The 2010 Trenchless Technology Project of the Year for New Installation brought together everything that is exciting about a challenging project: teamwork, tough subsurface conditions, challenging logistics and drilling under water over a great distance that sets a new standard for pipe performance.
All of these elements successfully converged in New Jersey in spring 2010, resulting in a 5,365-ft HDD project that brought customers of the Middlesex Water Co. a new 24-in. fusible PVC water main that was able to be installed quickly, efficiently and perhaps, more importantly, cost-effectively. Project officials also note that this project set a world-record for distance using 24-in. FPVC.
The project took place in a largely urban area in central New Jersey in Perth Amboy and Sayreville. An overwhelming majority of the project (some 4,800 ft) took place under the Raritan River and adjacent marshland, which necessitated some fancy maneuvering on the part of the drilling contractor, designer, as well as the pipe supplier to find enough space to layout the host pipe.
Construction setup began in early March but the project planning and design took place months in advance so by the time drilling was to commence, contingency plans for every aspect of the project had been drawn up — including switching to using the HDD intersect method, if needed (it wasn’t).
“There was a tremendous amount of teamwork between all of the parties,” said David Tanzi, P.E., BCEE, associate and senior project manager with CDM. “We had a built-in team approach during the construction phase.”
CDM served as the design engineering firm for the project, with Northeast Remsco Construction Inc. serving as the general contractor and Mears Group as the HDD subcontractor. Underground Solutions Inc. supplied the FPVC pipe and was also responsible for the pipe fusing operations.
Middlesex Water Co. (MWC) is a 113-year-old, NASDAQ-listed company providing water, wastewater and related utility services to a population of nearly 400,000 in central New Jersey and Delaware. The problem the utility faced was what to do about a 104-year-old cast-iron water main that connected Perth Amboy and Sayreville by way of the Raritan River — the main had been through various forms of rehabilitation over the years and MWC officials were looking for a permanent solution to its continued deterioration.
“The existing main had experienced numerous breaks over the past two decades due to age, corrosivity and the unstable nature of the under water environment,” said G. Christian Andreasen, P.E., MWC director of engineering.
MWC had tried numerous solutions over the last 20 years, including sliplining a portion of the line under the river with HPDE, as well as cleaning and cement lining a portion of the main to extend its useful life. But outages caused major operation disruptions and repairs were occurring with increasing frequency.
“You get to the point where you say, ‘Even though we know it’s going to be a difficult and costly replacement project, we can’t keep making these untimely repairs, spending upward of hundred thousand dollars each time, usually under emergency situations,’” Andreasen said.
So the decision was made to replace the line — but next came the challenge of what method of replacement and type of host pipe would be the most efficient and cost-effective. Various construction methods were discussed, including pipe jacking, open-cut, microtunneling, conventional tunneling and HDD. After an extensive evaluation phase, HDD was selected based on the project conditions, as well as its cost-effectiveness.
A similar process was done to select what product pipe to replace the existing main. “Based on what we had set for the vertical profile, the subsurface conditions and overall cost, FPVC pipe became the frontrunner for the pipe material,” Tanzi said.
FPVC pipe has started to make its presence known in the HDD market over the last few years, as more contractors accept its use in HDD. But selecting FPVC made this a risky project on several fronts, most notably, this diameter of FPVC for this bore length had never been done before, which upped the ante. It also created a challenge for the contractors in terms of performing the pullback, which is typically done in one non-stop pull — which was not possible on this project.
“Ideally, when you are pulling back the final product, you like to do it in one continuous pull,” Tanzi said. “Because of the urban area we were in, we didn’t have room to string out close to 5,400 ft of pipe, so multiple sections of pipe had to be fused together during drilling. We would have to stop pulling back for up to three hours while the intermediate fuses were being done.”
One key to the success of this challenging project was the geotechnical analysis performed by CDM during the design phase. Geotechnical studies are standard on projects but Tanzi noted that MWC went beyond the routine soil review to make sure all parties knew exactly what ground conditions were involved. The investigation conducted consisted of eight marine borings and three land borings, totaling 780 ft.
