Written by Michael Woodcock

The Parker Sewer & Fire Sub-district, located in beautiful Greenville, South Carolina, needed to repair an aging and undersized sewer system in a sewer basin they call R-16 Jordan Mill. Like many sewer systems in Greenville County, the Jordan Mill system was built in the 1950’s by and for the textile mills that blanketed the area, formally known as the Textile Crescent. After the mills shut down, Local Special Purpose Sub-districts were created to own, operate, and maintain these water and sewer systems. The Jordan Mill sewer system serves hundreds of homes with mostly 6” vitrified clay pipe (VCP), which struggled mightily to keep up with the flows in its current poor condition. 

 

Keith Dunn of Dunn & Associates was tasked with designing a project that would get the Jordan Mill system up to current standards. Initially, the project was designed as an open cut project. However, the open cut bids far exceeded the budget. Consequently, the project was redesigned and re-bid specifying the Pipe Bursting construction method for replacing the existing 6” & 8” VCP pipe with 8” HDPE. Through a combination of research and experience Mr. Dunn had determined that Pipe Bursting would be the most economical way to replace these lines and get the existing 6” pipe to 8”, as the existing system ran through well-developed back yards with landscaping, fences, garages, and storage buildings. Up till now, Pipe Bursting was essentially the only trench-less method with the capability to economically up-size 6” pipe to 8”.

Portland Utilities Construction Company, LLC (PUCC) of Portland, TN was the low bidder and awarded the project to replace 9300 LF of mostly 6” VCP sewer main with 8” HDPE by the Pipe Bursting method. During preparations for Pipe Bursting, Pre-CCTV surveys revealed that many additions to the homes, storage buildings, and garages had been built over or almost over the existing sewer main. Also, some of the existing sewer mains were so shallow that these structures and asphalt/concrete paving were, in essence, sitting almost on top of the existing pipe to be replaced by Pipe Bursting; placing these improvements within the range of the soil and pipe displacement creating by the Pipe Bursting method. In other words, the Pipe Bursting process could damage some of these surface improvements that were so close to the existing pipe.

The Pipe Bursting method would be feasible for approximately 60% of the project. For the other 40%, an alternative construction method would have to be considered. In the end, there would be a total of 3 different trench-less construction method used to complete the Jordan Mill Basin.

Pipe Bursting
The original design intended to take advantage of the many benefits that the Pipe Bursting Method has to offer. The primary benefit desired of the Pipe Bursting Project was the ability to use a trench-less method to up-size from 6” VCP to 8” HDPE. Up till now, Pipe Bursting has generally proven to be the only trench-less method to be able to accomplish an up-size. However, in order to accomplish Pipe Bursting, soil displacement must by definition of the process occur, and even more so when up-sizing. Other benefits of Pipe Bursting over other trench-less construction methods are its ability to overcome broken, egg shaped, and off-set pipe.

For the majority (60%) of the Jordan Mill project the Pipe Bursting method worked as hoped and expected. Unfortunately, there were two scenarios where the soil displacement would or could cause damage to surface improvements. Shallow depth of the existing pipe to be replaced was the primary cause of the problem.

The first scenario was where the existing pipe alignment ran under or almost under the foundation of a structure and the depth of the existing pipe was shallow. The combination of shallow depth and this pipe alignment brought the existing structures into the zone where soil displacement could have an impact on the existing structure.

The second scenario was where the existing pipe alignment ran under an asphalt or concrete drive and the depth of the existing pipe was shallow. Again, the shallow depth of the existing pipe brought the proximity of the existing pipe and the asphalt or concrete improvement close enough together so as soil displacement could cause damage to the improvement.

In each of these two scenarios, it was agreed by all that pipe bursting would not be the right solution. Alternative trench-less methods would have to be found in order to avoid damaging existing structures and surface improvements or the existing pipe would have to be abandoned and a new pipe would have to be installed at a new alignment by open cut. Open cut installation was not desired in these extremely congested and tight backyard easements and would be much more expensive.

Alternative Trench-less Construction Methods Used
As mentioned above, there were two scenarios to consider for these shallow line segments 1) Pipe Alignment Under Structures and 2) Pipe Alignment Under Asphalt or Concrete Paving. The other variable that was involved was the size of the existing pipe. Some of the existing pipe in these scenarios was 6” and still need to be up-sized to 8” and some of the exiting pipe was already 8”. Of course, the trench-less options available to rehabilitate existing sewer pipe and maintain the same size are more plentiful than trench-less options that can up-size existing 6” pipe to the desired 8” pipe are less. As mentioned earlier, up till now Pipe Bursting was the only prevalent method capable of up-sizing pipe. Consequently, two different methods were chosen to rehabilitate or replace the two-different size pipe.

