Ground Improvement

Geopier Impact® System

History /Background

Geopier Foundation Company developed the Impact System in 2003 to be able to install Geopier elements at sites with a high groundwater table or where soils are susceptible to caving such as foundation soils consisting of loose sands, or soft silts and clays.   By developing the Impact System more projects could take advantage of Geopier technology economically.

Impact Pier Construction Process

The construction process is simple and fast:

  1. Push/vibrate a chained mandrel head into the ground to the desired pier depth.
  2. Fill mandrel and hopper with stone sufficient to build the pier.
  3. Raise the mandrel up to preset distance while discharging stone.
  4. Push/vibrate mandrel down a preset distance minus the planned list thickness to create a compacted lift.
  5. Repeat steps 3 and 4 until pier is complete.

Options

  1. Grout can be added at the start and during the process to create a stiffer and less permeable Impact element.
  2. Concrete can be substituted for stone to create a GeoConcrete™ Column. 

Construction Process-1

How Impact Technology Works

The unique install process displaces soil during installation and utilizes vertical impact ramming energy to construct vertical displacement rammed aggregate pier elements. The cavity is created to full depth by pushing a specially designed chained mandrel head using a relatively large static force augmented by dynamic vibratory impact energy.  The chains allow stone to flow through the mandrel when it is raised up and form a plug to compact the stone when the mandrel is pushed down.  Pier diameters range from 16 to 24 inches in diameter and can be driven to depths of 10 to 60 feet or more depending on the soil conditions and project requirements.

How Impact works-1   How Impact works-2

To create larger diameter piers in soft soils the “L” Mandrel is used.  The larger head creates a larger void through displacement of the soil so a larger diameter pier can be created.   When very stiff soils or debris fill is encountered the “Crown” mandrel is often used to provide higher contact point stresses to push through obstructions or debris.  Alternatively pre-drilling of holes can be performed as needed to penetrate stiff soil layers or obstructions.

L Mandrel   Crown Mandrel

Construction Advantages of Impact Pier Technology

Use in Caving Soils and High Groundwater Conditions – Because the Impact mandrel provides continuous casing of the hole during construction aggregate piers can be installed easily in caving soils and soils below the groundwater table.

No Spoils – The Impact Pier method is a displacement method so in most cases it eliminates/minimizes spoils for sites with Contaminated Soils

Deep Liquefaction Mitigation – Since it can provide deep treatment to densify soils it is excellent for Liquefaction Mitigation

Grouted Impact and GeoConcrete Columns– To achieve higher capacity and stiffness or for environmentally sensitive sites grouted Impact elements or GeoConcrete Columns can be installed with the same Impact Pier Mandrels.

Grouted Impact Pier Elements

Grouted Impact Piers

Grouted Impact elements consist of open graded stone and a neat cement or sand cement grout capable of achieving unconfined compressive strengths up to 6000 psi.

Advantages/Uses

Brownfields projects – eliminate spoils, create an impermeable element so as not to create a conduit for cross contamination of aquifers, and provide high stiffness.

Karst limestone areas – create an impermeable element which will not be a conduit for water flow.

Peat and organic soil layers – ability to span across weak compressible soils which might bulge and cause settlement if piers were built out of aggregate alone.

Increased capacity/stiffness – Grouted Impact elements are 3 to 10 times stiffer than RAP systems.

Avoid stresses on adjacent footings or structures – Grouted Impact elements can be founded on a hard or dense soil layer and transfer the footing stresses down to the hard layer to eliminate stress on adjacent footings or structures.

Utility excavation conflicts – When utility excavations conflict with the influence zone of a footing or Impact element, a grouted Impact element can be designed for this condition.