Editor’s Note: The International Pipe Bursting Association (IPBA), a division of NASSCO, is presenting a series of articles in Underground Construction that will provide the reader with a better understanding of the technology. Many myths and misconceptions exist regarding this proven rehabilitation method for replacing existing underground utilities.
Pipe bursting is a technology that has matured in North America since the early 2000s. Although this technology has been proven internationally and more so domestically, there are many common myths and/or misconceptions that exist in regards to the technology and its practical application. In January 2012, the IPBA released a guideline for pipe bursting that provides support and reference to the items discussed in this article.
Myth #1: Pipe bursting is expensive. — Cost is a relative term and is often used out of context when comparing the use of alternative or trenchless methods like pipe bursting. In the early 2000s, the majority of pipe bursting projects in many regions of the country consisted of small quantities and were driven by a mentality that pipe bursting was only applicable where you could not dig. The result was a period of time where relatively high unit costs existed and were then assumed to be comparable costs to any size project.
With small projects, many contractors did not own equipment and had to rent and ship to the job site which inflated the unit cost on a small quantity job. Since pipe bursting has grown, contractors often now own the equipment required to perform most projects. Municipalities are seeing the benefits of using pipe bursting as an alternative to open cut, cured-in-place pipe (CIPP) or cement mortar lining and by awarding more projects of larger quantities are seeing significant savings by utilizing pipe bursting. A significant benefit to pipe bursting and other trenchless technologies is that when all costs are added including contract, social and environmental values, the true costs of pipe bursting are very competitive with other technologies.
Myth #2: Pipe bursting should only be used when the pipe CANNOT be excavated. — Pipe bursting should be considered when any of the following conditions exist:
• Pipe to be replaced is in a high traffic area;
• An environmentally sensitive area;
• Surface restoration costs are high;
• Disruption to the general public and local business is undesirable;
• A reduction in emissions from the project is beneficial;
• Replacing the existing pipe in the same corridor without establishing another utility easement;
• A reduction in construction schedule is desired; or
• Any utility replacement project where an alternative method would increase competitiveness of bidding is desired.
Myth #3: Pipe bursting and CIPP are comparable technologies. — CIPP is and will be a proven and reliable rehabilitation technique. However, pipe bursting is a pipe replacement technique where a new factory manufactured pipe is installed and replaces the existing pipe. CIPP relines the existing pipe forming to its internal diameter and shape. Pipe bursting will install a new pipe that has a true ID and eliminated offsets, deflections or other pipe deviations that CIPP would not.
Myth #4: Pipe bursting is only practical when you need to increase the size of the pipe. — A significant amount of pipe bursting completed in the United States is for “size on size” replacement where additional capacity is not required. Although pipe bursting does have the ability to increase the ID of the existing pipe, it is a very practical and widely used method for replacing existing pipe with a same-sized product.
Myth #5: Pipe bursting is only practical where there are a small number of service connections. — The number of service connections on a pipe bursting project, whether it is for sewer, water or gas replacement, will increase cost and add excavation. However, even with a significant number of service excavations required, the total reduction of excavation can exceed 80 percent and the project cost be significantly lower than that of open-cut excavation. Although technologies like CIPP can reinstate service connection robotically with no excavation, many owners find that by excavating during a pipe bursting and installing a new “hard connection” to the new mainline, the results of reduced infiltration and inflow or water loss is worth the additional expense and effort.
Myth #6: If pipe bursting involves excavation why is it called trenchless? — Unlike some technologies that can rehabilitate a pipe by the use of “no-dig” technology, pipe bursting can be defined as “less trench.” Dependent on the method employed and the size of the product pipe being installed pipe bursting can reduce the total excavation by as much as 95 percent and most commonly be 85 percent or more when compared to open-cut excavation.
Myth #7: You cannot pipe burst potable water mains. — Pipe bursting of potable water mains is wildly popular in Europe and beginning to gain significant acceptance in North America. Typical water mains constructed of cast iron, asbestos cement or plastics can be burst with relative ease utilizing pipe splitting techniques which allows a new pipe with increased capacity to be installed.
Myth #8: You can only install HDPE pipe with pipe bursting. — Although HDPE is the most commonly used material installed by pipe bursting for water, sewer and gas applications, advancements in materials like thermally fused PVC, restrained joint PVC, restrained joint ductile iron and others now allows a variety of pipes to be installed by pipe bursting. Although HDPE pipe is the only pipe material that can be installed utilizing pneumatic pipe bursting methods, others can be installed utilizing static pipe bursting.
Myth #9: Pipe bursting will heave the ground above it. — Pipe bursting displaces soil as an expander head is pulled through the ground which opens up the diameter of the existing pipe ID to allow insertion of the new pipe. The expansion will vary by the geotechnical conditions around the existing pipe, but in most cases the soil will expand upwards and outwards from the invert of the existing pipe. If the soils are either uncompressible or the volumetric displacement upwards is more than the minimum depth of cover calculation, then the potential for heave exists. However, the potential for ground heave can be calculated prior to performing a burst and is rare in most installations where class A-B conditions occur.
Myths and misconceptions are often driven by lack of education or lack of first-hand experience. The IPBA has at the core of its mission the need to provide non-biased information, reference and real world case studies to municipal utility owners and consultants who are looking for alternatives to replacing its underground infrastructure. 2012 IPBA Guidelines for Pipe Bursting are available for a free download at www.nassco.com, and can be used to educate those who need additional information regarding pipe bursting uses and practical applications.
Coming in April: Update on IPBA pipe bursting installation guidelines.
FOR MORE INFORMATION:
IPBA (NASSCO), (410) 486-3500, www.nassco.org