of runs may be reduced. In part, different expander tool configurations are chosen based on the material, size and usage of the host pipe, as well as its depth and profile Point repairs made to the host pipe may also affect bursting potential.

Second, consideration must be given to the layout of the work site. Some jobs require both a launch and exit pit. Other jobs are manhole launched and removed. Still other jobs burst from a launch pit to a manhole. The tool is then reversed out through the newly installed product pipe. This eliminates the need for an exit pit.

Third is the required burst length. In most sewer replacement applications, the burst length is usually manhole to manhole. Long bursts with large-diameter product pipes may require bigger tools and the addition of polymer or bentonite.

The fourth consideration is the terrain and soil conditions. Most favorable bursting projects involve pipes that were originally installed by trenching or open cut because the fill material surrounding them is usually conducive to pipe bursting. Some soils, like beach sand, will not remain in the expanded state long enough for new product pipe to be installed.

Upsizing depends on the soil conditions as well. "We've run into extremely rocky soil conditions where the trench was basically carved out of the rock," Schwager says. "The pipe was nearly the same size as the trench, and the whole thing was back filled. An upsize in that situation is not feasible."

The fifth issue is the product pipe size. HDPE is the most common new pipe material. Because of the weight of larger diameter HDPE, bentonite is used to reduce friction. Tool and expander configurations are influenced by product pipe size.

According to Schwager, TT Technologies has done some extremely large upsizes in the 120-125% range. These bursts are categorized as experimental and out of the ordinary, although quite a few have been completed successfully. The 25-50% upsize is much more common, but is still challenging. Upsizes between 0% and 25% are considered common.

ON THE JOB
It is important to keep the aforementioned factors in mind before pipe bursting. "It's best to evaluate pipe bursts on a job-by-job basis," Holcomb comments. "Each job has unique characteristics and situations that have to be taken into consideration before a burst is attempted."

Schwager, Ward and Holcomb agree on the importance of videotaping the line before the run. "A good way to ensure a successful burst," says Ward, "is to identify potential problems and remedy them before bursting." Shooting video of the line before the job is key.

Certain pipe materials and particular joint configurations are not burstable or are difficult to burst, at best. "Every day we see joints and point repairs we're unfamiliar with," Schwager says. "Some are burstable, others are not. In either case, we need to know what we're dealing with up front. That way, we can avoid potential problems by making the right decisions before going ahead. Often times, that means tool choice and configuration." Typically, cast iron bell and spigot joints are burstable. Some bolted, flange-type joints, as well as ductile iron point repair sections, are burstable through the use of guide head (schnozz) technology.

BURSTING AHEAD
The future looks bright for pipe bursting in North America. There are countless municipalities with aging infrastructures that can benefit from pipe bursting. There is also opportunity for growth in the water market.

According to Kirchdorfer, HDPE was approved for water by the American Water Works Association in the United States in the early 1990s and is now gaining acceptance in the potable water market. "While the water market is much bigger than the sanitary sewer market," says Holcomb, "it's in its infancy when it comes to pipe bursting. Bursting will eventually become more common in the water market."

The industrial sector has embraced pipe bursting rather quickly. According to Ward, what is considered industrial is usually sanitary in an industrial setting. "Pipe bursting in the industrial market is often emergency driven," he says. "Usually, the sanitary sewer has deteriorated and is backing up. Plant managers are looking for a way to fix the problem quickly, without tearing up the floor and shutting down the plant. Pipe bursting is the solution."

As the method gains exposure, acceptance and eventually preference, pipe bursting will be the solution for many pipeline problems.

Pipeline Digest, Winter 1998, Pages 14-19