Nothing displays the
benefits and capabilities of directional drilling better than
a river crossing. While these crossings have become commonplace
over the last 15 years, they still present distinct challenges
for drill operators and equipment. Difficult soil conditions under
river bottoms and hydrostatic pressure from the river itself can
combine to create problems during drilling applications. The drill
rig seizing during product pullback, a condition often referred
to as hydrolock, is one potential problem. Utilizing a pipe ramming
tool during pullback is how one Minnesota contractor solved this
problem.
Hugo, Minnesota based Lessard-Nyren
was recently contracted to install 600 feet of 6-inch pipe under
the Sauk River on the Northern side of St. Cloud, MN. The first
contractor failed to complete the pilot bore under the river
in extremely rocky and sandy soil conditions. Lessard-Nyren
accepted the challenge.
Using an Advantage 8000 directional
drill rig with 80,000 lbs. of pullback, the Lessard-Nyren crew
was able to complete a pilot bore under the river. On the other
side, the crew attached a 14-inch back reamer and attempted
to pull back 6-inch HDPE SDR 11. Once in place, the pipe would
house 3 innerducts for fiber optic cable.
The crew pulled the HDPE approximately
400 feet before it seized in the rocky soil. The Advantage rig
was powerful enough to pull the SDR 11 pipe apart. Crew supervisor
Greg Jungwirth re-evaluated the job and decided to employ a
different strategy. Jungwirth believed the crossing could be
completed using a pneumatic pipe ramming tool to assist during
product pullback. He turned to Mike Tjader and pipe ramming
tool manufacturer TT Technologies, Aurora, Illinois, for technical
support.
Tjader explains, "Seized drill
stems or product pipe can often be freed by using a pipe ramming
tool. The tool is attached to the end of the product pipe and
when pullback slows or stops, the tool is started. The percussive
action of the rammer helps move the pipe through the difficult
section."
The Lessard-Nyren crew completed
a second pilot bore parallel to the first. Again a 14-inch back
reamer was attached and pullback began. This time the crew pulled
5-inch steel pipe and used a Grundoram Hercules pipe ramming
tool from TT Technologies.
The crew was able to pull the 5-inch
steel pipe to within 200-ft of shore before the reamer wore
out. Tjader said, "We tried to coordinate tapping with
the rammer and pulling with the drill, but the reamer wasn’t
cutting anymore. We decided to try and remove the pipe."
Using the Grundoram Hercules, the
crew rammed the pipe forward until they broke free of the drill.
The rammer was then reversed and removed about 100 feet of the
pipe. According to Tjader, the crew then attached a bracket
to the pipe and pulled the remaining 300 feet out with a backhoe.
Without the pipe attached, the crew was eventually able to complete
the bore with the worn out reamer.
Using a different reamer, the Lessard
Nyren crew set out for a third attempt. Tjader said, "In
order to avoid damage to the product pipe, we decided to set
a pull limit of 40,000 lbs. When we reached that level, we would
start the pipe ramming tool to help with the pullback."
The crew followed the last bore path.
Once on the other side, they attached a new 15-inch reamer and
began pulling back the 5-inch steel pipe. Tjader said, "We
got about half way through the 600-ft run before the pulling
tension reached 40,000 lbs. We started the Hercules and tapped
on the pipe. We ran the hammer at 35% power for about 4 feet,
until the pipe loosened up. We continued that way for the last
several hundred feet, until completing the pullback."
The crew was extremely pleased by
the results. Tjader said, "I guess third time’s a
charm. It was a tough job. It took a lot of patience and know-how
on Lessard-Nyren’s part. A little help from the pipe rammer
didn’t hurt either."
Utilily Contractor,
November 1999, Page 30
