Installing Vibratory Stone Columns
Ground Improvement – Installing Vibratory Stone Columns
For this project, we designed and installed a design-build system of Aggregate Piers/Vibratory Stone Columns (VSC) to support the Bioreactor A tank, Bioreactor B tank, and the Emergency Tank. Criteria for the project was 3,750 psf bearing pressure for the reactor tanks and 2,000 psf bearing pressure for the emergency tank. Total settlement was estimated at three inches due to variability in soil conditions across the Bioreactor Tank areas.
REQUIREMENTS AND CHALLENGES
For a successful installation, this project required the design of the aggregate piers to include a high concentration of VSCs across the tank’s location, to ensure both total and differential settlements were controlled. This concentration of VSCs, and the density of the soil, required a custom approach to the VSC installation to reduce spoils, and ensure the VSCs reached their intended depth.
This project’s initial difficulties were centered on the COVID-19 pandemic. The Novozymes team, outside engineers, and ourselves were learning to cope with a new reality. No site visits, remote work environments and distractions, as well as changes to everyday life.
Once on site, we discovered a three (3) foot layer of gravel was installed as the working pad cap. This was not taken into the pre-bid design and had to be taken into our approved design. The respective engineering teams worked together to come up with a solution that left the piers stopping at the lower level of the gravel layer and added compacted gravel to each location to bring it up to installation grade.
SOLUTION AND RESULTS
At the site, CNC Foundations performed layout for nearly 500 Aggregate Piers/Vibratory Stone Columns across the three tank locations. Due to the variability of the soil, including dense layers, we utilized our pre-drilled, bottom feed method of installation. All Aggregate Piers/Vibratory Stone Columns were installed to a nominal 24-inch diameter and were installed to depths of approximately 25 to 30 feet below installation elevation at the tank locations.
There were some specific components that made our installation successful. One was the use of our Quality Assurance/Quality Control that we employ on each site we install aggregate piers/vibratory stone columns. Our third-party design firm will retain our design by meeting the project criteria, they mandate and confirm testing results, and installation in compliance with their design. Another large differentiator is CNC Foundations’ On‐Board Computer System which is utilized to monitor the installation of the piers /columns. This provides real time data to the operator allowing him to monitor the density of the pier / column as it is installed. This provides a “receipt” of sorts for each pier that we can give to the client.
Finally, Full‐Scale Load Testing was performed to verify the capacity of the piers/columns. This test was performed on a sacrificial pier and foundation was loaded to the weight and time as directed by the design engineer. The tanks were loaded in 25% increments, and a water test was performed after full loading for one month, to ensure long term performance. Post water test settlements were estimated as 1.5 inches total and 1 inch differential.
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