Product Pipe Choice: Static Pipe Bursting Grows to Meet the Needs of the Market
Over the last decade, the trenchless static pipe bursting method has become one of the most effective and preferred trenchless methods for replacement or upsizing of aging gravity sewer, water mains and storm drains. Hydraulically powered static pipe bursting systems have given engineers and contractors the ability to split and replace ductile iron, steel and lined pipes, as well as pipes with ductile iron and steel repairs. Initially this made the method attractive to many areas with miles of failing ductile iron or steel pipes. Traditionally, high-density polyethylene (HDPE) was the primary product pipe option for the static bursting method. While HDPE is a solid product pipe option, certain municipalities are vested in other types of pipe materials, which ultimately limited the reach of the static bursting method.
Recently, significant advancements in the method have made it more versatile than ever before. Various pipe manufacturers have been working with pipe bursting equipment manufacturers to find real world ways to adapt their pipe products to pipe bursting installations. Results have been extremely positive and some of industry firsts have made contractors and engineers take notice.
Static Pipe Bursting Overview
During the static bursting process, specially designed bladed rollers are pulled through an existing line, attached to bursting rods, 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.
Preferable bursting rods are linked not screwed together like traditional drill stems or other static systems. This system plays a large role in the use of various product pipe materials and 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. The bladed roller configuration is an essential part of static bursting success for steel and ductile iron pipe materials. 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.
Utilizing Sectional or Segmented Pipe
Segmented pipe is assembled one joint at a time in a “cartridge loading” process. It is described this way because of the similarities between a rifle cartridge providing bullets to the rifle chamber and the segmented pipes being lowered and assembled in the launch pit. It is well suited for locations where available space for pipe lay down is not available
Segmented or sectional pipe can be roughly placed into two categories, restrained joint and non-restrained joint. Each type requires a different approach when used in conjunction with static bursting. Installing sectional pipes with restrained joints through static pipe bursting, requires a specific bursting head to connect to the product pipe and then to the static pipe bursting tooling. Nothing additional is required. Subsequent sections of the restrained joint pipe are assembled during the bursting process as the pipe string progresses.
Sectional pipe with non-restrained joints, however, requires a little different approach. Because the joints are not restrained, something needs to hold push them together and then hold the assembled pipe sections in compression as they are installed. Quicklock style bursting rods and a specially designed cylinder pack provide the solution. The bursting rods are connected from the back end of the bursting head and extend through each section of the sectional pipe. As a new section of pipe is added to the pipe string, the cylinder pack and pressure plate, connected to the column of bursting rods, push the pipe joints together. The pressure plate and cylinder pack then hold the string of assembled pipe sections together, in compression, while the bursting head is pulled forward through the old pipe. Once that section of pipe is installed, the bursting process stops, the cylinder pack and pressure plate are withdrawn and the process repeats.
Product Pipe & Bursting Considerations
Caution should be exercised to ensure that the intended burst length is attainable. Soil investigation should reveal how well the existing trench conditions will react to the compressive/expansive forces of the pipe bursting action. A local geo-technical consultant should be part of the project design and planning, as soil types vary dramatically from region to region, sometimes block to block. If the soil demonstrates that it maintain an annulus for a period of time, the segmented pipe will probably work well. In free-flowing sand and other similar conditions, segmented pipe may be problematic. And a fusion welded pipe system should probably be used instead.
The bursting head is fracturing or splitting the existing pipe, then expanding the broken pipe fragments in to the surrounding backfill. Meanwhile the pipe bursting head is creating an annular space large enough for passage of the new pipe. This temporary annular space must also accommodate the added dimension of segmented pipe bell joints. This may be problematic in some situations.
Common Pipe Materials Main Lines, Pressure Pipe and Non-Pressure Pipe
- Fusion Welded HDPE AWWA C-906
- Fusion Welded PVC AWWA C-900 & C-905
- Restrained Joint Ductile Iron Pipe AWWA C-150
- Non-Restrained Joint Ductile Iron Pipe AWWA C-150
- VCP “NO- DIG” Jacking Pipe
- Restrained Joint PVC pipe AWWA C-900 and C-905; Conduit
Service Line and Lateral Pipe Materials
- Fusion Welded HDPE
- Cast Iron No Hub Soil Pipe
- Cast Iron Bell & Spigot Soil Pipe
HDPE for Sewer and Water, MDPE for Natural Gas
The industry is very knowledgeable about this pipe material and pipe bursting installations. Fusion welded joints help to make this type of pipe into a one-piece pipe section to whatever length is required for a pipe bursting reach. For example, a section to be replaced is 500 feet long; a string of PE pipe will be welded together into a string slightly longer than 500 feet and will be laid down in alignment with the launching pit. This method represents at least 95% of all pipe bursting installations. This procedure always requires adequate lay-down area. Fusion welding this type of pipe during the pipe bursting process is time-consuming and generally performed in the field. Because of years of field experience a number of ways to connect PE pipe to the pipe bursting tooling have been developed. They are generally all reliable with various advantages to the methods. Both pneumatic and static pipe bursting systems can be used for this type of pipe.
