Over the last 30 years trenchless technology has emerged as one of the premier underground construction methodologies. New techniques are continually being developed, while existing techniques are being refined. This type of growth in technology can be seen in the gas industry and its contractors.
Premiere pipeline installation contractor US Pipeline, Houston, TX is a good example of a company embracing new technologies and helping develop new methods and ways of construction. Recently, US Pipeline was contracted to install 28 miles of 36-inch gas pipeline for the Horizon Pipeline project taking place in northern Illinois. While a large portion of the project was open-cut, trenchless technology played a major roll in certain areas.
Faced with numerous road crossings, rail crossings and other situations where traditional open-cut construction would not work, US Pipeline Vice President Jimmy Crotts opted for a trenchless installation method. He decided to incorporate pneumatic pipe ramming into the slick-bore process. This trenchless process allowed US Pipeline crews to install pipe under roads, rail lines and other areas effectively and efficiently. The results were impressive.
According to Crotts, the process is simple yet effective. He said, “Basically what we’re doing is installing a bore pipe under a road or railway, etc. Once the pipe is in place, we attach the product pipe to the bore pipe. Then, we remove the bore pipe with a winch. As the bore pipe is removed the product pipe is pulled in place.”
The US Pipeline crews used pneumatic pipe ramming during the slick bore process to install the bore pipe. For the Horizon project the crews used two 18-inch diameter Grundoram Goliaths from trenchless equipment manufacturer TT Technologies, Aurora, IL.
According to TT Technologies Pipe Ram Specialist Scott Kneip, there are advantages to ramming in the bore pipe. Kneip said, “The soil conditions in the area where the US pipeline crew are working are not very conducive to auger boring. The glacial till soil contains many rocks and boulders that can play havoc with a conventional auger bore system. Ramming is a preferable option.”
Gas Goes Trenchless
The gas industry has been a leader in the development of new construction technologies. Motivated by deregulation to find more efficient ways of doing business, the distribution side of the industry has embraced trenchless technology for maintaining/upgrading existing systems as well as installing new ones.
The distribution segment has been instrumental in the wide scale use and acceptance of directional drilling. Gas utilities are also active users of pneumatic piercing tools and are responsible for the development of the only guided piercing tool technology.
The transmission side of the industry has also adopted trenchless construction methods. Some of the methods, i.e. directional drilling, are the same, but others are quiet different. Piercing tools are ideal for the distribution side of the industry because of the smaller pipe diameters (1/2-inch to 6-inches) and different working conditions. Piercing tools are not effective for installing 36-inch or 48-inch natural gas pipelines.
Auger boring is one method has been a staple of the gas pipeline industry for years. The method is extremely effective in certain areas, but augering under roads and rail lines creates the possibility for costly surface slump and voids. Over the last several years a pipe ramming has gained greater attention in the gas industry and its effectiveness in the slick bore process.
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.
Trenchless pipe ramming is simple; a pneumatic hammer is attached to the rear of the bore pipe. The ramming tool, which is basically an encased piston, drives the pipe through the ground with repeated percussive blows.
A cutting shoe is often welded to the front of the lead casing to help reduce friction and cut through the soil. Bentonite or polymer lubrication can also be used to help reduce friction during ramming operations. For the Horizon project, the US Pipeline crew used both a specially designed cutting-head on the lead end of the bore pipe and Bentonite lubrication to help with ramming operations.
Several options are available for ramming various lengths of pipe. An entire length of pipe can be installed at once or, for longer runs, one section at a time can be installed. In that case the ramming tool is removed after each section is in place and a new section is welded on to the end of the newly installed section. The Grundoram is connected to the new section and ramming continues. Depending on the size of the installation, spoil from inside the casing can be removed with compressed air, water, a pig system, an augering system or a combination of techniques.
Crotts described the process his crews went through for ramming in a several hundred-foot bore pipe installation on the Horizon project. He said, “We’d ram a section of bore pipe, say 80 feet, under a wetland or a road. Then clean that bore pipe out using a conventional auger boring machine. Then we would weld on another 80-foot section of pipe and ram that in. Then clean it out. Cleaning out as during ramming takes the weight out of the pipe and provides better control. Once we have the bore pipe in place, then we can weld on the carrier pipe and pull it in.”
Once the product pipe is installed, the bore pipe can be used again for the next slick-bore.
Ramming & Slick-Bore Benefits
According to Kneip slick-boring and ramming are particularly conducive to transmission pipeline installation. He said, “Typically, crews have a decent amount of room on either side of road or rail crossing. This allows them to install longer sections of pipe. But even in tighter working areas, they are still able to ram in the bore pipe section by section and install the product pipe section by section.
“Slick-boring also limits the amount of stress placed on the product pipe, which is of concern to project owners. The bore pipe ends up taking to brunt of impact from the ramming in tough soil conditions and spoil clean out. Through ramming it can also be installed very accurately. The product pipe is pulled into its ideal position without being subjected to much of anything.”
Ramming can also overcome rock or boulder filled soils. During pipe ramming, boulders and rocks as large as the casing itself can be “swallowed up” as the casing moves through the soil and can be removed after the installation is complete. This also allows for a significant level of accuracy and makes ramming ideal for installations under roads and rail lines because it displaces the soil without creating voids or slumps.
Crotts said, “If we weren’t using this ramming method the conventional way would have been to auger bore. But what happens much of the time is that you begin to experience an undermining of the road. You get caverns and cavities and the road slumps. We have not had to maintain any road that we bored under using the ramming technique.”
The technique proved especially valuable for a section of the project that took place under Interstate 90. Crotts said, “The project specifications called for the installation under the I-90 toll-way to be hand tunneled. We invited the State engineers with the toll-road department to come out watch what we were doing. They saw the operation and gave us permission to ram under I-90.”
The US Pipeline crew’s skill at ramming and slick-boring paid off in many sections of the Horizon Pipeline project. Over the 28-mile long installation, the crew performed over 60 slick-bores in many different situations. Crotts said, “We did some roadways, rail crossings, creeks and even wetlands. In one county working through designated wetland areas was prohibited so we were required to use some type of boring. We rammed and slick-bored through those areas. It worked very well.”
During the project Crotts and the US Pipeline crew completed some very substantial installations in terms of length with the Grundoram. According to Crotts, short installations averaged 60 feet, while the long installations ran near 300 feet. The US Pipeline crew successfully completed one slick-bore totaling an impressive 380 feet with 36-inch pipe.
Everyone associated with the project was excited about the success the US Pipeline crew had with the Grundoram and the slick-bore process. Kneip said, “Jimmy and his crew really did some incredible installations on this project with the slick-bore/ramming method. They’re a top-notch pipeliner all the way.”
Crotts said, “I don’t think we would have been able to complete the project the way we did, without the use of this process. I know we would have had a lot of road maintenance. For the type of soil conditions we were in, the glacial till, cobble, sandy etc, I think ramming with the slick-bore will take the industry by storm. The chance for us to be more competitive is there too. It’s a great opportunity.”
by Jim Schill
ACP, May 2002