To compare material performance during installation, we used 10-inch HDPE and 8-inch and 10-inch Certa-Flo GreenLine PVC pipe, a restrained-joint PVC pipe for trenchless and pipe-bursting applications. The crews performing the installation preferred the PVC to the HDPE for several reasons, including:
- It takes a three-person crew eight hours to fuse the necessary amount of 10-inch HDPE pipe for an hour of pipe bursting. But the CertaFlo GreenLine doesn't need to be fused. It can be installed as the pipe-bursting machine pulls it into the ground, thanks to its unique spline-locking joint system tha utilizes an integral bell instead of coupling.
- For bursts of less than 6 feet where there's 50 feet or so behind the insertion pit, the restrained-joint PVC pipe can be assembled as fast as the machine can pull. Speed of the burst is hard to estimate because of differences in each project, but the actual installation of the main has been between 2 and 7 feet/minute.
Static pipe bursting not only allows us to replace 6-inch clay mains with 6-inch PVC, it also lets us increase the size of the main by two pipe sizes. We replaced 6-inch clay pipe with 8-inch and 10-inch pipes. Many of the small-diameter mains are currently at a minimum grade for their diameter:
- Minimum recommended grade for 6-inch pipe is .5% or 6 inches/100 feet.
- For 8-inch pipe: .33% or 4 inches/100 feet.
- For10-inchpipe:.25%or3inches/100 feet.
By replacing a 6-inch main that was exceeding its designed capacity at minimum grade with an 8-inch pipe at the same grade, we got a new smooth pipe installed at a grade off of the minimum edge of the recommended slope—and with a significant increase in capacity. This allows us to accommodate past and future growth.FIVE DISTINCT ADVANTAGES
Anybody who can do a traditional open-cut job can learn how to do a pipe-bursting job.
Another big advantage is that disturbance to surrounding areas is minimized. We burst mains under four-lane traffic roads, garages, chain link fences, manicured lawns, creeks, and through thickets of trees and soccer fields without disturbing the surface, except to re-tap services and excavate 20-foot x 5-foot pits at the start and finish points. Also, we didn't have to check the grade of the pipeline with a laser every few feet as required with open-trench projects because the new pipe maintains the grade of the original pipe.
Trenchless methods are safer for the staff, taking less of a physical toll on individuals. Plus, backfill materials and spoils are greatly reduced.
With this technology, we installed 400 feet of PVC in about eight hours. It took five to six workers about 1½ hours to dig pits; 1½ hours to set up equipment and put it back on the truck; two hours to insert rods, attach to pipe, and install; and three hours to connect to each end and backfill pits. Pipe is put together as it is pulled back into the ground, but the required taps and manholes take some additional time.
Finally, if mains are replaced in existing space, easements are not an issue. Increasing capacity by upsizing the main takes care of capacity and grade issues that may have been causing sewer overflows.BUDGET CONSIDERATIONS
We compared costs associated with conventional open-cut methods, and found that pipe bursting is less expensive, in almost all instances, in the long run.