Trenchless pipe ramming continues to prove its value, especially in situations that require quick mobilization, effective casing or culvert installation and extra care regarding surface protection in sensitive areas like roadways and rail lines. Last year’s massive rainfall event in Colorado created just that type of situation.
In September 2013 a frontal boundary stalled over Colorado resulting in catastrophic flooding along the front range of the Rocky Mountains. According to the National Weather Service, the rainfalls and the resulting floods amounted to a 1/1000-probability event, more commonly referred to as a 1,000-year flood. Jefferson County, Colorado was one of 14 counties declared as disaster areas by the federal government.
Existing culverts could not keep up with the heavy rains, and water backed up behind embankments, eventually causing destruction of existing culverts or causing entire railroad embankments to wash out. To mitigate additional washout and prevent further damage to the rail lines, Horizontal Boring & Tunneling Co.(HB&T), Exeter, Nebraska, was contracted by a major rail carrier to install several culverts to facilitate the drainage required to handle rainfall and runoff. The project initially included four crossings with 48-inch diameter casings, 235 LF each.
For the project HB&T utilized pneumatic pipe ramming with a system and equipment from trenchless equipment manufacturer TT Technologies, Aurora, Ill. Pipe ramming specialist Dave Holcomb provided technical assistance on the project. He said, “This was a challenging project from the start, but Kenton Moore and Horizontal Boring & Tunneling was the right choice for the job.”
Established in 1982, Horizontal Boring & Tunneling Co. has over 31 years of experience specializing in various methods of trenchless construction. Horizontal Boring & Tunneling Co. serves approximately fifteen states throughout the Midwest each year. HB&T crews have completed numerous difficult trenchless projects under rivers, railroads, highways, and interstates.
As a full service underground construction contractor, HB&T offers a range of trenchless methods and services including auger boring, pilot tube-guided boring, tunneling and micro tunneling, pipe ramming, pipe jacking and rock drilling for water, sewer, electrical, drainage and other utility applications. The ramming project in Jefferson County, Colorado would put those years of experience to the test.
During the pipe ramming process, a pneumatic hammer is attached to the rear of the casing or pipe. The ramming tool 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 and rail lines, like the Colorado, project because it displaces the soil without creating voids or slumps.
According to TT Technologies pipe ramming specialist Dave Holcomb 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, as was the case with Horizontal Boring & Tunneling in Jefferson County. 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.”
Moore said, “This is why we decided on ramming because we didn’t have to worry about impacting the rail lines. You’re effectively swallowing that material up and only displacing the wall thickness of the casing. And that was the objective, we didn’t want to impact the railroad tracks.”
During pipe ramming operations, 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.
Holcomb said, “Ramming tools, in general, are capable of installing 4- through 144-inch diameter pipe and steel casings. At 24 inches in diameter, the Grundoram Taurus, which HB&T used, is one of the world’s largest pipe rammers. The Grundoram Apollo at 32 inches in diameter is the world’s most powerful ramming tool.”
On The Job
The project initially started as four 48-inch diameter, 235 LF crossings, replacing culverts that had washed out with the railroad embankment. The culverts were to be rammed through newly placed fill. Other contractors were working on completing the fill at the same time Horizontal Boring & Tunneling Co. was ramming the new culverts in place.
The remote location of the crossings in the mountains added an extra dimension of difficulty to the project. All of the equipment and material for the project was loaded on work trains and tracked to the job sites and crews, and equipment had to travel through as many as fifteen tunnels to reach bore sites. Coordinating equipment and material movement with the railroad and other contractors posed a challenge at times. Only one track was available to move personnel, equipment, material, rock fill and any other items to several different sites along the rail.
Mobilization to site and prep work began in early October 2013. Because of the critical nature of the project, HB&T crews planned to work 7 days a week until completion. For one week during mid-October, HB&T crews ran one 24-inch diameter Grundoram Taurus pipe rammer for 24 hours a day. After the 24-hour per day shifts ended, HB&T added an 18-inch diameter Grundoram Goliath pipe rammer and worked day shifts only.
A typical connection between the 24-inch diameter Taurus and the 48-inch diameter casing was accomplished with standard ramming gear, consisting of a tapered ram cone and cotter segments designed for ramming 48-inch diameter casing. This configuration ensures that the maximum driving force is transferred to the pipe.
Moore said, “Due to several crossings with lengths in excess of 200 LF and the presence of rock, the crossings would not have been possible without using a Taurus hammer.”
While HB&T was on site, surveying crews worked to identify more locations that needed fill placed and/or additional drainage. Eventually, two crews were added to the first in order to complete the additional work.
Starting in early November, a second Taurus was added to bring the total to three hammers on site. All crews on site took one week off for the Thanksgiving Holiday, and hammering and some demobilization was completed before Christmas with demobilization of remaining equipment taking place in January. In total, 12 crossings totaling 2,567 LF were completed, two by auger boring and ten through pipe ramming.
Towards the end of the project, winter conditions made starting and operating diesel equipment a challenge at times, but the crews on site rose to the occasion. At one point, temperatures dropped enough that it was necessary for air compressors to be left running to prevent the diesel fuel from gelling up.
Holcomb said, “HB&T did an outstanding job considering the difficult conditions. Definitely puts them in the elite pipe ramming contractor category.”