Pipe Bursting: Making A Trenchless Impact
In an industry where some things never change and others change all the time, some of the most significant technology breakthroughs have occurred. Over the last 20 years the pipe rehabilitation and replacement industry has seen the development and refining of trenchless construction equipment, methods and techniques. This is undoubtedly one of the most significant accomplishments the industry has experienced. While directional drilling saw an incredible boom in the 1990s, another trenchless method has made an amazing climb in popularity and use over the last 20 years, pipe bursting.
Pneumatic pipe bursting was developed from the concepts found in pneumatic piercing tools. These tools have been widely used since the 1960s. When DJ Ryan and Sons LTD and British Gas (now Advantica) successfully burst a cast iron gas main by using a piercing tool in England during the late 1970s, pipe bursting was born.
After months of research, development and field tests, Ryan and British Gas patented the method. In addition to British Gas’ 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
Dave Holcomb, Vice President of trenchless equipment manufacturer TT Technologies, Aurora, Ill., has been a key figure in the introduction and development of pipe bursting in the United States and North America. He said, “Because small diameter directional drilling was developed in the U.S., 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, for the most part, 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 1990s. The Hall Albert Construction Company of Fort Worth, Texas completed a pipe burst early in 1992. According to Holcomb, that was the start and things took off from there.
Inflow & Infiltration
Coastal regions, areas that receive significant rainfall and areas with high water tables, suffer the worst problems with inflow and infiltration. Not coincidentally, these are the pockets around the United States and North America where pipe bursting first took hold.
During the mid- to late-1980s, some pipe bursting work was done on the east coast, but it was Houston, Texas, that became the epicenter for pipe bursting in the U.S. and North America. Holcomb says, “Houston has really taken an aggressive stance on improving their sanitary sewer infrastructure. They have led the way for pipe bursting in this country. Houston grew quickly in the late 50s and 60s. During that time, many different types of pipe went into the ground. The ground condition there does not lend itself well to some of those pipes.”
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 soundest approach to meeting federal, state and municipal standards. By replacing existing sewer lines with High Density Polyethylene Pipe, they are ensuring that their sanitary sewer system is watertight and free from the I & I problems that contribute to the need for larger treatment facilities.
Holcomb maintains that the work that was done and is still being done in Houston made the JEA Project in Jacksonville, Fla. possible.
Pneumatic Pipe Bursting:
The 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 that 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.
The winch system is very integral to the pneumatic pipe bursting process. Holcomb said, “The winch needs to provide constant tension at variable speeds. That is especially important for projects with point repairs. When the bursting tool reaches a repair it slows down as it works its way through. After the repair is burst, there is less resistance and the tool speeds up quickly. The a constant-tension, dual-capstan, twin-motor winch will compensate for this change in speed and prevent slack from developing in the line.”
With the use of expanders, one pneumatic bursting 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 the upsizing of the existing pipe. Expander and tool configuration can mean the difference between failure and a successful pipe burst. A very common and effective configuration is a pneumatic bursting tool with a rear expander.
Tool and expander selection is affected by various factors including host pipe type, depth and profile, jobsite layout, burst length, soil conditions and more. Upsizing is also a major consideration in tool expander selection. Some extremely large upsizes in the 120-125% range have been successfully completed through bursting. According to Holcomb, 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
It is important to keep the aforementioned factors in mind before pipe bursting. Holcomb says, “It’s best to evaluate pipe bursts on a job-by-job basis. Each job has unique characteristics and situations that have to be taken into consideration before a burst is attempted.”
Static Pipe Bursting
According to Holcomb pneumatic bursting works well with a wide variety of fracturable host pipe materials and diameters, ductile iron and steel pipes have been a limitation of the pneumatic method. In the United States the demand for pipe bursting grew in the sanitary sewer market, but didn’t in the water and gas markets because of the abundance of ductile iron and steel pipes.
Holcomb said, “That is beginning to change with the introduction of the hydraulically powered static pipe bursting systems. The static systems give contractors the ability to split and replace ductile iron, steel and lined pipes with the same size pipe or larger.”
During the static bursting process, specially designed bladed rollers are pulled through an existing line by a hydraulically powered bursting unit. As the bladed rollers are pulled through, they split the host pipe. An expander attached to the rollers forces the fragmented pipe into the surrounding soil while simultaneously pulling in the new pipe.
The bladed roller configuration is an essential part of the static bursting success. The specially designed bladed rollers actually split the host pipe instead of ripping or tearing it. This is a clean process and prevents potential damage to the product pipe.<
Patented Quicklock bursting rods are easily and securely linked together not screwed together like traditional drill stems or other static systems. This system speeds the installation process as well as the breakdown procedure. The rods can be quickly removed one at a time at the exit pit as bursting is in operation. When linked together the rods form a flexible chain that allows for bursting around bends or sweeps in the line.
For longer lengths of pipe or runs with slight bends, the project can be divided. A 1,000-foot run for example, can be divided into two 500-foot sections with the bursting unit placed in the middle.
Static bursting’s biggest arena could end up being the water market. According to Holcomb, studies are showing that the country’s water infrastructure is in as bad of shape, if not worse, than the sewer infrastructure.
While replacing large diameter sewer mains has helped mitigate the problems associated with I&I, in most cases it has not solved them. Attention is being placed on lateral service line replacement and municipalities are discovering that between 40% and 60% of all infiltration can be attributed to deteriorated lateral services. Additionally, lateral sewer lines already face tremendous problems associated with tree root intrusion, a problem that is adding to the push to replace lateral services.
Many communities are starting to mandate lateral testing and replacement. Dividing the cost of lateral replacement between the homeowner and the municipality is becoming more common as well. And since trenchless pipe bursting is one of the easiest, efficient and effective ways to address the lateral rehab and replacement issue, it has become a focal point in this latest battle against I&I.
Holcomb said, “Offering homeowners a trenchless option that can mitigate damage to trees, driveways, sidewalks and landscaping can help soften the blow. In the urban setting when there is little right-of-way and a lot of concrete and asphalt, trenchless lateral pipe bursting can have a tremendous impact by limiting cost and disruption.”
Holcomb also noted that improvements in lateral bursting equipment have made the method accessible to everyone from specialty to general contractors. He said, “The new lateral bursting equipment is very portable, but doesn’t compromise on power. It’s also easy to use. Both static and pneumatic lateral bursting systems can be easily transported in most pick-up trucks. They only require a minimal crew compliment to operate. And they really get the job done well. With the big push for lateral replacement, the timing of some of this equipment couldn’t be better.”
by Jim Schill
JEA, Supplement for Trenchless Technology, November 2004