Geopier Grouted Impact® System

The Grouted Impact® system provides owners and designers with a Rigid Inclusion ground improvement method that both reinforces and stiffens poor soils, and provides some of the benefits of pile foundations —without the drawbacks. It’s an ideal solution when stone alone does not provide enough reinforcement.

This unique Geopier® technology (Rammed Aggregate Pier®) provides a stable bearing layer for spread footing foundations; no special load transfer platform is required.

Geopier Grouted Impact Construction Process

  1. The Geopier Grouted Impact system relies on the same specially designed mandrel and tamper foot as the Impact®system. Cement grout is mixed with the aggregate to create a Rigid Inclusionmethod; this provides engineering benefits in the following circumstances:
    • Cohesive or organic (peat, organic silt) soils with low shear strength where the grout serves to inhibit bulging of the pier into the soft layer.
    • Contaminated soil where the grout creates a low-permeability seepage barrier.
  1. The grout is pumped into the mandrel and introduced within the soil strata where it is needed — the soft cohesive and organic soils where normal ground improvement techniquesare either ineffective, impractical or too costly. Each pier is constructed with heavy downward static force and dynamic vertical ramming. This results in excellent coupling with the surrounding soils and reliable settlement control with superior strength and stiffness.
  2. Following installation, the Geopier Rigid Inclusionelements support standard shallow spread footings, embankments, walls and other structures. The footing stresses are attracted to the stiff RAP elements, resulting in engineered settlement control.
  3. The design has elements of both pile capacity and ground improvement.  Ground Improvement Engineering has successfully designed a number of Geopier Grouted Impact System projects for significant structures in the Midwest.

Geopier Grouted Impact Construction Advantages

  • Significantly stiffer in organic soils and soft clay
  • Clean and rapid installation
  • Can allow for standard spread footings
  • Does not need a load transfer platform beneath foundations
  • Straightforward, understandable design
  • Improves bearing capacity
  • Field-tested

CASE HISTORY: Integrated Science and Engineering Laboratory Facility, St. Cloud State University, Saint Cloud, MN

Project Description:

The ISELF educational building is the biggest part of St. Cloud State University's recent science initiative.  It is a 100,000 square foot, three story structure with a full basement.

The foundation loads ranged from 100 kips to over 1,400 kips on the columns, and 8 to 24 kips per lineal foot on the perimeter strip footings.

Subsurface Conditions:

Braun Intertec Corporation (Braun), the geotechnical engineer, encountered deep fill and organic soils extending up to 28 feet below the basement floor level.  These poor soils were confined to the southern half of the ISELF footprint and were likely a former ravine that had been filled in sometime earlier; Braun found competent sands in the northern half.

Rubble fill was encountered in the southwestern portion during the initial excavation work; the rubble extended about six feet below the basement  level and was removed.


We worked closely with the design and construction team to develop an economical, practical solution. Rather than deep pile foundations with a structural slab, the team decided to support the northern half of the building on the competent native sands, and the southern half with a combination of the Impact System and the Grouted Impact System.  Braun developed the initial demarcation between the 'good' and 'poor' soils, and through pre-drilling this was refined during construction.

The Grouted Impact System was employed for footing support in the buried organic soil areas; the grout mixed with the crushed stone provided resistance to bulging (creep) in the soft organics while still allowing the spread footings that the team desired.

The structural engineer, BKBM Engineers, designed the building foundations as normal strip and column footings sized for an allowable bearing pressure of 4,000 pounds per square foot.  The basement floor was a conventional slab-on-grade.

Foundation Service Corporation, a licensed Geopier technology installer, constructed the Impact and Grouted Impact system elements.

Project Team

Geopier Designer: Ground Improvement Engineering
Structural Engineer:  BKBM Engineers
General Contractor/Construction Manager:  McGough Construction, St. Paul, MN
Geotechnical Engineer:  Braun Intertec Corporation – St. Cloud, MN
Grouted Impact System Installer: Foundation Service Corporation, Hudson, Iowa

Ground Improvement Engineering has used the Geopier Grouted Impact system for many years, including at this university in Minnesota where we encountered deep rubble, likely due to a filled-in ravine. Read our project spotlight.