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 mature technology used to replace existing underground utility lines. Some of the most common questions owners and engineers have when considering pipe bursting are “what types of pipes can be burst?” and “what types of pipes can be installed by pipe bursting?” This article will provide insight into answering those questions as well as highlight some of the design and practical considerations that need to be accounted for on any pipe bursting project.
First and foremost when considering any pipe bursting project, it is important to identify the type of material of the existing pipeline. Over the last 100-plus years, gravity and pressure pipes have been installed made of wood, brick, clay, iron, cement, asbestos cement and plastics as well as other less common types and variations of these pipe materials. Pipe types like PVC truss pipe, Perma-Strand and others are trade names and these “hybrid” types of pipes should be identified clearly in the planning stage of a project as they should be looked at differently in some cases than more common pipe types.
Pipe bursting must fracture and split the existing pipe. Therefore, pipes are most often classified as “fracturable” or “non-fracturable” and that helps determine both the method of pipe bursting that can and should be used as well as the type of “burst head” or “splitter” that will be necessary to properly “burst” the pipe. Nearly all pipe types can be safely burst if considerations are made for how they will react to the bursting process.
The most common types of gravity sewer pipes burst and replaced are: vitrified clay pipe (VCP), asbestos cement (AC), concrete pipe (CP) and PVC. With a properly designed pipe bursting system, materials such as reinforced cement pipe (RCP) and even brick can be burst very successfully. In municipal water main replacement, which is widely popular overseas and gaining more acceptances in North America, CI, AC and DI are the most common pipe types being replaced. These pipes must be “split” and not necessarily “burst.” However, the process is very similar to that of a fracturable pipe. This is often referred to as pipe splitting but is simply a different attachment on the front of the pipe bursting tooling.
Pipes that require special attention and are, in most cases, still considered experimental, are CMP, large diameter brick among others. CMP, for example, does not typically burst or split very well. However, there is work being done daily to help overcome this and make bursting of CMP a viable option.
The most common type of pipe installed with pipe bursting, much like HDD, is overwhelmingly HDPE. However, advancements in other pipe types have made installations of those much more common. HDPE can be installed as a gravity or pressure pipeline and is very flexible and forgiving which gives it a tremendous amount of versatility in the field. Most trenchless installation crews are experienced in how to properly handle, fuse, and install it which always makes it a favorite of contractors. Learning the difference between IPS ( iron pipe size) and DIPS (ductile iron pipe size) and the appropriate DR value required to install it and the relationship that has to actual ID, is always challenging to owners and engineers unfamiliar with the product. HDPE pipe can be installed by static or pneumatic pipe bursting methods.
Advancements in PVC products from restrained joint to fusible PVC have helped make pipe bursting an option in communities where they prefer PVC pipe. Restrained joint PVC pipe can be installed by a cartridge type installation which reduces the footprint of a project in a congested area, and fusible PVC is installed through a continuous installation similar to that of HDPE. PVC pipes can only be installed by static pipe bursting.
Ductile iron is a standard in many utility systems and is also a product that can be installed by pipe bursting. Special restrained joints allow for the pull loads required to install the pipe. However, installations require special considerations due to the need for a bell and socket style joint. DI pipe can only be installed by static pipe bursting and can be done through a cartridge style pit or a continuous installation.
Projects involving the installation of materials like VCP, FRP, steel pipe and others have been accomplished and can be considered, although you should consult with the pipe manufacturer prior to installing.
The most important thing to understand when considering or planning a pipe bursting job is that special considerations must be made for the pipe types that are being replaced and installed. Consulting with a pipe manufacturer, pipe bursting contractor or system manufacturer is a great way to assist in design considerations as they will often have the best real world experience and will be able to make recommendations on how best to design a constructible project. IPBA member companies have the experience and knowledge needed to help you consider and evaluate pipe bursting as a practical trenchless construction method. There are thousands of case studies available so you can be assured that the means and method you are considering is a proven approach.
Through continued education involving utility system owners, engineers, manufacturers, contractors and field crews, pipe bursting can continue to become a method of choice for rehabilitating failing underground infrastructure in your community.
Next up: Pipe bursting geotechnical considerations.
FOR MORE INFORMATION:
IPBA (NASSCO), (410) 486-3500, www.nassco.org