When the river pilings at Kinzie Street were installed they were just bundles of chain-bound logs-obscure maritime accessories designed to keep errant river pilots from bumping into the base of a bridge.
The pilings are now the most notorious lumber in the city`s history, central to the tale of bungled construction and slothful city workers which have been blamed for causing the disastrous flooding of Chicago`s downtown.
But precisely how last year`s installation of pilings at Kinzie Street punctured the underground freight tunnel system and flooded the Loop is only now unfolding.
While Mayor Richard Daley and others have offered conflicting theories about how Great Lakes Dredge & Dock Corp.`s pilings construction may have breached the tunnel, an expert examination for the Tribune of city engineering records and maps offers the first detailed analysis of how the disaster may have hinged on a mere 12 inches.
Construction workers and city inspectors agreed to deviate from a city contract and move the site of the pilings.
According to an independent engineer who studied records documenting the project and a detailed map of the underground tunnel at Kinzie Street, it was that decision to move the piling cluster just three feet south that caused at least one of the 50-foot-long timbers to be pounded through the wall of the tunnel.
Experts now say the piling was moved a foot too far.
”If driven as originally planned, there would have been two feet clearance between the pilings and the tunnel wall,” said George Kennedy, president of Chicago`s George A. Kennedy & Associates, an engineering firm.
”They had two feet to spare; but when they moved them three feet south, they were driven right into the tunnel.”
Kennedy contends the contractors may have had some room for movement without risking damage to the tunnels. But sinking the pilings three feet from the original site would have placed at least one of the timbers in the cluster on a collision course with the 7.8-foot wide concrete tube, Kennedy said.
Moving the pilings only two feet ”would not have been great,” said Kennedy, ”but it`s better than being stabbed.”
Kennedy, an engineer whose company has consulted on projects ranging from the NBC Tower to the new Comiskey Park, based his conclusions about the tunnel collapse on a review of detailed city underground maps, technical drawings and information publicly released by Great Lakes after the flood.
Great Lakes declined to discuss Kennedy`s findings last week. In earlier statements, officials of the Oak Brook-based marine construction giant acknowledged changing the site of the pilings but said a company investigation determined it did not breach the tunnel wall.
”The investigation to date indicates that the pilings driven into the Chicago River at Kinzie Street never pierced the tunnel,” Witt Barlow, president and chief executive officer of Great Lakes, said at a news conference the week of the flood.
”Based on our review of photographs taken by the city from inside the tunnel before the flood, all piles that were driven near the tunnel were completely outside the tunnel structure. In fact, all but one of the piles in the photograph were quite old and were installed years ago. The company is uncertain at this time when the one remaining pile was driven.”
That one pile, visible in city photographs, is a yellow timber that Barlow described as ”similar” to the southern pine logs Great Lakes pounded into the riverbed during construction of the new piling clusters last summer. In May 1991, Great Lakes received a $335,640 city contract to replace pilings at five locations along the Chicago River. The old pilings were rotted and broken stacks, which had been sunk at the bridges decades earlier.
The 55-foot heartwood logs were installed by Great Lakes and then cut to 50 feet, as called for in city specifications. The contract called for each of the 37 timbers in the hexagonal clusters to be pounded into the riverbed by a barge-mounted pile driver.
An authority on maritime construction said that the 6,000 pounds of force needed to hammer pilings is enough to pierce masonry walls.
”You would have no idea you hit something,” said Karl Luedtke, chairman of the American Association of Small Dredging and Marina Companies and a maritime builder in Frankfort, Mich.
The pilings construction at Kinzie Street, the last of Great Lakes` five projects for the city, began on Aug. 27, 1991. It proceeded routinely, with Great Lakes workers removing and replacing three piling clusters at the northeast corner of the bridge, according to diaries kept by city inspectors who oversaw the project.
The firm on Sept. 10 then moved its construction barge to the bridge`s southeast corner, where the replacement of the last two deteriorated clusters was to begin.
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The next day, company engineers told city inspectors that they believed it was hazardous to replace the two clusters in the location dictated under the contract, according to an inspector`s report. One cluster was located near the path of river traffic; a second was considered too close to a bridge tender`s shack built after the original pilings were installed, records show. Great Lakes engineers feared that a barge collision would send the second cluster crashing into the bridgehouse, company and city officials have said.
Because of the company`s concerns, city workers gave oral permission to change the locations called for in the contract. The first pile cluster, also in close proximity to the tunnel, was installed three to five feet southeast of the old cluster in the waterway, according to city and company officials.
The second new cluster, located near the bridgehouse, was placed three feet south of the old pilings, city and company officials said.
City officials have charged that Great Lakes did not ”remove all existing pile clusters” as called for in the contract.
Great Lakes has said there was a ”forest of old piling stubs” beneath the bridge base and that they removed those specified by their contract.
The two sides agree, however, that city public works employees gave oral approval to relocate the new clusters to the sites proposed by Great Lakes. Daley has fired one worker and recommended suspension of another linked to this approval.
Great Lakes has acknowledged that it did not consult detailed underground maps in advance of the construction project, but charged that the city erred in not informing them about the tunnel. Barlow said his company wouldn`t have taken the job if he had known of the tunnel`s proximity to the construction site.
Using surveys of the area by the Army Corps of Engineers, which did not show the entire tunnel system, the company concluded there were no underground utilities beneath the construction site.
Kennedy, the private engineer, examined the pilings installation using maps obtained from the city`s Board of Underground, as well as the city`s renderings of the completed project.
Great Lakes crews left 10 feet of the 50-foot long timbers above the water line to protect the bridge, according to the city and the company. The Chicago River at Kinzie Street is 21 feet deep, city maps show, which meant that the timbers were driven 19 feet into the riverbed, beneath what is known as the ”mud line.”
The tunnel was 15 feet below the mud line, Board of Underground maps show. Great Lakes has said its pilings are not responsible for breaching the tunnel, but Kennedy maintains that based on city maps showing the new location of the pilings, a four-foot section of at least one pile would have broken through the tunnel wall.
If such a breach occurred, it would not necessarily have caused an immediate deluge, Luedtke said.
Compression caused by new pilings combined with existing pressure from old pilings still embedded in the river bottom would have created what engineers call ”pressure bulbs”-areas of compacted soil around the base of the pilings.
Barlow has said there is a ”forest” of old pilings in the river bottom near Kinzie Street, and a company attorney has suggested that those old timbers could have been responsible for the break in the tunnel.
Even if the tunnel was breached, said Luedtke, the pressure bulbs, combined with the self-sealing properties of the clay soil, could have created a temporary plug.
”When people plug a leak, they use clay (because) it`s impervious,”
Luedtke said. ”Water would take quite a time to leak through. Some of the soil would fall into the tunnel, there would be a little water and then it would be partially sealed by the clay.”
Because of the natural sealing process, Luedtke said, months could pass before a natural plug would give way, unleashing a flood.
”During that time, water could travel down the side of the pilings and into the cracks,” said Luedtke. ”Finally, once the water starts to flow, it just goes-like a dam or a dike.”