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Innovative highway embankment system saves time and money in Iowa, Texas

Highway Embankments Article May 16, 2003
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Earthwork contractor Tom Kueter Construction, Peosta, Iowa,
saved the Iowa Department of Transportation (IDOT) $110,000 and a month on the
construction schedule with value engineering.

The $6 million, 7.1-km new alignment of U.S. Highway 30 in
Marshall County near Le Grand, Iowa, would have required excavating 60,000 cu m
and bringing back aggregate and moisture controlled backfill to build
embankments. Two embankments are twin bridge approaches over the Union Pacific
Railroad. A second embankment area brings the road alignment up over a stream
divide where a box culvert is being installed.

Instead of over excavating, Kueter suggested using the
Geopier soil reinforcement system to strengthen the existing soil. According to
Henry Feeken, Geopier Foundation Co. (GFC)-Midwest, West Des Moines, Iowa, the
areas for the embankments were low-lying farm fields and railroad right-of-way.
The combination of soft soils and the weight of the planned 26- to 29-ft-high
embankments would have created a slope stability problem. style="mso-spacerun: yes">

To the layperson, Geopier Rammed Aggregate Piers resemble
underground shafts of aggregate. However, the patented design-build system is a
precise engineered product custom-designed to the site conditions and desired
load-bearing capacity.

To build each pier Peterson Contractors Inc. (PCI) of
Reinbeck, Iowa, the licensed installer, drilled a 30-in. shaft 4 m deep. Then a
modified hydraulic pavement tamper rammed 12-in. lifts of aggregate into the
ground at 1.7 million ft/lb of energy a minute.

The undulating layers of aggregate reinforced the
surrounding soil. PCI's two crews together averaged 100 piers a day while
installing 1,200 piers in three weeks time enabling the project to keep a tight
schedule.

"With the Geopier system, we were able to accomplish
this project safely," added Chris Kueter, president of Tom Kueter
Construction. "We avoided opening a pit next to the railroad and also
manipulated the piers around a fiber-optic cable instead of requiring
relocation."

The cable ran from east to west toward the railroad track.
Shane Van Hauen, PCI project manager, described adjusting the location of about
50 piers to avoid the fiber-optic cable. GFC-Midwest approved the shifted
location of no more than a foot for each pier so stability of the design was
maintained.

Another challenge of the job was an active creek on the
north side of the project since the creek had not yet been rerouted into a box
culvert. The design placed approximately a dozen piers in the creek. According
to Van Hauen, PCI crews drilled the shafts right through the water and the
sides held fine without any cave-ins. "We built those piers with clean
stone," Van Hauen added.

After installation of the Geopier elements in April 2002,
Kueter built embankments ranging from 26 to 29 ft high over the reinforced soil
on each side of the railroad track. Kueter was performing the earthwork for the
new alignment while preparing for the next phase.

The firm also was doing some mainline paving and detour
tie-in so that the highway was set up for the next phase of concrete removal.
Earthwork concluded last fall on
the new 7.1-km stretch of four-lane highway. Cedar Valley Corp., Waterloo,
Iowa, is currently performing the concrete paving.

The highway construction is part of an ongoing multi-decade
improvement of U.S. Highway 30 (the old Lincoln Way) across central Iowa. In
many areas the highway is being upgraded from a two-lane to a four-lane
divided. The upgrade includes rerouting around cities and central business
districts.

A section on soft soils

On Section 15 of Houston's new Westpark Tollway, Geopier
soil reinforcement is supporting two mechanically stabilized earthwall (MSE)
embankments constructed over soft soils. Champagne-Webber Inc. of Houston had
already begun construction on Section 15 when Tricon Precast Inc. of Houston
and its structural firm Robertson & Associates, Weatherford, Texas, turned
in its bearing pressures for the 23-ft-tall MSE walls that lead to an elevated
portion of roadway. When the engineer of record for VandeWehl of Houston
rejected the figures, it became apparent that the existing soils were
unsuitable for both bearing and settlement of the embankments, according to
Wally Burns, Turner Collie & Braden (TC&B).