“Assessment of the data indicated that the HDD installation could be high risk, given that the soft materials could cause problems maintaining the borehole course and fluid circulation, while the hard materials would be difficult to penetrate,” Tanzi said. “[The extensive geotechnical investigation] helped to set the vertical profile of the pipeline and we were able to pinpoint where the bedrock was on the north side of the project and where it wasn’t on the south side. Our goal was to set the vertical alignment just above the layer of bedrock.”
“The geotechnical report was key. The soils were very tricky to deal with,” said Greg Bosch, Mears Group project manager. “We went through a very hard section and stayed just above the bedrock during drilling and transitioned to very soft material.”
Time to Drill
Mears used two American Augers drilling rigs for the project, which called for drilling the pilot hole north to south, exiting on the Sayreville side of the river. A 140,000-lb rig was set up on the north side of the river to drill the 10-in. pilot hole. The 880,000-lb rig was set up on the south side of the river and would handle reaming and pullback operations. Two Tulsa mud systems (a 750-gpm mud system and a 1,000-gpm mud system) and a Tulsa Triplex pump were also stationed on the site.
Before drilling the pilot hole, Mears crews needed to install 140 lf of 42-in. steel conductor casing at the entry due to the proximity at the river’s edge and the shallow depth of cover. Mears installed the casing through rubble and concrete debris in order to stabilize the start of the pilot hole. Once completed, the casing was cleared and centralizers were installed to initiate pilot hole drilling.
“We used the casing to get through a lot of the concrete and rubble fill that was used to build the banks along the river and to get into the clays where we could do the steering a lot better and minimize inadvertent returns along the banks,” Bosch said.
Crews began drilling the pilot hole on March 11, finishing it on March 31. Mears used a SlimDril International Drillguide GST (gyro) system (with the assistance of SlimDril International personnel onsite) for the first portion of the hole — approximately 700 ft — due to the presence of ferrous debris along the river’s edge. “There was a lot of material in the river bottom to be concerned with,” Bosch explained. “Magnetic interference throws off the survey readings.”
After the crew drilled through the initial 700 ft, they switched from the Drillguide GST System to its Para-Track II wireline system that also was equipped with a pressure probe. “We had to be cognizant of the drilling pressures and monitor the annular pressure to minimize any inadvertent returns escaping into the river,” Bosch said.
The final exit location of the pilot hole was within 5 ft of the target hole. The advance rate for drilling ranged from a low of 22 ft per day to a high of 1,319 ft per day.
Reaming took place between April 6 and April 26. When it came time to ream the hole, the team of CDM, Mears and Northeast Remsco decided to ream the pass using 26- and 36-in. reamers. But instead of doing two separate reaming passes, they instead would be done in tandem, necessitating just one pass through the hole. The advance rate for reaming ranged from a low of 62 ft per day to a high of 589 ft per day.
“We had a pre-reaming meeting and discussed whether to do the reaming in one or two passes,” Tanzi said. “The team decided to ream in tandem, giving that subsurface conditions were soft and to minimize the number of times we went in and out of the hole. There was less risk involved in this option.”
One of the project’s biggest challenges was finding a staging area large enough to handle the 5,365 ft of FPVC. CDM reviewed options on the south side of the river, but the mix of residential and commercial properties nixed that option. On the north side in proximity to the drilling operations was an old, abandoned site and MWC and CDM were able to secure a temporary easement to lay out the FPVC pipe.
The pipe staging area limited pipe strings to be fabricated up to a minimum of 1,500 ft, requiring four pipe strings and three tie-in fusion welds by UGSI during pullback operations. To reach the borehole from the pipe staging area, the FPVC pipe was suspended over a major roadway and supported on rollers as it traversed a steep hillside with numerous elevation changes.
Pullback went smoothly, taking approximately 23 hours. In order to minimize pullback forces, the pipe had to be filled with water during the entire pullback process. Ballasting the host pipe with water began about half way during pullback of the first pipe string, needing approximately 665 gals of water for each string of pipe.
Northeast Remsco handled the hydrostatic testing of the pipe, as well as making the proper pipe connections on both sides of the river to place the new pipe into service, meeting the Memorial Day holiday deadline, the beginning of the MWC’s peak water demand period for summer.
“Prudent investment in our infrastructure is key to our ability to continue delivering high quality utility services,” said Andreasen. “We thank the talented teams who helped to deliver this project on time and on budget.”
Sharon M. Bueno is managing editor of Trenchless Technology.