Project Overview
The third and final phase
of the Chicago Riverwalk construction project was recently opened to the public
on October 22, 2016. This final phase extended the Riverwalk, located on the
South side of the main branch of the Chicago river adjacent to Wacker Drive,
from LaSalle Street to Lake Street putting the final leg on a continuous
walkway from the heart of downtown to the lakefront.
In order to
create a continuous path, the project required a means for pedestrians to pass
under the bridges. Originally, the user's path would be impeded once they’d
reach a bridge at which point they’d have to use stairs to exit, cross the
street, and re-access on the other side. The Riverwalk project alleviated
this issue by including an underbridge concrete path which spans over
submerged piles within the existing river’s right of way.
Precast Solution
Utility Concrete Products was brought on
to fabricate and supply the main precast structure for these paths, referred
to as underbridge tubs. Each underbridge required three precast sections,
which resemble a concrete bathtub, to provide the necessary structure to pour
cast-in-place (CIP) concrete and create a composite connection to complete
the underbridge. The tubs are 10’ wide x 4’ tall and varied in length from
38’ up to 86’-3 ¾” with the heaviest piece being at the LaSalle St. Bridge
weighing in at nearly 164,000#. The longest tubs were poured with a precise
camber that leveled out once the CIP concrete was poured within. Poured with
a High Strength High Performance Concrete (HSHPC) mix, the tubs are designed
to withstand the marine elements as they are constantly submerged in the
Chicago River.
Each tub is heavily reinforced with large diameter
epoxy coated rebar spanning the longitudinal direction, and was cast with
either 6’ or 8’ diameter openings in the floor so that they could be
installed on similar size piers in the field. In these openings are massive
½” steel embed plates to connect to the piers. Further, a post installed
neoprene seal provided a watertight seal between the precast and shafts once
installed.
To transport the precast tubs to the jobsite, they were
delivered to an auxiliary site along the river and loaded onto specially
designed barges with the largest capacity crane in the Chicagoland area.
Once loaded onto the barges, the tub sections were welded together and
floated up the South Branch of the Chicago River to the jobsite. The barges
positioned the tubs over previously drilled piers that they set on prior to
being lowered to final elevation by a complex jacking system. Once in
place, the tubs were heavily reinforced and infilled with the HSHPC mix,
which secured the tubs to the piers below and also created the final
walking surface for the users. Each underbridge was ultimately outfitted
with a guardrail and a stainless steel canopy system to shield from runoff
of the bridge decks above. UCP is grateful to have been a part of such a
high profile project for the City of Chicago. |