Miami Accomplishes Another Deep Diving HDD Project

Fisher Island residents live on one of the most expensive pieces of real estate in the world and rely on a pipeline from the mainland through the Port of Miami for their fresh water supply.  Age, leaks and the deepening of the Port of Miami’s waterway required this important pipeline to be replaced.  

Due to the affluent and fragile nature of Fisher Island and Biscayne Bay, the project required as little digging as possible and the pipe would have to be burrowed deep enough to allow the shipping channel to be dredged. PE 4710, 30-in. diameter high-density polyethylene (HDPE) pipe was used for the 1,600-ft long line that was installed 100 ft deep using horizontal directional drilling (HDD) in August 2011 and came into service in April 2012.

“The main driver for this project was the harbor dredging project that will be done to accommodate the larger Panamax ships that will soon be passing through the new, wider section of the Panama Canal,” stated Tony Radoszewski, executive director of the Plastics Pipe Institute, Inc. (PPI). “The Port of Miami will be one of the few on the East Coast that will be able to do this and be the closest deep water port to Panama in the United States.” PPI is the major trade association representing all segments of the plastic pipe industry.
Post-Panamax ships are too large to travel through the current Panama Canal. Scheduled to be completed in 2014, a new lock is under construction to allow passage of these larger ships that can carry 13,000 containers compared to the ships, which can now hold 5,000 containers. The dredging will increase the water level of the Government Cut and Fisherman’s Channels another 50 ft.

In a news release, Miami-Dade County Mayor Carlos A. Gimenez said, “Port Miami will be one of the only three U. S. Atlantic ports to be at the required minus 50-ft level in time to welcome the new generation of larger container cargo vessels arriving via the expanded Panama Canal.”  

Once the dredging is completed the estimates predict that the Port will grow jobs by 3 percent a year and double cargo traffic in 10 years. Currently the Port of Miami supports 176,000 jobs and $17 billion in annual commerce.  

Big Ships, Deep Dredge, Tough Pipe

The 25-year-old original 20-in. ductile iron pipeline under Fisherman’s and Government Cut Channels was installed using cut-and-cover, buried from 5 to 20 ft below the floor of the channel. This line brings treated water from the mainland and had to be replaced to allow for the Miami Harbor Dredging Program — the Deep Dredge — that will deepen and widen both channels.

“This work — the new pipeline and the dredging — must be completed before the expanded Panama Canal opens,” reported Radoszewski. “And required the Miami-Dade Water and Sewer Department to embark upon a very aggressive timeline…fewer than six months. Using design-build, the department and its contractors were able to complete the new potable water pipeline on schedule.”  

The Miami-Dade Water and Sewer Department (MDWASD) operates and maintains the largest water and sewer utility in the southeast and is the eight largest water utility in United States. The department provides drinking water to more than 2 million customers.  It has more than 7,000 miles of pipeline, 124,000 valves and more than 38,000 fire hydrants.  

“We felt that using HDD with HDPE pipe that exceeded specification would speed the project,” stated Ralph Terrero, MDWASD assistant director water.  “Unlike when the original ductile iron line was installed, we now had the benefit of the latest HDD equipment and pipe technology working for us. We were able to drill and pull the pipe under the channels. Plus, we were able to save time because deep vertical shafts were not needed due to the relative flexibility of the HDPE pipe, just small entrance and exit pits.  This also helped to satisfy residents who did not want to see their land dug up with trenches.”

According to Shajan Joykutty, P.E. senior associate with Hazen and Sawyer, the design consulting firm for the project, “The most difficult part of that job the contractors encountered was creating the pilot hole for the HDD, a very time-consuming and difficult task. The calcareous soil in Miami Dade County is known to be difficult to drill through, and so the procedures and the equipment they used for pilot drilling had to be carefully selected and in some cases it put stress on the drill rods, and that was one of the biggest challenges.  