Fusion Welded PVC
The water and sewer industry are just beginning to see this relatively new type of PVC pipe. It is butt fusion welded, similar to PE, and offers a PVC pipe that is suitable for many pipe bursting applications. Although the pipe is somewhat stiffer, thus requiring longer launching pits. 5:1 ratio (Length to Depth), the fusion procedures for welding this type of pipe must be adhered to very precisely. Experience has shown that the typical scratching on the outside diameter (OD) of the pipe is within the manufacturers allowances. Because the pipe is stiffer than HDPE for example, it must be installed with a static pipe bursting system so as not fracture the pipe’s connection to the pipe bursting tooling. This type of pipe cannot withstand the heavy hammering action of a pneumatic pipe bursting system.
Restrained Joint Ductile Iron Pipe
This is another new application for a type of pipe that has been on the scene for a very long time. The bell and spigot restrained joint configuration requires that the pipe be pulled backwards (spigot end first). This allows each consecutive bell joint to act like an additional pipe bursting expander. Only a static pipe bursting system should be used for this type of pipe. The pipe is assembled one joint at a time in the launching pit and pulled one joint at a time. The joints are made up quite quickly, usually in just a couple of minutes. In addition, this type of pipe can be pre-assembled into long pipe strings similar to HDPE or Fusion Welded PVC
The advantage of the cartridge loading approach is there is no need for a pipe staging area. This is an ideal solution for urban street conditions. The new replacement pipe can be unloaded, as needed, from a truck and at the end of the day there is no pipe left on site. This process requires the pipe bursting system to start and stop repeatedly. Each joint is made-up in the launch pit, pulled in and then the stopped while the next section of pipe is lowered into the launch pit and assembled to the previous joint.
Loose polyethylene encasement of the ductile iron pipe is not done, as the wrap will be severely damaged by the old pipes fragments during the installation. A pushing cylinder may be used to help the column forward during difficult bursting operations.
Restrained Joint DIP, like all pipes with bell joints, presents a unique challenge in pipe bursting. The bell joint is larger than the outside diameter of the pipe barrel. Thus each bell joint will act as an additional pipe bursting expander. This works very well in soils that do not collapse immediately during the bursting process. Fusion welded HDPE pipes provide a seamless restrained joint pipeline with no projection for the joints. Jointed or segmented pipe materials usually have some sort of bell joint for joining pipe sections together. These bell joints may cause some extra difficulty in pipe bursting where the soils tend to fall back against the new pipe during installation. This may cause significant extra drag for the new pipe string being installed.
Restrained Joint C-900 PVC Pipe
C-900 PVC pipe with a restrained joint utilizes a spline and groove assembly that is very strong. This pipe is assembled and pulled much the same as restrained joint ductile iron pipe. Only static pipe bursting systems should be used due to the stiffness of the pipe. The connection of the PVC pipe to the bursting head consists of an adapter using the pipe and a steel pulling head of the same configuration as the pipe joint. A cartridge loading method can be used. However, this type of pipe appears to be flexible enough to join together before a pipe burst and insert through the launch pit with minimum bending.
Non-Restrained Joint Ductile Iron Pipe
This type of pipe has a very low profile joint and was developed primarily for pipe jacking type installations. When pipe bursting with non-restrained joint pipe the pulling rods are placed through the length of each new pipe section and connected to a restraining or back up clamp that essentially helps to push the column of pipe from the backside. This insures that the non-restrained pipe joints stay in compression thus staying together. The internal lining of the new pipe must be protected from the rods or cable used to pull the pipe. In many situations, the rods are sheathed inside small diameter plastic pipe. This helps prevent any rubbing damage to the lining.
Vitrified Clay Pipe (VCP) with Jacking Type Joints
This particular pipe product is much the same as other non-restrained pipe types. Because this is a clay pipe, special care will be necessary to keep the column in good alignment. These pipe sections come with a layer of compressive material at the joints to help equalize the jacking pressures against the end of each section. Clay pipe is quite heavy s cylinder pack in use along with the static pipe bursting system. This type of pipe is installed using the cartridge loading method.
Welded Steel Pipe
Welded steel is installed by pulling with static pipe bursting systems. The pipe is by definition flexible. So it can be welded together and then pulled in similar to PE pipe. The reality is that this pipe is not really that flexible and probably will need to be welded together as each joint goes in.
While each pipe option needs to be evaluated for appropriateness on a project-by-project basis, the ability to choose between a range of product pipe options has made the static pipe bursting method a more global rehabilitation and replacement solution. The specified pipe and specific pipe bursting equipment should have a proven history similar with the intended application and service environment, as well as data that reflects third-party testing, to substantiate suitability of the pipe by physical property and chemical resistance claims of the manufacturer.
There are other types of restrained joint and non-restrained joint pipe that can be installed with similar methods. Consulting with well-qualified pipe bursting consultants and knowledgeable equipment manufacturers can help to make these applications possible.
TT Technologies, Aurora, Illinois
Public Works, June 2009