||A complex 400,000 SF 4-story retail podium above grade sitting atop a 340,000 SF 4-level below grade transportation center and parking structure in the heart of downtown Chicago. A unique top down method of construction was utilized where the above ground portion was being erected while the underground structure was being mined. This dense downtown urban site with highly trafficked roadways, underground subway systems and an underground pedestrian walkway required extensive coordination with City regulatory agencies including vibration control monitoring. The foundations and retail podium structure were built for future construction expansion of 2 high-rise towers. In addition, 4 different types of deep foundation support systems including a perimeter slurry wall were utilized.