Collins was contacted to perform an underwater inspection of Mars Wrigley riverwall in April 2016. Mars Wrigley maintains a sophisticated corporate R&D facility on Goose Island in the Chicago River in Chicago, Illinois. As Jones Lang LaSalle (JLL), the property manager soon realized, Collins offered a much wider range of engineering services than just underwater inspection.
The underwater inspection report recommended further investigation for two large areas of the riverwall that were leaning out into the river; even above water, the deformations were clearly visible. Consequently, JLL retained Collins for an investigation of the riverwall anchorage system. This was performed by digging test pits behind the steel sheet piling to expose the waler and battered piles. A marine and heavy construction contractor was subcontracted by Collins to provide an excavator and operator for this phase.
Based on the findings of multiple failure modes for the waler-to-battered pile connections, in spite of minimal corrosion, Collins recommended repair or replacement of the entire northern wall. The western wall was a newer construction with more robust anchorage details displaying no signs of distress. Collins was under contract with JLL to design the recommended repairs and presented several preliminary design options, including estimated phased construction costs. Collins prepared detailed plans, specifications, and an estimate based on the final repair option selected by the client. A geotechnical subconsultant performed soil borings to establish the wall design parameters.
While all this was happening, JLL also solicited Collins’ help with non-marine structural issues. An elevated concrete slab system, forming a patio area by the building, experienced some distress as a flush-mounted light fixture collapsed into the voided area when someone accidentally stepped on it. Collins performed two visual inspections and determined that the metal deck below the concrete slab, although galvanized, had corroded significantly and the lip of the deck supporting the light fixture was no longer adequate to support it.
Although the building was only about a dozen years old, the detailing of the elevated concrete patio allowed moisture to be trapped and accelerate the deterioration of the metal deck. Although the design drawings indicated that non-composite metal deck should be used simply as a stay-in-place form for the concrete slab, the actual metal deck that was corroding was of a composite style. Collins recommended limited destructive testing (concrete cores) to verify that the concrete slab was properly reinforced with rebar per the original design. This revealed that the patio slab had been the victim of an undocumented substitution—only temperature and shrinkage steel was present in the concrete, with the composite metal deck being used not only as a form for the wet concrete but for the permanent tensile reinforcement. This caused the rapid corrosion of the reinforcement supporting the patio slabs.
JLL again asked Collins to design a repair, this time for a building element. Collins prepared detailed drawings, specifications, and a cost estimate for the demolition of the existing metal deck/concrete fill patio and replacement with a traditionally reinforced concrete slab.
A permit expediter was subcontracted to assist with the City of Chicago building permit process. Not only was a standard Building Permit required through the Department of Buildings, but also a Harbor Permit, since the patio is within 40 feet of the river.