Vibro Compaction

Typical requirement for Post Compaction CPT sounding

The Aging Effect

An increase of CPT result is clearly visible after a waiting period of eleven days in comparison to only five days (sand compaction on Hong Kong Airport project).

Design and Quality

Quality Assurance

Foundation engineering is the civil engineering discipline with the highest potential for variance between assumed behaviour and actual as-built behaviour. This stems from the large uncertainties in the characteristics of the building material, the in-situ soil. No matter how much field and laboratory exploration data is available, the unknowns and uncertainties will always be greater than for steel, concrete and other construction materials.

Detailed measurements and observations are therefore of paramount importance and an efficient quality assurance/control system is mandatory. Modern data acquisition systems intelligently combined with equipment built to allow for the exact measurement of process parameters (such as a precise gravel consumption by volume over depth) are now available.

Quality Control for Dry Bottom Feed Stone Columns

Digital quality control for dry bottom feed stone columns

In order to be able to print out column diameter variations with depth, it is necessary to measure precisely the volume of each gravel batch and the depth, at which it was placed in the ground.The Double Lock Gravel Pump is the optimal machine for an exact gravel volume control. This volume measurement is particularly useful for offshore (marine) stone column installation, where a visual control of the gravel consumption or gravel loss on the seabed is not possible.

Quality Assurance for Vibro Compaction

Quality control for a Vibro Compaction consists of the following steps :

  • Before compaction
    Determine Pre-Compaction CPT or SPT sounding.Establish the Pre-Compaction ground level of the compaction area.
  • During compaction
    Record ampere variation with depth during every compaction point installation.

Analog data logger
showing ampere over time (blue) and depth over time (red).
CPT results before and after compaction. The non compacted layers result from a silt content exceeding 10 %.Digital data logger showing depth variation with time on the left and amperage variation with time on the right. (two vibroflots - "tandem" operation)
  • After compaction
    Determine Post-Compaction CPT or SPT sounding and adjust for Post Compaction ground levels.

Post-compaction cone penetration tests (CPT) compared to the pre-compaction test and showing the improvement achieved versus the specified minimum performance line.