UV Fiberglass CIPP
For the existing sewer pipe line segments that were already 8”, UV Fiberglass CIPP was proposed and eventually accepted. The UV Fiberglass CIPP system would be able to rehabilitate the line without damaging any structures or surface improvements. Approximately 25% of the project or 2500 LF would be rehabilitated using this method. Most of the services connections were excavated and replaced per the project requirements. For any services that were up under porches or even permanent structures, there was the luxury of being able to internally reinstate fully.

Keith Dunn of Dunn & Associates had this to say about the UV Fiberglass CIPP Process
“The district’s experience with CIPP had not been so great in the past so PUCC provided many references and product data information as to a newer technology known as UV Fiberglass CIPP, which utilizes a woven glass fiber. We had never used UV Fiberglass before and were skeptical at first given it is somewhat thinner than traditional CIPP felt liners. However, after PUCC demonstrated the first segment to us, we were sold. The liner material was actually about as smooth as brand new PVC pipe. Another impressive thing about the UV Fiberglass CIPP is that it is actually stronger in every way as compared to traditional felt (liner) cured by water or steam. The UV cure method allows for no ‘cool spots’ or wrinkles to any extent compared to traditional liners, because as the liner is installed and initially ‘blown up’ the liner can be inspected for problems before the light is pulled back through to cure it.”

Close Tolerance Horizontal Direction Drilling (CTHDD) Pipe Replacement
For the existing sewer pipe line segments that were 6” and need to be up-sized to 8” there were not many options to consider. PUCC Superintendent Gary Testa did some outside the box thinking to provide the idea that was eventually used to upsize the exiting 6” VCP pipe to 8” HDPE without displacing soil and damaging structures or surface improvements like asphalt and concrete paving.

Testa, who had been pipe bursting for over 20 years, had ran into a few isolated instances where soil displacement caused by the pipe bursting process had been an issue, but nothing on the scale of what he had discovered on the Jordan Mill project. “Most project don’t have any issues with heave resulting from pipe bursting”, says Testa. “I’m not saying never, but it’s just not that common.” “On this project, heave was an issue on almost ½ the project.”

“We had used a process called ArrowBore recently on another project to install new pipe where there wasn’t an existing pipe”, says Testa. ArrowBore is a trench-less construction method generically known as Close Tolerance Horizontal Directional Drilling (CTHDD) designed to install new sewer pipe on grade by drilling a hole only ¼” more than the new pipe being installed. This “Close Tolerance” keeps the pipe from floating up down in the drilling fluid, therefore eliminating the humps and sags that would result from a traditional directional drill method where the standard operating procedure is to drill a hole 1.5 times larger than the new pipe being installed, which would have been 4” or half the diameter of the 8” pipe. Testa Continues; “We had also used a traditional directional drilling method once before to replace an existing pipe, but I was worried about the dips and sags that might result on this project and the fact that in some instances we didn’t have the extra space to over-ream by 4”or 5”. So basically, I called the ArrowBore guy to see if he thought his process would work on an exiting VCP line. Neither one of us could think of a reason that it wouldn’t work, so we gave it a shot.”

About 15% of the 6” or 1500 LF was upsized to 8” HDPE on the project utilizing the Close Tolerance (HDD) Pipe Replacement method. The method was able to up-size from 6” VCP to 8” HDPE without displacing soil and therefore without damaging structures or asphalt and concrete surface improvements. Eventually, another 7500 LF of Close Tolerance HDD Pipe Replacement was added to the project in other basins to address shallow pipe that was close to structures or under asphalt or pavement where heave from pipe bursting would cause damage.

Conclusion
As everyone knows, the best laid plans of mice and men can go astray. The Jordan Mill Sewer Basin had some serious unforeseen issues that needed to be resolved. However, this was one of those instances where problems really did create opportunities; the opportunity to use an emerging technology like UV Fiberglass CIPP and the opportunity to adapt an exiting technology to a new application, now called Close Tolerance Pipe Replacement. The Jordan Mill Sewer Basin was certainly the opportunity and the necessity to use 3 different trench-less technologies to complete a sewer rehabilitation and replacement project.