Ground Improvement

GeoConcrete® Columns

History/Background

Geopier developed the GeoConcrete column system in 2004 in response to the need to provide higher capacity piers for projects with larger area fills and adjacent footing stress concerns.  GCCs consist of an unreinforced concrete column with a bottom bulb and a top bulb to transfer high footing or embankment stresses down to a dense or hard soil layer.

GCCs 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 with concrete.
  3. Raise the mandrel up to preset distance while keeping a constant head of concrete.
  4. Push/Vibrate mandrel down a preset distance minus the planned lift thickness to create a compacted lift or bottom bulb.
  5. Repeat steps 3 and 4 until an adequate bottom bulb is created.
  6. After bulb is created pull mandrel up while keeping concrete under pressure.

Option – An enlarged head can be provided to lower the stress transferred on to the footing pad or load transfer platform.

How GCCs Work

Geopier GCCs are designed to control foundation settlements by transferring the stress from a footing or embankment down to a stiffer or harder layer.  The stress is transferred through the use of a granular pad or load transfer platform specifically designed for the project conditions.  Settlements are estimated by summing the estimated settlement for each of the layers within the three layer system:

  1. Engineered granular pad.
  2. GCC reinforced zone (the “upper zone”).
  3. Zone of soil below the bottom of the GCC elements (the “lower zone”).

The GCC elements are also checked to verify that they meet design requirements for structural integrity.

How GCC Works    How GCC Works-2

Case Study: 11th Street Bridges, Washington, D.C. 

Geopier GeoConcrete columns have high capacity and have been tested up to 700 kips using Statnamic Testing.  For the 11th Street Bridge project, the results of 5 Statnamic tests showed an ultimate capacity of approximately 700 kips with 1.2 inches of displacement.

Statnamic Load-1 Statnamic Load-2

Construction Advantages of GCCs

Advantages/Uses

  • Brownfields Projects – GCCs eliminate spoils, create an impermeable element so a conduit for cross contamination of aquifers is not formed while also providing high stiffness and capacity.
  • High Embankment Loads/Load Transfer Platforms – Due to the high capacity of a GCC and the ability to create a large head GCCs can have a relatively wide spacing to optimize capacity, yet can minimize the load transfer platform thickness by creating a large diameter head to spread out the load.

GCC Advantages-1    GCC Advantages-2

  • Karst Limestone Areas GCCs create an impermeable element which will not be a conduit for water flow.
  • Peat and Organic Soil Layers – GCCs provide the ability to span across weak compressible layers which might bulge and cause settlement if piers were built out of aggregate alone.
  • Increased Capacity – GCCs have a high design capacity up to 4 times higher than typical aggregate piers.
  •  Avoid Stresses on Adjacent Footings or Structures – GCCs 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.