Contractor Defeats Tough Soils to install NG Pipeline in the Lone Star State
With several large natural gas transmission pipeline projects underway, industry leading pipeline construction contractor Pumpco, Inc. from Giddings in Texas has been busy installing gas pipeline throughout the United States. The multi-facetted pipe contractor is well versed in a wide range of pipeline installation methods. On a recent section of pipe in Southern Texas, near Big Bend State Park, the contractor employed dynamic pipe ramming to install a section of Ø 1.070 mm (42“) pipe under a roadway, through extremely difficult soils.
The 65 meter ramming project was part of a larger natural gas pipeline installation. This particular section of 42-inch steel product pipe proved to be very challenging. To install the pipe, Pumpco crews used a 800 mm diameter GrundoramApollo
pneumatic pipe rammer.
Rick Melvin, pipe ramming specialist with TRACTO-TECHNIK’S US sister company TT Technologies said, “This project was full of challenges, but the crew know what they’re doing with their modified pipe ramming version of slick bore. Plus, having the most powerful pipe rammer in the world on the job, helped as well.”
During the slick-bore process the product pipe is welded to the back end of an installed bore pipe. A winch is connected to the lead end of the bore pipe and is used to pull the casing out. As the bore pipe is removed the product pipe is pulled into place. In this scenario, the bore pipe is installed with a pneumatic pipe rammer. Once the product pipe is installed, the bore pipe can be used again for the next slick-bore. The bore pipe does all the difficult work and allows the product pipe to be installed as stress free as possible.
On The Job
Pumpco crews began by digging a 50 m trench leading up to the crossing to accommodate the new product pipe on the north side of the road. An oversized trench was completed on the south side of the road to facilitate pipe ramming operations. Once prep work was complete, crews welded a cutting shoe on the lead end of the first section of the dummy pipe.
Melvin said, “The cutting shoe really strengthens the leading edge of the pipe for maximum penetration through difficult soil and rocks. Because of its oversized cut, the shoe reduces both external and internal friction on the pipe. The cutting shoe also helps protect the pipe’s coating or insulation. Now on the Pumpco project, they were not able to utilize bentonite, but in other configurations the cutting shoes also create a channel for the flow of a bentonite/polymer mixture. Their conical internal surface reduces soil displacement and influences the bore’s accuracy.”
Ramming proceeded without incident for several casing sections until progress slowed dramatically. Pumpco Project Manager Hunter Hill said, “The entire crossing was approximately 65 m from entry to exist. We made it 45 m and ran into, what I’d describe as, a naturally occurring coble concrete that completely halted the progress. We advanced 1 m one day and then maybe 30 cm the next day. So we decided to stop, figuring that the pipe might actually be collapsing, and try to dig it up and see what we encountered.“
“We had to use a hammer hoe to break through the material and expose the pipe in the easement. If we didn’t have that big hammer, we wouldn’t have made it to the other side, we would have been stuck under the road.” Once the pipe was free, Pumpco crews rammed another section of bore pipe in and cut off the now deformed cutting shoe. After backfilling back to the road, crews began cleaning out the casing.
HDD rig used for pipe cleaning
Pumpco Project Manager Hunter Hill said, “We used an HDD rig to clean the spoil out of the carrier pipe. First we used a mud motor, going in and out for the first 6 m or so. Then we ran some cross over subs and used a 24-inch (Ø 610 mm) rock motor backwards to clean out the rest. We yo-yoed through it pulling out a little bit at a time until we only had a little bit of debris in the bottom. Then we pushed a pig through the pipe and that squeegeed it right out.”
After the spoil was clear, crews welded the new product pipe to the end of the installed casing and then moved the Grundoram to the north side of the road. There, crews welded a small section of 500 wall casing, a sacrificial pipe, to the back of the product pipe to facilitate the rammer. With the spoil cleaned from the bore pipe, crews were able to ram the product pipe in slowly without incident. Pumpco crews simply cradled the product pipe during the process with side booms and straps until it was completely installed. Once the installation was complete, Hill’s crew removed the bore pipe and the sacrificial pipe section and turned the project over to another Pumpco division to continue tying the line into the rest of the pipeline. The entire project took two weeks for set up and one week for ramming and welding.