Most bridge spans on Metra's Rock Island District line were erected more than a century ago, and now an $86.5 million project will replace a portion of 24 of them.

Since the 1890s, when most of the viaducts were constructed, the commuter rail with 68 weekday runs between Chicago and Joliet, Ill., has seen plenty of changes and could see more.

Locomotives are heavier today than their counterparts were in the 19th and 20th centuries, and the Southwest suburbs represent the fastest-growing part of the Chicago metropolitan area. The line averages about 33,100 passengers each weekday.

The project will replace a portion of each of the viaducts between 18th and 60th streets in Chicago, said Donato Brescia, director of construction for Chicago-based Metra.
The replacement will ensure the bridges can withstand heavier loads and provide efficient service.

advertisement

"We are replacing the bridges because of their age," he added. "They have reached the end of their lives."

Metra has a 100-ft.-wide right-of-way, and each viaduct on the north-south segment has a span averaging 72 ft. wide, said Daniel Sieve, project manager for Chicago-based Walsh Construction Co., the general contractor. Some viaducts are wider, such as the Garfield Boulevard span.

The east portions of the spans are being replaced.

Normal train schedules have continued on the line during construction. "Metra's biggest concern is to make sure their trains are on time," Brescia said.

The project will lay the groundwork for further changes. Plans call for the Rock Island's east half to be used as the main rail bed and signals and key infrastructure to be moved to that side. The span's west half, which is the current alignment for rail traffic, is to become the corridor used to provide maintenance.

Another important element of the existing project is that retaining walls are being upgraded on the east side to support the viaducts.

Eight viaducts will also be filled in as part of the project, said Audrey Renteria, Metra media relations specialist.

Traffic counts revealed that fewer than 50 vehicles a day go through the viaducts slated for fill-in. Savings will be realized because the average cost to seal a viaduct is about $500,000, which is approximately $1.5 million less than the average cost to rehab a structure.

"Some of those [existing] bridges have rust breaking off the bottom," Sieve added.
"Others have holes on the bottom."

The Notice to Proceed was issued in February 2003, and the project is expected to finish in November.

Planning is Key

Planning was necessary because the project involves demolition and new construction in a structure-dense urban area.

A "stringent" review was done with the Organization of Underground Construction, the city agency that has replaced the Board of the Underground, Sieve said. The review examined "every" bridge, retaining wall and supportive excavation for design.

The process also identified where utility lines near the project are located so relocations could occur. More than a dozen electrical lines were moved, as well as those for telecommunications, gas and water.

A large number of utilities was placed near the line because existing abutments had already been built when the utilities came through, and it was easy to put them under the adjacent sidewalk. Because of project's time constraints, the construction teams worked to the limits of areas where relocations were to occur to ensure progress was made.

Usually, trenches were dug for new lines, connections were made and old lines removed. On some occasions, discontinued lines were abandoned and covered over.

As preconstruction activities were completed, demolition and new construction could start. Streets were closed so heavy loaders could be brought in to take down old structures, but shoring of the viaduct was usually not needed.

Demolition followed a typical sequence: the ballast was removed, the steel was cut with torches and the abutments' limestone walls were taken down.

A hole was dug in the abutment top to make room for new retaining walls' footings.
Overall, about 19,000 lin. ft. of wall - a figure greater than 3.5 mi. - are expected to be installed.

Approximately 90,000 cu. yds. of embankment was laid to achieve the desired elevation, Sieve said. The minimum clearance under the new span portions will be 13 ft., 6 in.

"We have problems all the time with semitrailers getting trapped under the viaducts," he added. "That's what part of this will eliminate."

The new dirt will also ensure that Metra has enough ground at the desired height to accommodate structure and equipment in its right-of-way.

Cranes with 300 tons of lifting capacity were brought in to reconstruct the crossings.

The heavy lifting capacity was needed to raise the average 72-ft.-long, 8-ft.-tall girders, which from below look like walls. The floor pans and plate deck were placed next.

About 6,750 tons of steel will be used to reconstruct the crossings, Sieve said.

Sub-ballast was laid, and top ballast will be put down in the future. Eventually, track will be laid for the new rail bed.

Designing Walls

Four designs were used for the retaining walls, based on factors that included realizing cost savings when appropriate, the nearness of adjacent properties and varying soil conditions.

"You can't believe how the soil condition changes from north to south," said Walter Rymsza, vice president of Chicago-based Bowman Barrett & Associates, the design engineer.

Around the 18th Street viaduct, for instance, the top layer is composed of sand because the Lake Michigan shoreline had once been west of its present location.
Sand is a problematic soil component because it is weaker than clay.

A system that includes soldier piles was selected for areas with sand and adjacent structures close by, Rymsza said. Because the foundations are drilled, rather than driven, vibrations are fewer than would otherwise be the case. And as a result, nearby structures do not suffer the same impact as they would with other foundations.

A hole was bored, concrete was poured in and steel H-piles were stabbed into the concrete, he said. The concrete cured, and above grade, a precast lagging wall was installed to provide the finish.

"And to provide horizontal stability, I use an anchorage system - another piece of sheeting piling - 60 to 70 ft. away from the wall and then I have rods connecting the two," Rymsza added.

Other wall designs included sheet piling with grouted tiebacks for retention, precast and cast in place. The project took about 140 ft. of cast-in-place wall.

Safety Concerns

Safety was monitored to avoid the possibility of tragedy occurring in areas where trains are moving and people working.

Flaggers were placed at each construction site, and they have contact with train operators. "If the flagger sees there is a situation or if an operator has a concern about what we are doing, the flagger will notify us to swing away," Sieve said.

Looking ahead, new tracks will be placed on the east alignment, signals will be moved, and the switchover of trains will occur in three phases, Metra's Brescia said.