Contractor Miller the Driller used a 24-inch-diameter Grundoram Taurus pneumatic pipe rammer from TT Technologies to install a tunnel for a bicycle trail underneath railroad tracks in Altoona, Iowa. Photos: Miller the Driller and TT Technologies
The completed tunnel used a 147-inch OD casing; the largest diameter casing ever successfully rammed, it topped the old mark by 3 inches.
Record Ramming

The connection between the Grundoram Taurus and the casing was made using a special adapter. The 147-inch, inverted-bell, pipe adapter, rolled by Arntzen Steel, Rockford, Ill., reduced the overall diameter to 80 inches. An 80-inch ram cone was then connected to the adapter and further reduced the diameter to 30 inches. A 24-inch ram cone made the final connection to the tool. The entire configuration was secured with tensioning chains and the tool was connected to the air compressor.

The actual ramming went smoothly. Crews were able to install the first 20-foot section of casing without incident. The ramming tool was removed and some of the spoil was taken out of the casing. Crews then positioned the next 20-foot section of pipe in place and made the connection to the first section. The rammer was reconnected and the second section was rammed in place. The entire ram was completed on a 2.2% downhill grade. Once all of the casings were installed, the Miller the Driller crew removed the remaining spoil with a skid-steer loader. Almost 6000 cubic feet of dirt was removed from the casings.

Young attributes the success of the project to several factors. “The willingness of the engineers to look beyond conventional construction techniques and allow a trenchless solution to be developed was the first part of the success,” he said. “The crew was very professional and courteous at all times. Our field supervisor Bill Mendenhall took hold of a concept and made a highly difficult project highly successful. Several railroads were watching this project very closely. They couldn't believe it when we rammed the pipe through to the exit side and never disturbed the tracks.”

“[Community] response has been great,” said Willey. “The kids, as well as adults, can access the old swimming pool, the new aquatic center, the fitness center, library, and playfields—all without having to worry about crossing the railroad tracks.”

Jim Schill is a Mankato, Minn.-based technical writer.