Much in the same way as Europe’s narrow streets, historic structures and aging infrastructure led to the rise of trenchless technologies like pipe bursting and horizontal boring, the long stretches of installed underground transmission lines has led to the development of new trenchless techniques, namely pipe extraction. The pipe extraction process is used to remove pipelines from the ground utilizing some of the same trenchless technology that is used to install them.
A project near Baytown, TX, highlights the need for this process. HDD contractor Directional Service South, LLC., Bossier City, LA, was selected to extract a series of existing pipelines that ran under the shipping channel at Cedar Bayou. The Cedar Bayou channel facilitates barge traffic from an intersection with the Houston Ship Channel to several miles upstream.
Jake Gautreaux, founder and co-owner of Directional Service South explained, “The channel is being expanded, I assume to accommodate bigger ships, the bigger loads, the bigger barges, etc. We were contracted to extract the ship channel crossings, but first we needed to install new lines, deeper, in order to allow the channel to be expanded.”
While the new lines would be drilled in place, the extraction of the existing lines would necessitate an orchestrated effort that included the use of pulling blocks, pulling equipment and pneumatic pipe rammers.
Gautreaux has several decades of HDD experience and started Directional Service South in 2005. He began his career in high school and college doing HDD work for an established contractor and later saw the opportunity in pipeline work. Directional Service South employs 35 to 40 people year round. In recent years the contractor has become particularly adept at mainline pipe extraction, which is becoming more common as underground infrastructure ages and above ground infrastructure changes.
According to pipe ramming specialist Rick Melvin from trenchless equipment manufacturer TT Technologies, Aurora, Ill., pipe extraction is an evolution of existing ramming techniques. He said, “Using pipe rammers on HDD projects is nothing new in the industry. It’s very common now to see a pipe rammer on an HDD jobsite for a variety of reasons. TT Technologies and it’s vendor partners have worked together to develop the HDD Assist techniques over the last 30 years. Pipe extraction is one of those methods.”
The extraction project at Cedar Bayou would require two rammers and a significant amount of pipe extraction knowledge and skill.
Pipe Extraction Preparation
Before the project even begins, making sure the equipment is ready to go is the first important step. Gautreaux said, “We take a lot of pride in cleaning and conditioning everything from shackles to cables to the hammers, breaking them apart, cleaning them up, putting them back together the right way, making sure everything’s just the way it needs to be. So that way, whenever you do need to take it, it’s ready to go, 100 percent. There’s no question. Probably the stuff that you do when you’re not on the project is just as important as when you’re on the project. Another key element is just a good plan. Designing a plan that can be followed and executed successfully.”
The first portion of the Cedar Bayou project involved replacing the pipeline sections that were soon to be extracted. Prior to extracting the existing lines, Directional Service South crews had to go in and install new lines, deeper under the channel. The new pipelines ranged in depth from 40 to 80 feet underneath the bottom of the bayou. This provided enough clearance for the expansion of the channel. Gautreaux said “We did not have any issues with that; it went like gangbusters. The general contractor came back in and tied the lines in. It took them about another month to get everything cleaned and reconnected to the existing mains. And then we came back in to extract the abandoned lines.”
Directional Service South needed to extract a range of pipe diameters including a 30-inch, a 12-inch, (2) 8-inch diameter pipes and (3) 6-inch diameter pipes. All of them averaged between 1,300 and 1,500 feet in length. At first, crews hoped to only extract the section of each pipe that ran immediately under the channel. However, that option was not attenable.
Gautreaux said, “Initially we were going to go to the water’s edge on both sides so that the extraction would be shorter. Shorter and therefore simpler, but the state of the ground conditions and the marsh, combined with the rising tide and the north wind blowing in at the same time, proved to be too difficult. It kept pushing us back to where we had originally installed the new ones. So that’s the location where we decided to perform the extractions.”
Pipe Extraction Action
The general contractor built a ring levee to allow for as much space as possible on the jobsite. Gautreaux explained, “The levee was built, obviously, to hold back that water. As a tide would come up, we’d be underwater. The general contractor went through there and just pushed up the top foot of dirt into piles. They just kept pushing it out until the levy encompassed the job site.” A 300- by 80-foot timber platform area on the extraction side of the channel was then established to work from.
The extraction equipment configuration often varies depending on the specific jobsite conditions. Melvin said, “Pipe extraction is really a combination of forces being exerted in the pipe in order to free it from the ground and remove. You have pull force and push force. You have percussive and static forces working together. The percussive force is supplied by the pneumatic pipe ramming, sometimes two. And the static force through a drill rig or dozer or some other vehicle pulling. And often you need some kind of force multiplier that helps you achieve the kind of controlled force levels that you wouldn’t otherwise be able to achieve. In this case a 9-part, 500-ton block system.”
For the project at Cedar Bayou, the 30-inch cement coated pipeline was the first to be extracted. The equipment configuration on the extraction side included a 24-inch Grundoram Taurus pneumatic pipe rammer connected to the lead end of the pipe through a fabricated extraction sleeve to provide a pulling percussive force. The static pulling force was applied to the rammer through a cable that ran through the 500-ton block system. The actual static pull force was applied by a track-hoe. Another 24-inch diameter Grundoram pipe rammer was connected to the rear of the pipeline to supply a percussive push force. Two 1600 CFM compressors were used on the project, one for each pipe rammer.
Melvin said, “The pipe rammers not only provide push and pull forces, they actual help in re-energizing the drill fluid that surrounds the pipe underground. That’s key. Once that fluid is active again, the static forces can be applied and begin to move the pipe more easily.”
Once set up was complete, Directional Service South crews were able to begin extraction. Gautreaux said, “So the pulling blocks were set. We could pull about 80 feet out at a time with the blocks and cut off the pipe. After we pulled probably three to four sets, we were able to bypass the blocks altogether and pull it out with a couple track-hoes, just walk it out. We would leave the hammer run and then once we ran out of air hose, we’d be at 50 feet or so. We would cut the pipe, put the hammer on, pull it again until it got easy enough to just pull with the track-hoe.”
Pipe Extraction Reaction
It took crews six days to extract the 30-inch pipeline and move onto the next. The first of two 8-inch lines was extracted next. The first one took four days to remove, while the second 8-inch diameter line took just two days. Next, Directional Service South crews focused on a series of 6-inch diameter pipelines. The first one was successfully extracted after three days. The next two took one day each to remove. Finally crews moved on to a 12-inch diameter pipeline, extracting it over a three day period.
According to Gautreaux there is a science to the extraction process when it comes to the pipe rammers. He said, “Making sure to operate the hammers in the most efficient way, is really important. They can’t be run wide open, but they can’t be operated at a point where it’s not enough, if that makes sense. You need to keep the swimming motion out of the hammer. Plus, you don’t want to break the small diameter pipes. That big hammer has got the power to just destroy everything. It gets a little touchy when you’re talking about six or eight inch diameter lines.”
Melvin said, “Jake knows his stuff! This was a significant project. Directional Service South was the perfect choice for this one. Jake’s crews are well-versed in the extraction process and it shows. High quality from start to finish!”