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Geopier GP3 - Drill and Fill Rammed Aggregate Pier

The Geopier® GP3 system uses replacement Rammed Aggregate Pier® (RAP) elements to reinforce good to poor soils, including soft to stiff clay and silt, loose to dense sand, organic silt and peat, and variable uncontrolled fill.  The unique installation process utilizes pre-augering and vertical impact ramming energy to construct RAP elements, which exhibit unsurpassed strength and stiffness.  RAP solutions are designed to provide superior total and differential settlement control and increased bearing support to meet the project requirements.

Construction Process
 
  1. ​Drill a cavity to depths ranging from 7 to 30 feet deep and 24-30 inches in diameter.
  2. Place a 24-inch layer of open-grade aggregate at the bottom of the cavity.
  3. Compact the aggregate using a patented tamper that delivers a high-energy impact ramming action.  The ramming action compacts the aggregate and pre-stesses the surrounding soil.  Successive lifts of well-graded aggregate are then rammed in place.
How Geopier Works
 
The high-energy compaction process produces significant lateral pre-straining and pre-stressing of the adjacent matrix soils so much that the lateral stress in the soil surrounding the Geopier element approaches, Kp, the coefficient of passive earth pressure.  This means that the lateral stresses of the soil on the Geopier element can be as much as 2 to 3 times greater than originally imparted by the soil.
rammed aggregate pier
how geopier works

Stiffness - When a vertical column load is imposed on the GP3 element, it is the lateral stress that build up in the soil that provides confinement to the GP3 element making it stiffer and able to resist lateral movement and bulging.  It is this high stiffness that allows a Geopier supported foundatioin to control settlement to very close tolerances.

 

Skin Friction - It is also the same lateral stress that provides excellent coupling of the GP3 element with the soil so that vertical loads can be shed into the soil efficiently.  In many applications, the elements shed the entire vertical load over the length of the pier such that the vertical stress at the bottom of the pier is zero.  This has been confirmed by load cell instrumentation of GP3 elements. 

Settlement Control - Where footing stresses are the highest, GP3 elements provide the needed stiffness.  For a rigid footing the stresses are highest on the soil in the zone directly under the footing as well as a depth of 1 to 2 times the footing width.  GP3 elements control settlement by providing a very stiff element that will attract stress away from soft soil or variable loose fill material to a depth needed to control settlement and minmize settlement of the soils below it.

Applications for Geopier Technology
 
Geopier was originally developed for the support of shallow foundations as an alternative to costly, massive over-excavation and recompaction.  Over the past decade, Rammed Aggregate Pier (RAP) systems have most often been used as a replacement for costly deep foundations (driven piles and drilled piers), and in the following applications:
 

  • Building Foundations

  • MSE walls & embankment support

  • Slope stabilization and landslide repairs

  • Floor slab support

  • Tank support

  • Liquefaction mitigation

  • Uplift control

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