Rock Island Police Department

Installing Vibratory Concrete Columns

Ground Improvement – Installing Concrete Columns


The City of Rock Island proposed to build a new Police Department. The main building at the new facility is L-shaped with a short leg.


Geotechnical borings indicated the site consisted of uncontrolled fill ranging from three to eight feet throughout the site. Below the fill is a layer of organics with high moisture contents above 200 percent and N-values from 1 to 5 blows per foot. This layer of organics ranged from 5 to 10 feet throughout the site.

The initial recommendation from the design team was to install aggregate piers to improve the soils to 3,500 psf with less than 1″ total settlement and ½” differential settlement.

According the FHWA guidelines, the thick layer of organics posed a problem as aggregate piers are not a viable solution when encountering organic soils with high moisture content.

Because organics with high moisture content release their pour water pressure much slower than typical soils – even with the installation of aggregate piers – settlement would continue for an extended period of time.


In considering the organic layer, CNC Foundations’ engineers designed a Vibratory Concrete Column system that could penetrate the organic layer, improve the project site to the appropriate 3,500 psf, and limit the settlement to the design requirements.

Testing in the field validated the design. The crew finished the project a week ahead of schedule.

Project Details

Police Department

Rock Island, Iowa

Ground Improvement, Vibratory Concrete Columns

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

Related Case Studies

Ground Improvement

Government Housing Facility

A government housing authority added two, four story concrete buildings connected by a sky walk, totaling approximately 25,500 sq ft.

View Case Study

Aggregate Piers & VCCs

Scott Air Force Base, IL | VCCs

A new, six-story, 169,000 sq ft Visiting Quarters was planned for Scott Air Force Base. CNC Foundation’s design worked exactly as expected.

View Case Study

Vibratory Stone Columns


At a 21,000 sf historic library near the Kansas River. We installed vibratory stone columns for ground improvement.

View Case Study

Let’s Talk