VIBRO-REPLACEMENT – STONE COLUMNS (VR)

TECHNIQUE:

Stone columns are formed by inserting a vibratory probe to incorporate granular material into the ground and create vertical inclusions with high stiffness, shear strength and draining characteristics.

Two types of feeding process (top or bottom) are used with either air (dry method) or water (Wet method) jetting fluids. Under uniformly loaded structures such as embankments and slabs-on-grade, stone columns are installed on regular grid spacing. In this case, a load transfer platform is designed and installed between the top of the columns and the structure. The stone columns installation results in a significant reduction of the total and differential settlements. Stone columns can also be installed as a group to support isolated loads (i.e., shallow foundations) or directly under linear loadings such as strip footing or retaining walls. In this case, stone columns increase the bearing capacity of the soil while reducing the magnitude of settlement.

This technique is well suited for the improvement of soft to very soft soils (Silty Sand, Clays, Silts and heterogeneous Fill), However, when the surrounding soil present a risk of long term degradation of their geotechnical characteristics (organic soils, very soft clays, peat..) with very limited lateral confinement, stone columns should not be used for settlement reduction or bearing capacity improvement.

ADVANTAGES:

  • Reduce settlements of compressible soil layers, their draining characteristics result in an increase in the time rate of consolidation settlement in soft cohesive soil.
  • Because they are made of compacted granular material, no curing period is necessary and no cut-off to the shallow footing grades are required as the excavation of the footing can immediately follow the installation of the stone columns down to the required elevation.
  • High production rates
  • Well-adapted to the mitigation of liquefaction potential thanks to the combined effect/ advantage of their draining potential and the increase of shear strength and stiffness of the improved soils.