Trotter and Associates, Inc works with Michels Corporation to install Grouted Rammed Aggregate Piers utilized during the design and construction of the DuPage County Public Works Nordic Park Wastewater Treatment Plant Rehabilitation located in Itasca, IL. As part of the design process, aggregate piers were selected as a cost-saving foundation for two Tertiary Clarifiers and a RAS/WAS Pump Station due to the presence of an organic clay layer beneath the proposed mat foundation. This technology modifies the surrounding soil, increases bearing capacity and reduces settlement.

Other options considered by the design team but ultimately were not utilized included undercutting the unsuitable soils layer, installation of steel pipes, and helical piles. The approximate 4,600 square-foot area required a total of 104 30-inch diameter aggregate columns to be installed to an approximate depth twenty-two feet below grade. After installation, load testing was completed to ensure the required capacities were met.



The process of installing the pier included using a thirty-inch diameter auger to predrill the proposed pier locations. Upon completion of the pre-drill, a depth vibrator was inserted into the hole. Aggregate and grout were fed into the hydraulic vibrator through a hopper and hose where it was compacted to densify the soil. The material was then inserted to construct the aggregate piers creating the grouted aggregate pier foundations for the two clarifiers and pump station. This method of construction is efficient, and all 104 piers were installed within 6 days.

To see a video showing the process, please click on the following link: https://youtu.be/U6KYaJwK_u4