Editing Chicago flood (section)

==Cause==
[[File:Kinzie Street bridge 20100731.jpg|thumb|right|Kinzie Street Bridge]]
Rehabilitation work on the [[Kinzie Street Bridge]]<!--not the railroad bridge--> crossing the Chicago River required new pilings. However, when the City of Chicago specified that the old pilings be extracted and replaced by the new ones, the [[Great Lakes Dredge and Dock Company]] reported back that the old pilings were too close to the [[bridge tender's house]], preventing proper removal without risking damaging or destroying the house. The City of Chicago then gave permission to install the new pilings {{convert|3.5|ft|m}} south of the old pilings. The crew members who began work at the site did not know that beneath the river was an abandoned [[Chicago Tunnel Company]] (CTC) tunnel that had been used in the early 20th century to transport coal and goods. One of the pilings on the east bank was driven into the bottom of the river alongside the north wall of the old tunnel. The pilings did not punch through the tunnel wall, but clay soil displaced by the piling eventually breached the wall, allowing sediment and water to seep into the tunnel. After some weeks, most of the clay between the water and the breach had liquefied, which rapidly increased the rate of flooding in the tunnel. The situation became problematic because the flood doors had been removed from the old tunnels after they fell into disuse.