Pharma Tank Farm Case Study

Read how the ground improvement solutions provided by CNC Foundations helped a partner save money before they installed large storage tanks.

Ground Improvement—Installing Vibratory Stone Columns / Aggregate Piers

The Opportunity

The construction of two large bioreactor tanks and one emergency water tank was a planned expansion for a pharmaceutical facility. All three tanks required a bearing pressure of 3,750 pounds per square foot. The foundation below the tanks featured varying strengths, causing settlement concerns that would impact the project’s long-term success. The biggest concern was excessive differential settlement of the soil that could cause the tanks to tilt.

The Solution

CNC Foundations determined that aggregate piers/vibratory stone columns (VSCs) would be the best ground improvement solution. It took approximately 500 stone columns going 30 feet below the grade to reduce total settlements and control the differential settlement. Our design/build team made sure the tanks would perform as intended for the long term and that no mechanical issues would develop in the future due to settlement.

Key parts of the installation included pre-drilling multiple holes in the soil to guarantee that the columns would reach the targeted depths. We had a 36-inch Load Transfer Platform design for the area between the top of the pier and the bottom of the tank. Lastly, as part of our Quality Assurance process, we perform two load tests after installation to make sure the Aggregate Piers/Vibratory Stone Columns were up to standards and acceptable to our Third Party Design Engineer.

The Results

CNC Foundations worked directly with the site owner for over a year to finalize a cost-effective ground improvement solution against our foundation options. Our design for improving bearing pressure underneath the tanks allowed for reduction of the footprint, saving our partner money on concrete foundation cost and time.

Project Details


Vibratory Stone Columns

Bearing Capacity / Settlement Control

Differential Settlement FAQ

What Is Differential Settlement?

Differential settlement is when a building’s foundation settles unevenly. If the right side moves three inches and the left side moves two inches, there’s a one-inch differential settlement, which causes the structure to tilt.

How Do VSCs Prevent Differential Settlement?

VSCs stiffen up the soil matrix and reinforce existing soils to reduce compressibility. Engineers can even reduce the effects of earthquake vibration by installing VSCs in a grid pattern.

What Are the Causes of Differential Settlement?

Various issues cause differential settlement, including:

Weak Bearing Capacity

Soils that are weak and highly compressible can cause settlement issues. Reputable foundation companies can identify and solve this problem before construction.

Poorly Compacted Soil

Building sites often consist of land that was artificially leveled and filled. The soil provides a solid foundation when properly compacted, but becomes uneven when it doesn’t.


Seismic activity and nearby road traffic cause the soil to settle unevenly, leading to structural damage to a building.

Not sure what geotechnical solution can work for your job? We can help.

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