The Utah Transit Authority (UTA) is working on final construction of a 44-mile commuter based rail line connecting Salt Lake City with the communities to its north. While the task of constructing these rail lines includes many forms of above ground construction, trenchless technology is playing a role as well. Claude H. Nix Construction/Jasco, Inc. (C.H. Nix), Ogden, Utah, was contracted to complete a complicated series of casing installations under the rail line.
According to C.H. Nix Project Manager, Jon Nix, the project kind of fell into their laps. He said, “We actually helped the general contractor, Commuter Rail Constructors, with the preliminary budget numbers for the project. When the boring portion of the project was put out to bid, we did not get the bid. The original bore contractor had been on the project for about four months when they were asked to leave, and we were called. It was an emergency situation when the general contractor called, thanks to the efforts of Jim Moore and TT Technologies, we were able to respond to the project, and help them out of a bad situation.”
C.H. Nix was called in to rescue an auger bore with a 60-inch steel casing that was stuck 40 feet into an 80-foot storm drain bore. The auger had created a void and subsequent 15-foot diameter sinkhole between two Union Pacific tracks. C.H. Nix brought in an 18-inch Grundoram Goliath pipe rammer from trenchless equipment manufacturer TT Technologies, Aurora, Ill. to complete the bore. Once ground water issues were under control and the pit set up, crews were able to complete the ram in short order.
Pipe ramming is a favorite installation method for contractors installing casings under roads and rail lines because the method provides accurate installation in a wide range of soils without surface slump.
In addition, a second 60-inch bore at the location had also been started and not completed. According to Nix, the second casing had been sitting at the 60-foot mark for over three months. Even though the casing had sat idle in the ground for several months, the Nix crew was able to break the casing free with the Goliath rammer and ram the casing an additional 20 lf to complete the alignment.
Nix said, “The most amazing feat for the Goliath Hammer, was when it was able to break free and advance a 60-inch casing that had been 60 feet in the ground for over three months. I was not sure that it would be able to do this, but it did and it did it very well. The Union Pacific railroad and the general contractor were very impressed.” From there, CNC became an integral part of the project, as did pneumatic pipe ramming.
Ramming Basics & Benefits
Trenchless pipe installation through ramming is a fairly simple process. A pneumatic hammer is attached to the rear of the casing or pipe. The ramming tool 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.
According to TT Technologies’ pipe ramming specialist Jim Moore, several options are available for ramming various lengths of pipe. He said, “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. Depending on the size of the installation, spoil from inside the casing can be removed with compressed air, water, an auguring system or other types of earthmoving equipment.”
The C.H. Nix ramming project was completed for a commuter rail line involving construction of approximately 45 miles of new track, running from North Ogden, Utah to Salt Lake City, Utah.
Some casing installation methods are impaired or even rendered inoperable by rock or boulder filled soils. Pipe ramming is different. 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.
Ramming tools, in general, are capable of installing 4- through 147-inch diameter pipe and steel casings. Ramming requires minimal working depths and has proven effective for horizontal, vertical, and angled applications. Ramming is also ideal for installations under roads and rail lines because it displaces the soil without creating voids or slumps.
After freeing and installing the stuck 60-inch casing the crew moved on to the next project site (3rd and 4th crossings) for another storm drain installation. It included two parallel 48-inch steel casings. Difficulties on this site included minimal cover over the casing, less than 18 inches below tracks, very limited muddy access, and proximity to the railroad tracks.
Nix said, “Safety for this entire project is known as ‘Form B,’ which requires full-time safety personnel on site and work must stop completely when trains are in the vicinity, sometimes for 40 minutes or more. The high water table was again a challenge, but once we got things set up, the 90-foot bores took minimal time to complete. We set a company production record on this alignment; we were able to hammer one 20-foot length of 48-inch casing into the ground in nine minutes.”
The third site (5th crossing) was the most difficult. The scope of work included boring under three sets of tracks and into an existing freeway embankment in order to realign an existing pressure irrigation water line. The owner wanted to encase the line in one continuous steel casing across both the freeway and railroad tracks. The existing irrigation line had a horizontal bend in it that needed to be removed and re-aligned.
