Railway Track & Structures - May 2008 - (Page 32)

Left, TT Technologies was part of a world-record pipe ram project that took place in Altoona, Iowa, which rammed a 147-inch diameter casing for a bike path under track owned by Iowa Interstate Railroad. Miller the Driller was the contractor. Right, 80 feet of 48-inch steel casing installed under a railroad using a 24-inch HammerHead Mole pipe rammer in Bainbridge, Pa. Soil conditions as described by a HammerHead technical specialist on site were “very hard, compact soil with large cobble.” long and 20 feet deep or shallower, Nicholson notes that anything can be accomplished with proper preparation. “The combination of both depth and length become contributing factors. If someone is looking at a 42 -inch pipe ram, 350feet long, 20-feet in the ground, the combining factors make the project very difﬁcult. You are dealing with 20 feet of earth above the casing that creates load throughout the ramming process, in conjunction with a signiﬁcant length of pipe,” said Nicholson. “It’s important the extra time and preparation required to complete a project of this magnitude be fully utilized such as laser site, additional pit preparation, which may include pouring a concrete pad, additional lubrication or bentonite lines, and back up air compressor(s) to ensure any potential down time is minimized. Unlike some other trenchless methods, there is no steering capability with pipe ramming. It is critical that the ﬁrst 10 to 15 feet of the casing go into the ground as perfect as possible because that will have great impact on the overall success and accuracy of the project.” Although pipe ramming is used primarily for horizontal applications, it can be used for vertical installations such as pile driving or micro-piling. According to Nicholson, in order to have a successful vertical ram, a device or structure is needed to hold and lift the pneumatic hammer at the proper height and angle. Ground conditions are a big factor when considering whether or not a project would beneﬁt from pipe ramming. “Pipe ramming can be used in any soil type, but the method excels in mixed-face materials and granular soils that can cause problems for boring techniques that utilize rotational soil removal methods,” said Holcomb” Nicholson agrees, “Pipe ramming will stand out in running soil and cobble, clay is a 50-50 toss up [between ramming or auger boring] and heavy encrusted rock situations are where an auger will have a beneﬁt because I can’t drive a steel casing straight through rock.” Jason Clark, president of Iowa Trenchless, is currently using the process based on ground conditions. “We’re ramming 32 Railway Track & Structures May 2008 in Bark River, Mich., and the ground would not allow us to do anything but ram because it’s unconsolidated material,” said Clark. According to The Trenchless Technology Center, pipe ramming can save both installation time and costs under favorable conditions, when compared to other trenchless methods. “Some casing installation methods are impaired or even rendered inoperable by rock- or boulder-ﬁlled soils,” said Holcomb. “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. This means that there will be no undermining of the tracks regardless of the type of soil encountered. Additional advantages include no requirement for a back abutment to push against, the ability to use casing lengths of any length up to and including 150 feet, the capability to ram a larger casing over top of an existing culvert and then remove the old culvert from inside the new casing.” For Clark, the key advantage is reducing ground loss. “When you bore you can lose ground, but when you’re pipe ramming you can’t.” “One of the distinct advantages would be speed; you can typically insert the casing much more quickly because one of the factors with auger boring is that they are removing the soil as they make the bore,” said Nicholson. “The ability to go through certain soils that auger bores can not go through is certainly an advantage. Typically, you’re dealing with running soil, if you’re removing soil as you go, it’s hard to know if you’re creating a void.” www.rtands.com Advantages Ground conditions matter http://www.rtands.com

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Railway Track & Structures - May 2008

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