TC&B considered taking out the poor material and replacing
it with cement stabilized sand, but opening a pit in the restricted
construction area wasn't feasible. Temporary shoring would have been required
for an existing embankment adjacent to the area plus temporary supports would
be needed for a fiber-optic line and an 8-in. gas line. style="mso-spacerun: yes">

TC&B requested that Tolunay-Wong Engineers, the
geotechnical engineer for the engineer of record, provide a better solution.
The geotechnical investigation indicated a compressible layer consisting of 13
ft of clay soils with sand partings underlain by 6 ft of stiff gray clay with
sand pockets and 34 ft of fine sand and silt. Daniel Wong, Ph.D., P.E.,
recommended soil reinforcement to reduce the settlement to a tolerable range
and to increase allowable bearing pressures.

Jim White, Champagne-Webber project manager, solicited bids
from GFC-Houston for its Geopier elements and Hayward Baker for stone column
reinforcement. The owner, Harris County Toll Road Authority (HCTRA), selected
GFC's bid that used approximately half the number of piers compared to the
stone columns and was nearly half the cost at $162,075.

Design Associate Tommy Williamson, GFC-Houston, submitted
the design to TC&B who plotted in the location of the gas line and
fiber-optic line. Then, Williamson refined the design to move the dozen piers
that conflicted with the utilities.

Between Aug. 26 and Sept. 9, PCI installed 395 Geopier
elements with 12- to 18-ft shafts to stabilize the 17,577-sq-ft, 42-ft-wide
main lane embankment and the 3,864-sq-ft, 28-ft-wide Ramp O embankment. The
drilling was hard, according to Bob Menuey, PCI foreman, because the crew
encountered lots of conduit from abandoned utilities, but PCI persevered and
finished the job in 91/2 work days.

White said, "They did a great job, came in, got the
work done and got out without any problems."

Delays such as finding a remedy for the poor soil under the
embankments and waiting on utility relocations put Section 15 behind schedule.
Section 15 started in December 2001, and White expected to complete this work
by the end of April 2003 if construction proceeded without further
complications.

Overall the critical path is on schedule for the planned
opening in the first quarter of 2004, according to Lisa Gonzales, HCTRA
engineering manager. In an era when public works projects often exceed budget
and time schedules, HCTRA has compiled an enviable record in building the first
three sections of the Sam Houston Tollway and Hardy Toll Road. Forty percent of
the 86 construction contracts were completed ahead of schedule; 98% completed
under estimated cost; and 42% completed both ahead of schedule and under
estimated cost.

Over the railroad

In the Houston suburb of Missouri City, Texas, a railroad
crossed the main thoroughfare of Sienna Plantation, dividing the 8,000-acre
master planned development. A bridge over the railroad was a necessity, yet the
limited 160-ft-wide right-of-way was not wide enough to permit a sloped
embankment.

To build the bridge, MSE walls would have to be erected 400
ft long rising up to 32 ft tall. Tolunay-Wong Engineers, Houston, who performed
the geotechnical investigation, predicted the weight of the fill required for
the high MSEs could cause settlement up to 15 in. in the soft soil at the site. style="mso-spacerun: yes">

One solution of preloading the soil and letting it settle to
equilibrium before building the embankments would have taken an estimated nine
to 12 months, much too long for a timely construction schedule. Excavating the
upper 15 ft of soil under the long embankment area and replacing it with
cement-treated soils or other materials would have been prohibitively
expensive.

The Geopier soil reinforcement system to strengthen the
existing soil was the ideal solution, according to Williamson. Wong recommended
the Geopier solution to both reduce the settlement and increase the safety for
slope stability. In November and December 2001, PCI installed 490 piers, each
16 ft long, to reinforce the soil where the MSE walls were to be built.

NBG Constructors Inc., Houston, finished the concrete
prestressed beam bridge Aug. 1, 2002. The 180-ft-long, 90-ft-wide bridge
carries two lanes and sidewalks and can be expanded to four lanes as traffic
increases.

About the author: 
Carder is a freelance writer operating out of Denver, Colo.
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