By: Carol Carder, Contributing Author
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.
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.
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.
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.
