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Vibro-Replacement Stone Columns

Vibro-Replacement Stone Columns extends the range of soils that can be improved by vibratory techniques to include cohesive soils. Densification and/or reinforcement of the soil with compacted granular columns or “stone columns” is accomplished by either top-feed or the bottom-feed method.

Cohesive, mixed and layered soils generally do not densify easily when subjected to vibration alone. The Vibro-Replacement Stone Column technique was developed specifically for these soils, effectively extending the range of soil types that can be improved with the deep vibratory process. With Vibro-Replacement Stone Columns, columns of dense, crushed stone are designed to increase bearing capacity, reduce settlement, aid densification and mitigate the potential for liquefaction, and improve shear resistance.


The Vibro-Replacement Stone Column Process
  • Reduces foundation settlement
  • Increases bearing capacity, allowing reduction in footing size
  • Mitigates liquefaction potential
  • Provides slope stabilization
  • Permits construction on fills
  • Permits shallow footing construction
  • Prevents earthquake-induced lateral spreading
Stone Column Construction
The two primary methods of Vibro Stone Column construction are:

 

Wet, Top Feed Method (Replacement and Displacement)
In this technique, jetting water is used to remove soft material, stabilize the probe hole, and ensure that the stone backfill reaches the tip of the vibrator. This is the most commonly used and most cost-efficient of the deep vibratory methods. However, handling of the spoil generated by the process may make this method more difficult to use on confined sites or in environmentally sensitive areas.

Top-Feed Construction Method
Dry, Bottom Feed Method (Displacement)
This technique uses the same vibrator probes as standard Vibro-Replacement Stone Columns, but with the addition of a hopper and supply tube to feed the stone backfill directly to the tip of the vibrator. Bottom Feed Vibro-Replacement is a completely dry operation where the vibrator remains in the ground during the construction process. The elimination of flushing water in turn eliminates the generation of spoil, extending the range of sites that can be treated. Treatment is possible up to a depth of 80 feet and is not inhibited by the presence of groundwater.

Important Vibro-Replacement Stone Columns Parameters
  • Ground conditions
  • Relative density
  • Degree of saturation
  • Permeation
Vibro-Replacement Stone Columns Design Steps
  1. Perform site investigation
    Soil type, gradation, consolidation, and strength important
  2. Calculate predicted improvement
    Problem understood
  3. Establish requirements of ground improvement
    What settlements, factor of safety, etc., are allowable
  4. Design Vibro-Replacement scheme
    Number of stone columns and/or performance requirements required to achieve desired results
  5. Establish testing criteria
    Load test, SPT, area of stone columns
Method to Estimate Settlement Reduction Using Stone Columns in Cohesive Soils
Expected Vibro-Replacement Stone Columns Results
Vibro-Replacement Stone Columns Quality Control
  • Stone column location
  • Resistance level as measured by amp meter (Vibrator draws more current in denser sols)
  • Quality and quantity of stone added -- friction angle and size of stone columnns
Vibro-Replacement Stone Columns Acceptance Testing
  • Standard Penetration Testing (SPT)
  • Cone Penetrometer Testing (CPT)
  • Dilatometer Testing (DMT)
  • Load Testing
  • Shear Wave Velocity Profiling
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