HDD Under the Galveston Ship Channel

When Hurricane Ike hit Galveston, Texas, in September 2008, Galveston Island and Pelican Island — the latter a small island located across the Galveston Ship Channel from Galveston Island and home to Texas A&M University at Galveston — experienced a total water system failure. Pelican Island went without clean water for several days. Following the failure, the City of Galveston identified several infrastructure projects to strengthen its water system.

One such project was installing a new waterline from Galveston Island to Pelican Island. Before the storm, Pelican Island was served by a single waterline that dead-ended at Seawolf Parkway, a major street that runs across the island, providing water only from one direction. The aging cast iron pipe also experienced several leaks over the years and was not reliable. Consequently, the City decided to build a new waterline to create a loop that would allow city officials to have a redundant source of water and maintain service to the island in the event of future storms.

The $4.6 million project, funded with federal disaster grants, included 13,800 lf of 20-in. diameter waterline and all associated appurtenances. The waterline starts from the Texas A&M University Campus on Pelican Island, runs along Seawolf Parkway, then goes underneath the Galveston Ship Channel, comes up on Holiday Drive on Galveston Island and finally connects to the University of Texas Medical Branch (UTMB) elevated water tank.

“By looping the system, Pelican Island can be fed from two different directions,” said David VanRiper, director of municipal utilities at the City of Galveston.

Planning and Design

To complete this project, the City in 2010 commissioned Lockwood, Andrews & Newnam Inc. (LAN), a planning, engineering and program management firm headquartered in Houston, as its design engineer. Of the 13,800 lf of waterline, the project team had to install 3,700 lf underneath the Galveston Ship Channel.

After considering various alternatives, the City and LAN decided that horizontal directional drilling (HDD) was the best solution for the portion of the waterline under the ship channel (the rest of the waterline was installed using an open-cut approach).

“We could have built really deep shafts on either side of the ship channel and tunneled underneath using a microtunnel boring machine,” said Jared Barber, P.E., one of LAN’s project engineers on the project. “But that option was expensive and potentially risky if you lose the machine underneath the ship channel. It could also be hand dug, which is how the previous pipe was installed. But that’s also risky from a safety standpoint. With HDD, everything is done from the surface and is, therefore, a better option.”

To perform HDD successfully, LAN had to take in to account a number of design and planning issues. Chief among them was getting a permit from the U.S. Army Corps of Engineers. The Corps had strict permitting requirements that required the waterline to be installed within a 30-ft easement across the channel.

Additionally, the easement’s U-shape meant that the waterline had to be installed on a compound curve — two vertical curves and one horizontal curve — within the easement, unlike a normal directional drill.

“One of the biggest design issues was ensuring that the directional drill would stay within the 30-ft easement, especially since there is a horizontal curve under the ship channel,” said Barber. “Typically, when you are drilling under a ship channel, you curve down, level out and then curve up to the other side. Here, after curving down, we had to take a horizontal right turn before coming up to the other side. We provided strict specifications for the guiding and tracking equipment used for the HDD to ensure that the drill path stayed within the permitted easement.”

Other design issues included crossing underneath an existing marina with steel sheet piles that were 80 ft deep, as well as selecting a corrosion-resistant pipe material that could withstand the island’s brackish water and serve the City for a long time. To satisfy these requirements, the City and LAN decided to install the waterline at a depth of 110 ft below mean sea level. A specially-made high-density polyethylene (HDPE) pipe with a dimension ratio of 7.3, an outside diameter of 28 in. and inside diameter of 20 in. for a 4-in. wall thickness was designed for installation under the ship channel (The team chose PVC for the portion of the pipe outside the ship channel).

LAN reviewed the marina’s as-built drawings to determine the exact location of each pier and selected an alignment that would not impact these piers as the waterline surfaced from underneath the ship channel. To prevent settlement, the drill path was designed with a 150-ft, 36-in. steel casing underneath the marina entrance.

After finalizing the design, the team spent considerable time looking for a manufacturer that could make such a thick custom-designed HDPE pipe. Another issue was finding a contractor that could execute the HDD that deep to the required design specifications. After reviewing several contractors and their bids, the team selected James Construction as the prime contractor and Janco Directional Drilling Co., as the subcontractor for the HDD. JM Eagle manufactured the custom-designed HDPE pipe.

Construction Challenges

As soon as construction got under way on the new waterline, the old line experienced a break, delaying the project.

“When we dug the first floor pit to install the HDPE pipe, the portion of the cast iron pipe that was adjacent to it moved and cracked,” said VanRiper. “We had to find a special contractor to repair 90 ft of the old line. It required an excavation of almost 15 ft and we had people working around the clock for two to three days. Pelican Island went without water for those days.”

Another challenge was preventing the hole from collapsing during the HDD process.

“As the size of the hole increased, the contractor pumped it with a drilling mud made of bentonite,” said Barber. “Based on the soil conditions, the contractor kept varying the viscosity of the drilling mud during construction. To keep the hole open, the crew kept pumping drilling mud 24 hours a day for several days. This led to noise issues near the neighborhood where the drill rig was set up. We implemented a number of sound attenuation measures and coordinated with the neighborhood to ensure there wouldn’t be too much disturbance. It was quite a challenge.”

Noise wasn’t the only public concern. VanRiper says as the waterline surfaced on Galveston Island, the City had to close off a lane at Holiday Drive, a major thoroughfare, which created traffic issues.

“We had complaints about roads being blocked off,” said VanRiper. “We also paved Holiday Drive as part of the project, which inconvenienced the public even more. Also, we had to tie everyone to the new line once it was in place, which meant that we had to shut down UTMB’s water supply for a while. We coordinated with residences, businesses and the UTMB and educated them as the project progressed. They understood that this was a critical waterline and were cooperative.”

Conclusion

Despite these challenges, the City and the project team completed the waterline on time and under budget in January 2013. VanRiper said the new waterline has worked so well that the City decided to take the old cast iron pipe out of service.

“The new waterline now feeds the entire island and we haven’t faced any problems,” said VanRiper. “Using HDPE pipe turned out to be a good decision and we will consider it for future projects as well.”

The City’s proactive approach on this project, along with other infrastructure improvements, has enhanced Pelican’s Island’s resiliency and will hasten the community’s reentry after an evacuation.

Shelley Serres, P.E., is an associate and senior project manager at Lockwood, Andrews & Newnam Inc.