Prior to construction, no one knew where the end of the existing casing for the irrigation line was located or exactly how deep it was. Nix knew that once they located the existing end of casing, that accuracy in order to line up and bore to the existing end from the opposite side of the tracks would be critical. C.H. Nix crews opted to use an Akkerman pilot tube guided boring system and Goliath pipe rammer to complete this drive.
In several situations the C.H. Nix crew used the Grundoram Goliath in conjunction with a pilot tube boring machine to complete the casing installations. Note the ramming adapter attached to the lead end of the casing.
Nix said, “The pilot tubes would allow us the accuracy, and pipe ramming would assist with the minimal cover, high ground water, and poor soil conditions. To excavate the pit in the embankment, we used soil nails and shotcrete to excavate sequentially down to the existing casing. The casing was about 45 feet deep in the embankment. Once the casing was located, we projected the existing alignment across the tracks and constructed our insertion pit.”
C.H. Nix crews were able to push the pilot tubes, and ram the 36-inch casing 200 lf across the tracks with less than a 2-inch deviation between the existing casing and the newly installed casing. The crews were also able to connect the two by splitting and re-welding a piece of 36-inch casing. Construction also included the installation of 30-inch HDPE through the steel casing.
The 6th through the 9th crossings were completed in the Ogden Rail Yard. A 24-inch steel casing, for a storm drain, was rammed 200 linear feet across seven sets of tracks. The pilot tube system was also used on this drive for line and grade accuracy.
Nix said, “A 20-inch steel casing, for waterline, was rammed 215 lf using our 12-inch hammer. This alignment was challenging due to the fact that we hooked a “ghost” abandoned steel waterline about 190 lf into the drive. It was located directly under a set of active tracks. The railroad would not let us dig up the end of casing using an excavator, but agreed to allow us to use a vacuum truck to “daylight” the end of the casing with a 2-foot diameter hole. Once we exposed the end of the casing, about 12 feet deep, we found the steel waterline wrapped over the end of our casing. Our welder built a custom extra long handled cutting torch, reached down into the “key hole” excavation and cut the obstructing pipe out of our alignment. The obstruction held up advancement of the casing for two days, but our hammer was able to get the pipe string moving again, and complete the bore.”
The 8th and 9th crossings were parallel 60-inch steel casings, for re-alignment of an existing storm drain box culvert. C.H. Nix crews completed both of these crossings using an Akkerman TBM and series 5000 pipe jacking system. Nix used this method because of the pipe size, minimal grade, and tight alignment. They were able to come in on design line and grade with less than 0.05 feet of deviation.
The 10th crossing included the installation of a 36-inch storm drain culvert crossing. It was similar to the others with minimal cover, poor soil conditions, and high ground water. C.H. Nix crews were able to complete the crossing successfully using pipe ramming.
The 11th crossing was completed for a water transmission re-alignment. Nix said, “We rammed 120 lf of 36-inch casing, and slid 30-inch HDPE through the casing. We then installed 16-inch ductile iron pipe on either side of the tracks and connected it to the 30-inch HDPE.”
The final three crossings (12th through 14th) will be constructed in downtown Salt Lake City. They will consist of three 24-inch bores. All three crossings will be completed using pilot tube technology and the Goliath pipe rammer.
According to Nix the project provided many challenges and many rewards. He said, “We have never seen so many bores in varying sizes and lengths on one project before. Also the ground conditions varied greatly, from running sands and silt, to river bottom cobble to stiff clays. The logistics of getting to the job in a very short time, due to the emergency situation, proved challenging, but we were able to mobilize and be on the job within two weeks of the general contractor calling.
“Equipment was also important. The Goliath rammer allowed us to install various sizes of casing in different conditions. This project has been and still is a source of great opportunity for Claude H. Nix Construction. We feel fortunate to have been a part of it.”
About the Author: Jim Schill is a technical writer based in Mankato, MN.