Segmented pipe is assembled one joint at a time in the launch pit. This works well where space available for pipe lay-down is limited. Static bursting procedures for segmented pipe vary depending on whether it has restrained or nonrestrained joints. Segmented pipes with restrained joints require the bursting head to connect to the replacement pipe and then to the bursting tooling. Nothing additional is required. Subsequent sections of the restrained-joint pipe are assembled during the bursting process as the pipe string progresses.
In pipelines where the joints are not restrained, something needs to push the assembled pipe sections together and then hold them in compression while they are installed. Quick-lock bursting rods and a special 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 pipe. As a new section of pipe is added to the 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 hold the 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 Once that section of pipe is installed, the bursting process stops, the cylinder pack and pressure plate are withdrawn, and the process is repeated.OTHER TYPES
Restrained-joint ductile iron pipe's (DIP) bell-and-spigot joint configuration requires that the pipe be pulled spigot end first, so that each consecutive bell joint acts as an additional pipe-bursting expander. Only a static pipe-bursting system should be used for restrained-joint ductile iron pipe. The pipe is assembled in the launching pit and pulled through one joint at a time. The joints are connected quickly, usually in just a couple of minutes. This technique requires no pipe staging area, so it is ideal for urban street conditions. The new replacement pipe can be unloaded from a truck as needed, and at the end of the day no pipe is left onsite.
Restrained-joint C-900 PVC pipe, which uses a very strong spline and groove assembly, is assembled and pulled in much the same way as restrained joint DIP. Due to the pipe's stiffness, only static pipe-bursting systems should be used. The PVC pipe is connected to the bursting head by an adapter with the same configuration as the pipe joint. C-900 PVC pipe segments can be loaded one at a time, but this type often is flexible enough to be joined together before a pipe burst and inserted through the launch pit with minimal bending.
Nonrestrained-joint DIP has a very low profile joint and was developed primarily for pipe-jacking installations. When pipe bursting with nonrestrained-joint pipe, the pulling rods are placed through the length of each new pipe section and connected to a backup clamp that helps push the column of pipe from the backside. This ensures that the nonrestrained pipe joints stay in compression, and thus stay 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 to help prevent rubbing damage to the lining.
Vitrified clay pipe (VCP) with jacking-type joints is similar to other nonrestrained pipe types. As a clay pipe, it requires special care to keep the column in good alignment. 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, so a cylinder pack is used along with the static pipe-bursting system. VCP is installed one segment at a time.
Options need to be evaluated for appropriateness on any given project, but the ability to choose from different products has expanded the practical uses of static pipe bursting. Always specify pipe and pipe-bursting equipment that has a proven history with the intended application and environment.
— Collins Orton is a product specialist with TT Technologies in Aurora, Ill.Web Extra
For a video of a static pipe-bursting project, click here.