“The other interesting aspect of this type of project is that as these lines get longer in length. This is a total of more than 1,600 lf. The pulling stresses get to be extremely high at that length on a horizontal directional drill such as this, and particularly at that depth and with that alignment. An installation like this is tremendous in terms of stretch. There are very few plastic pipes that can be installed HDD in these types of installations primarily due to the elongation and stress on the pipe. Steel pipe is too rigid to follow the steep profile that this pipeline needed. Fusible PVC might have been an option but in this particular case the alignment was waist deep so there was a concern about brittle failures.  The design criteria called for using HDPE pipe as the material for the project, so HDPE was the way to go.”  

The 30-in. IPS DR 11 PE 4710 pipe was manufactured by JM Eagle, Los Angeles, and supplied to the jobsite by ISCO Industries, Louisville, Ky.  

The new HDPE pipeline was fused in one segment that was 1,650 ft long with 758 ft under the channel floor. A McElroy MegaMc 1236 unit was used to heat fuse the 50-ft sections of pipe into a single, leak-proof pipeline. ISCO, JM Eagle and McElroy are member companies of the PPI.  

PE 4710 allows water companies to use higher pressures for the same DR pipes or to obtain greater flow capacity for the same pressure rating with higher DR (thinner wall) pipes.  Water main pressure in Miami is from 60 to 80 psi. Compared to conventional PE materials, PE 4710 provides a more cost-effective pipe system due to its improved properties.  

According to PPI, pipe material designation codes continue to evolve as newer and better materials are developed. The latest development in PE pipe resin classification is PE 4710. Because PE resins that qualify for the PE 4710 designation are high-performance materials, they offer an excellent level of performance. This provides the ability to use a thinner walled pipe and still meet the same pressure specifications with increased flow capacities and without compromising safety or long-term service.

Along with the pipe, ISCO provided technical and fusion assistance on the project. According to Bryan Fletcher, ISCO sales manager for Florida, “With PE 4710 material, the safe pull strength is 310,000 lbs, which is about 40 percent of yield. For PE 3608 pipe, that would have been 266,000 lbs. The additional pull strength and the use of PE 4710 pipe was requested due to the complexity of the shot, and the lack of area to assemble the 1,600-ft long pipe added a lot more stress while pull back was taking place.”

The entry angle was 15 degrees.  A Prime Drilling rig provided 1.3 million lbs of pull back on a 6-5/8-in. drill pipe. Additional pull strength was needed as an additional factor of safety due to the continuous curvature of the borehole, which added tensile load to the total pullback force. Pullback duration was about 11 hours.  A Tulsa Rig Iron Inc. MCS 750 system was used for mixing, cleaning and recycling.  

There were also positive environmental aspects to the method of going deep and underground.  

“Being able to complete this project with absolutely zero disturbance to the bay bottom was an environmental victory, one that would not have been possible without HDPE pipe and the HDD technology,” stated Luis Aguiar, Chief Miami-Dade Water and Sewer Dept., Water Distribution. “The fact that we did not disturb the sea grass that is on the bottom of the bay got kudos from the environmentalists. All the environmental organizations were extremely happy.”

The new water line project was on time and under budget. “With the savings, we were able to purchase and install two bidirectional meters on each corner of the Port of Miami to measure the flow of water going in and going out,” Aguiar said. “Before, we didn’t have any means of measuring how much water was being used by the Port. The Port had individual meters for each warehouse, every terminal and every building. Now, by putting in the two bidirectional meters all we have to do is measure those meters and we have the Port usage. There are only two meters to read, not hundreds, which helps us with our efficiencies and further adds to our bottom line.”

“This new pipeline and the new Panamax ships are benchmarks of the future,” said Radoszewski. “We have just seen how successful Miami was earlier this year using a 20-in. diameter HDPE pipeline installed with HDD to replace a 12-in. deteriorated cast iron transmission line at the Rickenbacker Bridge just north of this project. The MDWASD is continuing to lead the way in serving its customers with reliable pipelines, and through its use of leading-edge technology in its on-going program of replacing water lines by using HDD and HDPE pipe.

“This project certainly was a challenge in many respects,” he continued.  “And the obstacles were overcome with a resounding success through a combination of design engineering, HDD installation and the HDPE pipe.”

Steve Cooper has been reporting on the water and pipe industries for several decades.