Soil improvement in specialist foundation engineering

Soil improvement methods aim to increase the load-bearing capacity of the subsoil and prevent settlement of the future structures. Furthermore, they can reduce soil liquefaction (for instance in the event of earthquakes). Deep vibration methods are often a fast and economical option for improving the technical characteristics of the construction soil. Apart from vibro compaction and vibro replacement, vibro concrete columns are also used for this purpose.  

Vibro flotation densification (RDV)

This method is used for self-compaction of soils with insufficient bulk density, for example non-cohesive, naturally undisturbed soil or artificially poured sands and gravels. Through the vibrations of the vibrator, the soil particles are brought into a more compact distribution. After the end depth is reached with the help of flushing, gradually removing the silo vibrator creates a densified zone with a diameter of 2 to 4 m. The reduced pore volume can be seen on the surface through the formation of a settlement funnel that must be filled in.

Vibro replacement

This method is used on soils with more than 10% cohesive particles. With the “Bottom Feed” VR, however, the leader-guided bottom feed vibrator is brought to the end depth using flushing air and active crowd force. The installation material is transported directly to the outlet on the vibrator tip using a feed unit and charging pipe, then radially displaced and compacted in tamping stages. The tamping pattern (quantity, pressure) is defined and monitored individually. 

Soils with more than 10 % cohesive particles can no longer be moved and compacted using vibrations. The soil improvement that can be achieved here comes from the construction of load-bearing gravel columns. For VR “Top Feed”, the vibrator is brought to the end depth with the help of water or water/air. The installation material added at the surface reaches the vibrator tip through the annular gap that is created. Through continual tamping movements, the material is radially displaced and compacted until a pre-defined stopping factor (hydraulic pressure, gravel volume) is reached.

The Vipac method can be used to construct sand and gravel columns in a relatively easy and cost-effective manner. The method is based on alternating between lowering and pulling up the pipe. The material can be filled with a telescoping loader even during vibration.

Vibro Concrete Columns (VCC)

Vibro concrete columns are used when fine grained soils are unable to form a load-bearing bond with displacement columns or if the lateral support forces are too low. The surrounding soil is not compacted. Rigid support elements are used to bridge non-load-bearing soil strata. After reaching a load-bearing foundation level, the vibrator is withdrawn and the cavity created is filled with concrete under constant concrete pressure. VCC piles are calculated like unreinforced piles.

Dynamic soil compaction (BDC)

Dynamic soil compaction (Bauer Dynamic Compaction BDC) is particularly suited for increasing the bulk density of non-cohesive, friable soils and loose mixed soils with a low fine aggregate content. For this method, a heavy drop weight is repeatedly dropped onto the ground from a great height. The kinetic energy emitted on impact penetrates into deeper soil strata and leads to compaction via forced re-packing of the grains. The degree of compaction depends on the mass of the drop weight, the fall weight and the spacing between points. The method is generally used on backfill, demolition material, construction debris and soil strata with large cavities (karst).

Flying Vibro 75

A high flyer that stays down to earth: With the Flying Vibro 75, BAUER Maschinen GmbH is defining the future of soil improvement.

BAUER BF 15: A complete system for the construction of stone columns using depths vibrators.

The BAUER BF 15 is a complete system for the construction of stone columns using dephts vibrators.

Soil improvement with vibro replacement (VR) Bottom Feed


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Franz-Werner Gerressen
Head of Process Development

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