Underground Installation Projects: Determining the Best Approach

August 2008 Vol. 63 No. 8

Jason Clark, owner and president of Iowa Trenchless in Panora, IA, recently used a pneumatic hammer and auger boring machine to upgrade a storm water system near Rockville, MN. The project called for installing 100 feet of 60 inch and 80 feet of 30 inch storm water lines under a Burlington Northern Railroad track. The only problem? Rocks. And lots of them.

The ground below the railway bed was mainly cobble and coarse wet sand. Boring or pipe jacking were not options due to the high risk of a hole opening caving in or collapsing due to the unstable ground conditions. But the resourceful Clark, after some thought and planning, figured he could use a pipe rammer to complete the project with some modifications to the plan.

“In these types of ground conditions, rammed pipe can swallow the material whole, including large rocks and cobble, keeping the pipe outside diameter to a minimum and saving cost on the job,” Clark says. “The material is not removed until after the casing is installed, reducing the risk of creating voids.”

The project required that the pipe be placed more than six feet underground with the two drainage lines installed at a 45 degree angle horizontally under the railroad bed – all while trains continued to pass on the tracks above.

Iowa Trenchless rented a 24 inch pneumatic pipe rammer from HammerHead to install the heavy wall steel pipe. When the full length of pipe was installed, the crew used an auger boring machine to remove the soil, cobble and sand that had accumulated inside the 60 inch and 30 inch pipes.

“I don’t think anyone knew what they were getting into at the time,” Clark says. “There was just no way to bore this project. But with some flexibility and ingenuity we were able to complete it successfully.”

Gasmovic has also worked with contractors who have used a directional drill to bore a pilot hole and then modify a boring machine to tie into the pilot stem. They then use the pilot hole as a guide to install a large diameter pipe with an auger.

Dilemma

For some contractors, using more than one trenchless method presents challenges. Most adversely affected is the smaller, independent operator who must prioritize equipment purchases based on the type of services they offer and perform most often. Many don’t own the equipment needed to perform all of the various approaches. Access to employees with the skills and knowledge to operate the machines specifically designed to perform varied applications also presents a dilemma.