Pipe Ramming in the Thin Air: BTrenchless Goes Large Diameter
Pneumatic pipe ramming continues to prove that it is one of the most versatile and effective trenchless methods. With much of the attention being placed on pipe ramming’s effectiveness for assisting directional drilling operations, it is easy to overlook pipe ramming in its more traditional role of casing installation. BTrenchless (a division of BT Construction), Henderson, Colo. recently showed just how effective pipe ramming can be for large diameter casing work.
According to Mark Wellensiek, BTrenchless Boring General Superintendent, the company has progressed from smaller diameter pipe rams to tackling large diameter projects. He said, “We’ve done about six pipe rams so far. We started with 24-inch and 30-inch diameter casings, then completed several 42-inch diameters and worked our way up to this 84-inch ram.”
For the 84-inch diameter, 80-foot pipe ram under Highway 160 in Pagosa Springs, Colo., BTrenchless used a 24-inch diameter Grundoram Taurus pneumatic pipe rammer from trenchless equipment manufacturer TT Technologies, Aurora, Ill.
BTrenchless is one of Colorado’s largest trenchless contractors, offering a variety of trenchless construction techniques for utility system installations and replacement of water, storm, and sanitary sewer lines and conduits. As a division of BT Construction, Inc., BTrenchless has over 25 years of utility construction experience. By maintaining a large inventory of equipment and employing a large number of skilled professionals, BTrenchless has the resources necessary to successfully complete projects on time and on budget. The company’s trenchless capabilities include: microtunneling tunnel boring, hand tunneling, guided (pilot tube) auger boring, horizontal auger boring, pipe ramming, horizontal directional drilling, pipe reaming and vacuum excavation.
The project in Pagosa Springs drew heavily on the company’s construction experience and trenchless expertise.
According to Wellensiek, the original CMP multi-plate culvert installed in 1958 had collapsed. In addition, a sinkhole was developing on the northeast side of the intersection of US 160 and 8th Street. The drainage casing is part of a larger drainage system that directs run-off from the San Juan Mountain Range, through town of Pagosa Springs and into the San Juan River. Continuous flow through the culvert has made the sinkhole a significant problem. The edge of the sinkhole was only 25 feet from the north shoulder of west bound US 160 and the portion of the existing culvert under Highway 160 was so deteriorated that the Colorado Dept. of Transportation (CDOT) determined that the pipe needed to be replaced.
Wellensiek said, “As the main artery between Pagosa Springs and Durango, Colo, Highway160 is a very busy two lane highway and CDOT did not want to impact traffic by open cutting the highway to install a new culvert. Open cutting was really never an option. We would have had to perform that type of work late at night when traffic levels were as low as possible.”
Ultimately, plans were drawn up to ram an 84-inch diameter steel casing over the deteriorating 60-inch CMP culvert and encase it. The existing CMP would then be removed from the steel casing and a new 60-inch RCP line installed. The BTrenchless crew would face many challenges in order to make that happen.
Pipe Ramming 101
During the pipe ramming process, a pneumatic hammer is attached to the rear of the casing or pipe. The ramming tool, which consists of a piston within a casing, drives the pipe or casing 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. Ramming tools, in general, are capable of installing 4- through 147-inch diameter pipe and steel casings.
Ramming can be used for horizontal, vertical, and even angled applications. It is often used under roads, like the Pagosa project, and rail lines because it displaces the soil without creating voids or slumps.
According to TT Technologies pipe ramming specialist Rick Melvin that is a key benefit of pipe ramming. He said, “Some installation methods can jeopardize the integrity of roads or rail lines because they remove soil from underneath to allow for the new pipe installation. Pipe ramming’s ability to install various sized casings without putting the topside structures in danger makes it a very attractive option. Also pipe ramming works in difficult soil conditions. 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.”
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 ramming tool is connected to the new section and ramming continues. Several methods can be used to remove spoil from the casing including compressed air, water, an auguring system or other types of earthmoving equipment.
High And Not So Dry
One of the first challenges Wellensiek and the BTrenchless crew faced was elevation. Wellensiek said, “Pagosa Springs sits at an elevation of 7,100 feet above sea level. That has a direct impact on the capacity of your air compressor system.”
Another difficult aspect of the project was maintaining drainage flow through the existing culvert while ramming. Wellensiek said, “At times there was really low flow. Twice during this project we were completely flooded out because of rain and there was no way to handle that amount of water. So basically we stopped, and got out of the way. There was nothing else we could do.”
On The Job
BTrenchless crews excavated a ramming pit on the south side of the road and prepared a ramming pad by layering approximately 18 inches of inch-and-a-half rock in the bottom of the pit. Once complete crews assembled the 60-inch jack and boring machine. The rails of the machine were used to support and guide the new 84-inch casing during the pipe ramming process.
Once the casing was placed in position, crews made the connection between the 84-inch casing and the 24-inch pie rammer. Melvin explained, “The connection between the tool and the casing is made through a tapered ram cone and 84-inch cotter segments. This configuration ensures that the maximum driving force is transferred to the pipe. In the past, ramming a casing of this diameter would have required a fabricated ramming adapter, but as the demand for larger and large diameter ramming equipment has increased, we (TT Technologies) now offer standard ramming gear for casing diameters as large as 96 inches. This saves time and money for the contractor.”
According to Wellensiek, removing the existing CMP pipe was a challenge once the ramming was complete. He said, “When the new casing was hammered over an existing pipe we encountered some 30-inch minus rock during the process. These rocks were pushed into the existing CMP. In addition, as the casing was hammered, the ground was compressed around the existing CMP multi plate. We needed use an acetylene torch to cut the CMP into 10-foot sections. Then, we pulled out those sections with the boring machine.”
After the old CMP pipe was removed and all the spoil cleaned out, the new 60-inch RCP culvert was jacked into place. Fly ash was used to fill the annular between the new 60-inch pipe and the 84-inch casing.
Wellensiek was impressed with the results. He said, “I was really pleasantly surprised that that 84-inch casing went across there as quickly as it did. The real challenging part was maintaining the water flow through there. But now that we’ve gotten through that, we know we’d be able to do it again.”
Melvin said, “The BTrenchless crew really did a great job on this project. It was very challenging from start to finish, but these guys know what they’re doing and do it well.”
Underground Construction, December 2007