AKKERMAN BUILDS SPECIAL
MACHINE FOR DAM RENOVATION
Originally printed in "Underground
Construction" January 2004
Word of the Standley Lake Dam
rehabilitation project was making the rounds among contractors and
suppliers in the microtunnelling industry long before plans were
completed and it came out for bid.
“We had heard the job would require a large diameter machine with long drives through rocky conditions with the added challenge of having a ‘we’ retrieval of the microtunnel boring machine (MTBM),” says Carl Neagoy of Akkerman Inc., Brownsdale, MN. “There were a lot of interested parties, and Akkerman was tracking the project like everyone else.”
Michels Pipline Construction, Brownsville, WI, got the contract to make two MTBM installations of 72-inch diameter intake microtunnel lake taps.
“Michels is a good
customer and owns Akkerman microtunneling machines and operating
systems, and we were pleased to be asked by Michels to provide a
machine for this project,” Neagoy continues.
Neagoy and Akkerman President Maynard Akkerman met with Pat Michels and
Kevin Michaels and Bill Weltin to discuss MTBM requirements for the
project.
Design Issues
“The original idea was to up-size a previously-built model to
accommodate the Colorado project,” says Neagoy. “But plans often change
and this one soon did, too, Michels personnel decided that the machine
should be more powerful. So we up-sized the motor from the originally
specified 150-horsepower, water-cooled, electric main drive motor, to
200 horsepower, and ultimately to 250 horsepower. Now the MTBM had
become a new design and was still evolving.”
The next challenge was changing the overall length of the machine. Ordinarily, Neagoy says a MTBM is a two-section machine. Because an exit shaft would have to be constructed in the lake bottom, at depth, the plan called for as small a hole as possible. This led to the next design change in the MTBM.
“Instead of two sections of machine measuring approximately 25 feet in total length, Neagoy continues, “there would now be only one shorter section MTBM in order to fit it into the small reception shaft and be able to pull it out of that 20-foot exit hole.”
Another issue primarily relating to concerns about the geology and behavior of the anticipated ground conditions, was that the MTBM should have an independent form of advancement control at the heading.
“The geology indicated a type of clay stone that could exhibit squeezing tendencies, especially when exposed to water,” explains Neagoy. “Because one of the drives was long, there was concern that the main jacks might not be able to be controlled with enough finesse over the long length of tunnel, because the squeezing ground might impede progress and lead to a surging motion, possibly plugging the cutting face or damaging the cutting wheel.
“A decision was made to put a ‘jacking can’ (basically a sealed intermediate jacking station), in line directly behind the MTBM, on the front end of the tunnel. This would allow the operator more precise control of advance rates of just the MTBM, on the front end of the tunnel. This would allow the operator more precise control of advance rates of just the MTBM, and the tunnel could be jacked up behind it using the main jacks. The jacking can would also require a hydraulic power source in the heading, to avoid the need for long oil lines up the tunnel from the shaft, and the heat and potential environmental mess that they could cause.”
To eliminate the second trailing section portion of the MTBM, and also to be able to position a hydraulic power pack close to the MTBM jacking can, Akkerman engineers built some of the components onto two sleds that would ride inside the jacking pipe behind the MTBM. The tunnel booster pump was mounted on one of the sleds, along with some of the control electronics, and the hydraulic power pack was mounted on the second sled. At the end of each drive, the sleds were simply pulled back out of the tunnel when the slurry lines and power cables were stripped out. Then all that was necessary was to close off the bulkheads to permit the wet retrieval of the MTBM.