Underground Construction - September 2019 - 22

Jeff Griffin | Senior Editor

Canopy Pilot-Tubes Provides
Unique Project Solution
Installing pipelines or utilities beneath active roadways is always
a challenge. Highway departments are concerned that excavations
beneath their roadways could settle or create sinkholes in the
roadway alignment, damaging the road. Owners of facilities don't
want heavy weight and vibration of road traffic passing overhead
to damage them.
LRL Construction recently completed a project to replace a
failing 6-foot-diameter corrugated steel drainage pipe under a busy
two-lane U.S. Highway 101 in Manzanita, OR, a scenic, seaside
village on the Pacific Ocean in the northwest part of the state.
To construct the new tunnel, LRL installed an underground
canopy system consisting of 36-inch-diameter steel pipes installed
by the jack-and-bore pilot tube method.
"As far as we know," said CharDee Richey, assistant project
manager for LRL Construction, "this is the first time this method
has been used for this type of application."
The project owner was the Oregon Department of
Transportation (ODOT). Engineers for the project were ODOT and
Randy Zeiger. LRL assisted in the design of the project.

Design
The canopy consisted of 14, 144-foot-long canopy tubes of
36-inch-diameter, schedule-120 steel, ultimately creating an opening 11-feet tall by 15-feet wide for the safe passage of migrating
salmon and steel head in Neahkahne Creek.
22

SEPTEMBER 2019 | UConOnline.com

The pilot tube procedure provides many of the advantages of
conventional microtunneling for installing small-diameter pipes at
short distances, at significantly lower costs than microtunneling
installations of larger-size pipes.
Unlike conventional microtunneling, a pilot tube method establishes line and grade by installing a small-diameter pilot tube before the
canopy pipe is jacked into place. The hollow pilot tube provides the
optical path for the theodolite (a surveying instrument with a rotating telescope for measuring horizontal and vertical angles) to display
head position and orientation for steering the path of the tube.
For the Manzanita canopy project, LRL mounted an Akkerman
guided boring unit on an American Augers 36/42 600E auger boring
machine with 29,500-foot/pounds of torque and 300 tons of thrust,
supported by a Link Belt 350X3 excavator.
"After initial excavating and moving some 18,000 cubic yards of
material," said Richey, "the canopy system was started roughly 50
feet below Highway 101 in what we called the 'pit' which was 84 feet
wide, 50 feet deep with a 250-foot-long access ramp.
"With the sandy formation in the target area, the decision was
made to build a leveling slab to create a solid, stable platform to set
up the auger boring machine with pilot tube guidance system."
A pilot tube was initially drilled through for line and grade, and
once the correct line and grade were established, the pilot tube
was "chased" by the 36-inch diameter steel pipe and attached to an
exterior grout tube.

http://www.UConOnline.com

Underground Construction - September 2019

Table of Contents for the Digital Edition of Underground Construction - September 2019