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Confusion Hill Realignment Project Nearly Complete

Thu September 24, 2009 - West Edition
Erik Pisor

For more than a decade, a portion of Route 101 in Mendocino County, Calif., has experienced regular winter road delays due to landslides and slipouts.

These often five-hour plus delays have affected travelers and the transportation of goods and services into the area.

The landslides also have caused multiple-day road closures, which from 1997 to 2006 resulted in more than $33 million in maintenance and restoration expenses to Caltrans.

This winter however, delays and closures along the portion of Route 101 known as Confusion Hill will be a thing of the past, as the $65 million Confusion Hill Roadway Realignment Project is nearly complete.

The project involved relocating approximately 1.5 mi. (2.4 km) of Route 101 by constructing a 255-ft. (77 m) tall, three span, cast-in-place segmental bridge; and a 142-ft. (43 m) tall, three span, cast-in-place concrete box girder bridge above the Eel River, according to Evan Paine, project manager for Sacramento-based MCM construction.

Construction of a short section of new highway, which involved an approximately 400,000 cu. yds. (305,800 cu m) rock cut and the installation of two steel soldier pile retaining walls, also was part of the Federal Highway Administration-funded project that began in June 2006.

However it was the bridgework that set the project apart.

“Each bridge has a unique design due to time and cost restraints placed on project development,” said Phil Frisbie, public information officer for Caltrans District 1.

The south, segmental bridge has 30-degree slant legs that allowed the foundations to stay above the 100-year flood plain and reduced environmental permit requirements.

“The segmental bridge is only the sixth of its kind built in California,” Paine said.

Sloping piers, are a feature of the north, box girder bridge, which because of steep and rugged site access required an 80-ft. (24 m) high, 300-ft. (91 m) long work trestle to construct.

The main cranes utilized by MCM for the bridgework included a Maintowoc 4000, a Maintowoc 3900, a Link-Belt LS-518 and a Link-Belt LS-338, according to Paine, who added a pair of self-launching travelers were used during construction of the south, segmental bridge.

All the crane equipment was owned by MCM, who was selected based on being the lowest qualified bidder.

The three-span, south segmental bridge has a main span of 571 ft. (174 m) and end spans of 348 and 436 ft. (106 and 132 m). The structure depth varies from 31.5 ft. (9.6 m) at the piers to 11.5 ft. (3.5 m) at the midspans and abutments, Paine said.

The bridge is comprised of more than 15,000 cu. yds. (11,470 cu m) of concrete, some of which is high, early strength concrete, and nearly 5 million lbs. (2.2 million kg) of reinforcement.

The foundations consist of 11 piles, each 5 ft. (1.5 m) in diameter and approximately 100 ft. (30.5 m) long, at each of the two piers. At each of the abutments are 16-in. (40 cm) diameter piles.

During bridge pours a concrete delivery system pumped concrete approximately 255 vertical ft. (77 m) and another 285 horizontal ft. (86 m) at the extreme lengths, Paine said, adding a mobile concrete batchplant was located onsite.

The pile caps at the bridge’s pier footings are nearly 50 by 36 ft. (15 by 10.9 m) and 10.5 ft. (3.2 m) deep.

The architectural piers are nearly 25 by 19 ft. (7.6 by 5.8 m) at the base, but vary as they stair step in at two locations.

The majority of the bridge’s deck is on a 5 percent incline with a 2 percent cross slope, according to Paine, who said at the peak of construction MCM had more than 60 employees working onsite.

As of July 7 of this year, southbound traffic began using the new segmental bridge and new alignment, according to Frisbie.

The northbound, three-span, box girder bridge has a main span of 229.3 ft. (69.8 m), end spans of 175.8 ft. (53.5 m) and was open for commuter use in late August.

More than 4,400 cu. yds. (3,360 m) of concrete and more than 1.5 million lbs. (700,000 kg) of reinforcement comprise the bridge.

The piers of the bridge were sloped 30 degrees from vertical and varied in dimensions from about 17 by 7 ft. (5 by 2.1 m), at the base, to about 17 by 14 ft. (5 by 4.2 m) at the top of the pier, Paine said.

Because of the slope and the bridge curvature, the pier was trapezoidal rather than rectangular.

Aside from bridge construction, a thru cut that removed of more than 400,000 cu. yds of rock and soil was required in order to construct a new portion of highway.

Blasting also was required to make way for the new highway realignment.

During the thru cut and blasting, Cat 735 trucks hauled rock and soil across the completed north bridge.

The Cat 735s were either rented or owned by subcontractor Ladd and Associates, who was responsible for structure excavation/backfill and roadway rock excavation, Paine said.

Construction of the new highway also included the installation of two, steel soldier pile retaining walls with tieback anchors.

The first wall is nearly 375 ft. (114 m) long and varies in lagging height, which reached as high as 20 ft. (6 m).

The wall includes more than 300 ft. (91 m) of wide flange soldier pile and 43 tiebacks, and received an architectural surface resembling rock formations.

The second wall is 504 ft. (153 m) long and has a lagging height of up to 40 ft. (12 m).

This wall contains 62 wide flange soldier piles, with a combined length of 3,100 ft. (944 m), and utilized concrete whalers to anchor each of the 77 tiebacks.

At the point where the existing Route 101 meets new the alignment, MCM and Caltrans used nearly 3,748 tons (3,400 t) of shredded tires to raise the old highway to the height of the newly constructed highway.

Known as tire derived aggregate, the recycled material is about half the weight per cubic foot of rocky soil and has a lower cost than other lightweight alternatives, such as expanded polystyrene blocks.

The lower weight allowed the large arched culvert below the highway to handle the added road height without reinforcement.

Reinforcing the culvert would have increased the project cost, and increased the development time, which would have delayed the start of construction, according to a Caltrans release.

Because the project site was in a remote area and involved the construction of 1.5 mi. (2.4 km) of new bridges and roadways, the project had little impact on the surrounding community.

All aspects of the realignment project will be complete by the middle of October, Paine said.

Besides Ladd & Associates, other subcontractors on the project included: CMC Fontana Steel, furnish/place reinforcement; Schwager Davis Inc, prestressing; Mercer Fraser, furnish concrete, base, and AC paving; Drill Tec, soldier pile walls; Pacific Coast Drillers, bridge CIDH piles; Finley Engineering Group, segmental construction engineering; Roadway Electrical Works, underground and bridge electrical and seismic; Apex Fence Company, metal beam guard rail installation and removal; and Traffic Solutions, striping and rumble strips. CEG

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