GEOPIER X1® System

The Geopier X1® system creates Rammed Aggregate Pier® (RAP) elements using a patented vertical ramming process which is a combination of both replacement and displacement methods. It is a good fit for sites that are generally efficiently reinforced with pre-auguring in cohesive and clay soils but marginally unstable. This system is also more effective in much deeper foundation installation depths — easily up to 45 feet.

The RAP elements are constructed by applying direct vertical ramming energy to densely compact successive lifts of high quality crushed rock to form high stiffness engineered elements. The vertical ramming action also increases the lateral stress and improves the soils surrounding the cavity, which results in foundation settlement control and greater bearing pressures for design.

Like the original Geopier systems such as the GP3® System, the X1 system’s drilling operation allows for visible inspection of the hole and the opportunity to address changing ground conditions as they happen. Its performance, flexibility, and cost-effective qualities make it the ideal solution for reinforcing a variety of different soil types. Installation can be much faster when installing hundreds of elements because the compaction chamber remains in the hole throughout the process to introduce aggregate.

Geopier X1 Design/Construction Process

The Geopier X1 system builds replacement/displacement RAP elements to reinforce good to poor or soft soils, allowing for construction flexibility and the ability to build through caving zones that are encountered during drilling operations. RAP solutions are designed to provide superior total and differential settlement control and increased bearing support to meet project requirements.

  1. The process first involves drilling a cavity. Drill depths normally range from about 5 to 40+ feet, depending on design requirements. Pre-drilling allows you to see the soil between the borings, ensuring that the piers are engineered to reinforce the right soils.
  2. Layers of aggregate are then introduced into the drilled cavity in lifts. A patented chamber compaction head allows lifts of aggregate to flow to the bottom of the hole allowing for fast pier construction.
  3. Compaction is achieved through static down force and dynamic vertical ramming from the hammer. The process densifies aggregate vertically and the patented compaction head forces aggregate laterally into cavity sidewalls. This results in excellent coupling for soft soil improvement and reliable settlement control.
  4. Following installation, RAP elements support shallow foundations and floor slabs, reduce liquefaction potential, and improve stability support of embankments, walls and tank pads. The footing stresses are attracted to the stiff RAP elements, resulting in engineered settlement control.

Geopier X1 Applications

Geopier systems have become preferred replacements for massive overexcavation and replacement or deep foundations, including driven piles, drilled shafts or augered cast-in-place piles. Local Geopier engineers and representatives work with you and your specific soil conditions and loads to engineer a project-specific practical solution for ground improvement. With multiple systems, we can engineer support for virtually any soil type and groundwater condition across many applications, including:

  • Foundations
  • Floor Slabs
  • Industrial Facilities
  • Storage Tanks
  • Liquefaction Mitigation
  • MSE Walls/Embankment Support
  • Slope Reinforcement
  • Transportation
  • Wind Turbines
  • Uplift & Lateral Load Resistance


Sanford Imagentics facility in Sioux Falls, South Dakota.

Jeff Christensen, P.E., Senior Engineer with Ground Improvement Engineering in South Dakota, shares a project example on the Sanford Health campus in Sioux Falls, featuring the Geopier X1® replacement Rammed Aggregate Pier® system.

The Sanford Imagenetics facility was completed and opened successfully in 2017, a three-story medical building plus one below grade walk-out. This project is a great example of how ground improvement technology has evolved over the last few years to provide cost-effective solutions to avoid deep foundations.

Medical buildings typically have high load requirements. When you marry that with poor soils, the fun begins. The Sanford campus geology is primarily undocumented existing fill overlying soft lean clay and sandy soils (loess and alluvium) followed by stiff to very stiff lean/fat clay.

During the preliminary pricing phase in 2015, the general contractor reached out to us about cost-effective alternatives to costly deep driven piles. Having worked for this contractor previously and on projects for Sanford Health, we understood the soil conditions and the potential alternatives.

One of the unique features and challenges of this project is that the lower level extends deep within the hillside; the interior “rear” wall acts as a retaining wall resisting high-earth pressures. We needed to control settlements for the resulting wide footing while maintaining an attractive price solution.

These considerations pointed to the Geopier X1 replacement Rammed Aggregate Pier (RAP) system as the alternative to a driven pile solution. With X1 we can install very stiff rammed aggregate elements up to 40 feet below grade. For the Sanford Imagenetics project, our installer built X1 elements up to 30 feet below the foundations.

After excavation to the subgrade elevation, the X1 construction began in earnest. The process involves drilling a cavity and lowering a mandrel with a patented internal compaction mechanism into each cavity. Crushed aggregate is placed into the cavity from above and that material flows into and through the compaction chamber. The mandrel is lifted vertically and then driven down to form compacted lifts. Each layer is vertically rammed and compacted until each RAP element is fully constructed to project specifications.

The Geopier ground improvement was designed to provide differential settlement control and increased bearing pressure for conventional footing support.

Installing hundreds of elements in a few weeks, this solution saved the project hundreds of thousands of dollars in deep pile foundation costs and several days in the schedule.

Patients and staff who enter the Sanford Imagenetics building probably don’t think about the foundation of this facility, and they really don’t have to give it a thought. With the help of improved technologies in our field, Sanford Health redeveloped an older portion of their campus for the future.


A five-story hospital with below-grade level and an adjacent three-story medical building were recently completed for Avera Health in Sioux Falls, South Dakota. Tricky elevations and poor soil conditions created the opportunity to use a ground improvement solution in lieu of deep augercast piles.

The difference in finished floor elevation between the hospital and the medical office building is about 13 feet. This significant elevation difference created some challenges not only with grading/filling the building pads to their respective design subgrade elevations, but also with our approach to installing the reinforcing elements.

We recommended the Geopier X1® replacement Rammed Aggregate Pier® (RAP) system for improved bearing capacity and settlement control. Our approach included installation of RAP elements just beneath the footings of the hospital and the medical building. We also installed elements just outside the hospital lower level’s walls to support grade-raise fills of more than 3 feet. Working with the contractor, we developed a benching or step system to move our equipment gradually from the hospital elevation to the medical clinic elevation. We had to carefully manage installation depths and sometimes navigate around any foundation work happening simultaneously.

Installation occurred prior to construction of the hospital’s foundation walls. The total project lasted about one month and included close to 1,000 elements. The footing stresses are attracted to the stiff RAPs, resulting in engineered settlement control.

RAP elements were not installed beneath the floor slabs of either facility, the parking deck or canopy footings, as this Geopier system was designed for bearing capacity and settlement control only. Ultimately, this ground improvement approach and solution saved tens of thousands of dollars in labor and materials costs.

View our Geopier GP3 system as an additional option using RAP elements.