HDPE Used to Expand Water System in San Antonio
January 19, 2012How do you fuse together, bore and pull a 36-in. diameter, thick-walled high-density polyethylene (HDPE) pipe string that links 45-ft sections into even longer threads? The answer is simple. Basically, the same way you do for any HDPE pipe system — face it, fuse it, bore it.
That is how crews dealt with installing a new water main system in northwest San Antonio, where one string of HDPE pipe alone ended up being 1,000 ft long. The project required a 20-ft entrance drop and exit rise so that pipe could be pulled under a creek. The water transmission main project here will connect the existing water mains with a recently constructed pump station and to accommodate future demands in the area. San Antonio Water System selected the contractor and method in a bid process based on best price.
“This new water main will connect the gap between the new pump station and the existing main to provide additional capacity for future growth in our city,” explained Juan G. Rodriguez, P. E., project engineer, production and transmission engineering department for San Antonio Water System (SAWS). “It goes through a very rough area that has a lot of rock and ravines — not the easiest terrain to bore through — plus we had to deal with an active creek. The HDPE pipe is tough and provides the type of deflection you need for directional drilling and has the best cost-effectiveness.”
“This was a very challenging installation, but perfect for HDPE pipe,” observed Tony Radoszewski, executive director of the Plastics Pipe Institute Inc. (PPI), a non-profit, manufacturing-based trade association dedicated to expanding awareness about economics, performance benefits and environmental advantages of plastic pipe systems. “And it’s not a typical horizontal directional drilling (HDD) HDPE pipe project because SAWS elected to use very thick walled pipe — greater than 4 in. in thickness — in a larger diameter size to meet its design specifications. But, even at this extreme, the HDPE pipe installs easily and delivers a highly sustainable, completely leak-free system with fused joints. And these characteristics are the norm when using HDPE pipe.”
Pressure class for the system is 200 psi, which provides enough power for the distance between pumping stations, the area’s elevation and the number of projected customers. “This pressure zone is located on those higher elevation areas in San Antonio’s hill country so the water has to travel up as well as far,” Rodriguez said.
The project required more than 1,900 lf of HDPE pipe. Manufactured by Performance Pipe, a division of Chevron Phillips Chemical Co. LLC, in Plano, Texas, and a PPI member company, the pipe is DriscoPlex 4000/4100 36-in. DIPS DR9 PE 3408 with a 4.62-in. wall thickness.
The project included three HDD pulls. “They were labeled Line A, B and D,” said Bob Gajeske Jr., whose company, Gajeske Inc. (Grand Prairie, Texas), supplied the pipe and also did the fusion. “Line B is the longest pull … It was almost 1,000 ft long alone; but we didn’t experience any problems fusing the pipe. We just had one operator on a fusion machine, a McElroy 1600, with a four-jaw clamp and hydraulic lift. That 65-in. unit had absolutely no trouble clamping, facing or fusing that pipe at all — it worked just as easily as when we fuse HDPE pipe in smaller diameters with thinner walls.”
McElroy is an equipment manufacturer located in Tulsa, Okla., also a PPI member, and provided the pipe stands to hold and align the pipe which had self-contained gasoline engines that power the lift. A trackhoe was used to load the pipe sections into the fusing machine and onto the pipe stands and to pull the pipe.
“These hydraulic pipe stands really helped with the process,” Gajeske continued. “They enabled us to quickly and easily maneuver the pipe back and forth, up and down, in order to get a good alignment in the fusion machine. That really sped job progress. Initially it was projected that the pipe was going to take about 27 days for us to fuse all of it. We ended up doing it in 14 days. Not much was different from fusing smaller, thinner wall HDPE pipe. We just had to crank the pressures up. Things went really quickly and smoothly.”
Imperative to the success of the project was the ability to utilize the HDD installation method for specific areas. “It was essential that we directionally drilled to circumvent that creek,” said Rodriguez. “We saw it as the only option. We couldn’t dig a trench due to the steep terrain and you can’t have the water main exposed, especially on these types of creeks in Texas, which are known for flooding and washout conditions. So we had to go under the surface, which required going down more than 20 ft, then horizontally under the creek. We did the same for the other areas that were just ravines.”
The directional bore and pull was done by Cherokee Directional Drilling of Longview, Texas. “This job was not unlike any other job in most ways,” stated Kerry Holden, president and the onsite project manager. “But, because we needed to oversize the hole — it was more like a tunnel when we got done — up to 48 in. We first had to go in and shoot a pilot hole, then do the rest in phases. After the pilot, we drilled 8-in., 24-in. then the 48-in. It took about three and a half weeks to do the largest one, which was nearly 1,000 ft. Once we got the hole cut through, however, it took just a few hours to do the pull.”
The Cherokee crew used a self-contained Vermeer Navigator D330x500 horizontal directional drilling System with 330,000 lbs of pullback.
For the three lines that were pulled, Line A was 360 ft; Line B was 970 ft and went under the creek; and Line D was a 565-ft pull, down, under and up a 60-ft deep ravine.
“HDPE pipe was the product of choice for the job because of its ability to perform under all the particular circumstances we were dealing with here and because it could be directionally drilled,” stated Rodriguez.
“Just the numbers alone on this job are staggering,” said Radoszewski. “Thick-walled pipe fused for nearly 2,000 ft in 14 days — then, add in the conditions, like being able to circumvent an active creek and defeat deep ravines using horizontal directional drilling — these make this project remarkable and the team can be very proud of their successful accomplishments. Plus, using HDPE pipe in the most sensitive areas where failure simply isn’t an option is a testament to the product. Despite all the difficult details, the crews felt this was just another HDPE job. And that I find to be the greatest attribute about this project, and directly tied to the merits of the pipe material: it’s just another ordinary, dependable performance for HDPE pipe.”
Steve Cooper has been reporting on the water and pipe industries for several decades.