Directly below Millennium Park is an existing 2186 car underground parking structure. In order to keep this existing parking structure safe and operational the lightweight geofoam was used in place of soil to reduce weight which then allowed the additional weight of the park structures and related park facilities.
Geofoam was also used to create landscape features around the park which helped the designers create the look they wanted while achieving the proper water drainage for the overall site plan. An additional advantage was that construction could be completed in various weather conditions, including the harsh Chicago winter.
ACH Foam Technologies