Pneumatic pipe ramming continues to be utilized in a wide range of applications, both for primary pipe installation and as a method to help facilitate the installation or removal of other pipes or products. The advancement of pipe ramming continues to develop into new applications with innovative ideas and techniques for achieving trenchless outcomes on projects with extraordinary requirements and restrictions.
Recently, Laney Directional Drilling, Spring, TX, utilized two pneumatic pipe rammers to complete a challenging pipe extraction that required the contractor to break loose pipe that had been in the ground for over 60 years.
As part of the EPA’s Waterways of America program, Exxon Mobile needed to upgrade a steel petroleum line under a section of the Colorado River that runs through Texas. Laney Directional Drilling was brought into the project to install the new petroleum lines through horizontal directional drilling. However, the installation of the new line was only half the battle. The EPA also mandated that the existing steel line, installed in the 1950’s, be removed from under the waterway. That meant extracting the existing 1,110-foot, 8-inch steel main, after installing the new main. Laney approached trenchless equipment manufacturer TT Technologies, Aurora, Ill., to assist in the development an extraction option utilizing pneumatic pipe ramming.
Pipe ramming specialist Rick Melvin, TT Technologies said, “After taking a look at this project, we figured that it was going to require some serious force to get that pipe out of the ground. We went with a 24-inch diameter Grundoram Taurus and an 18-inch diameter Grundoram Goliath pneumatic pipe rammers. These two rammers, used in a push and pull configuration would provide a substantial amount of combined percussive force.”
Pipe Ramming & The Development of Extraction Techniques
While several pipe ramming techniques have been introduced over the years to help directional drillers install pipe, several techniques have also been developed to help drillers salvage drill pipe and drill stems that get stuck during installation. It was the combination of these techniques that served as the basis for developing an extraction technique that would be effective for the project under the Colorado River.
Melvin said, “The HDD Assist ramming techniques are designed to break the friction of the pipe string and either keep the pipe moving or remove the pipe or drill string altogether. On the installation side, pullback assist helps drillers overcome a condition called hydrolock, a condition that happens when the external pressure being put on the product pipe from ground water pressure, drilling fluid pressure and/or soil conditions exceeds the drill rig’s pullback capability or the product pipe’s tensile strength. This often happens when drilling under bodies of water or rivers.
“By placing a pneumatic rammer on the back of the product pipe and tapping on it, contractors can overcome hydrolock or prevent it altogether. The percussive action of a pipe rammer in this situation is used to help free the immobilized pipe and keep it moving in during pullback.”
On the removal side, several pipe ramming techniques to used remove stuck bore pipes and drill stems also contributed to the Laney extraction project.
Melvin said, “With a bore salvage set up, you’ve got the pipe rammer attached to the end of the stuck product pipe. In this case, the rammer is not pushing the pipe in, instead it is attached through some sort of fabricated sleeve and the percussive force is generated outward to try and free the pipe and ultimately remove it.
“This set up is similar to drill stem recovery where the rammer is connect to the stuck drill string through a fabricate adapter and the percussive force is used to extract the drill string. In some instances, however, the rammer can be used to push on the drill string while the drill rig pulls back. Both of the installation and removal methods were used to some extent on this project.”
For the project under the Colorado River, Laney used modified versions of the HDD Assist techniques to remove the 60-year-old main.
Making the Connection
Laney crews estimated that the existing pipe would be able to withstand approximately 250,000 lbs. of pulling force. Through series of consultations, a two-tiered approach was developed that included a braided cable blocking system and two pneumatic pipe ramming tools, one on the extraction side of the pipe providing percussive pulling force and one on the insertion side of the pipe providing percussive pushing force.
Melvin said, “This pipe had been in the ground for years, so we figured that it might take more than just the push and pull of the pipe rammers to extract it. So Laney crews devised an impressive block system to harness the power of their dozers. This set up adds a static force that compliments the percussive force being generated by the rammers.”
The 400-ton, 12-part block system was created to supply static pull force on the extraction side of the pipe. A D-8 Cat dozer winch applied the pulling force to the block system utilizing 1.25-in. diameter cables.
Melvin said, “We had several meetings to determine what was the best way to approach the connection between the 24-inch rammer and the pipe. We decided on an extraction cylinder that would encapsulate the rammer.”
Based on those meetings, designs for a 36-inch diameter extraction cylinder to house a 24-inch diameter pneumatic pipe ramming tool were developed. The objective of the cylinder was transfer the percussive pulling force from the pneumatic pipe rammer to the existing 8-inch steel pipe, as well as the static pull force from the block system. Wings on each side of the cylinder made the connection to the block system through the braided cables.
On the extraction side of the river, Laney crews were able to expose approximately 250 feet of the existing pipe and created an exit path for the pipe to follow as it was being extracted.
The cylinder was placed over the ramming tool so that the body of the tool came up through the top, however the rear flair of the tool was contained within cylinder, making the final connection with the rammer. The connection between the extraction cylinder and the 8-inch steel pipe was made with a fabricated sleeve that reduced from 36 inches to 8 inches. A section of 8-inch heavy wall pipe was welded in place and made the final connection between the sleeve and the existing main.
On the other side of the river, the insertion side, approximately 150 feet of pipe was exposed and a ramming pit was created. A fabricated ram cone with a section of new heavy walled 8-inch steel pipe was used to make the connection between the 18-inch diameter pneumatic pipe ramming tool and the back of the 8-inch steel pipe. A cradle, held in place by an excavator, supported the rammer.
At the start of the extraction, crews began by applying percussive force from the insertion side of the pipe, effectively ramming the pipe. Soon after, static and percussive pulling force was added on the extraction side and the pipe began to move.
Melvin said, “It took a little persuasion, but the pipe finally began to come loose. It’s a rather impressive feat of engineering and skill by the Laney crews. That pipe had been underground for almost six decades. To be able to remove it, whole, in one piece, is quite an accomplishment.”
From start to finish the project took 18 days, including all the prep work and final restoration. The actual extraction of the pipe took 3 days to complete. The entire 1,110-foot length of pipe was extracted in a single piece.