Glossary for Vibratory Ground Improvement

A high vertical force of typically several tons, is produced by a Vibroflot when building a Stone Column. This force results from either the dead weight of the vibroflot or a combination of weight and crowd force if such a vibroflot is held by an excavator or drill rig with push-down (crowd) force capability.

German abbreviation for VCC  (Betonrüttelsäule)

Cone Penetration Test, also called “Dutch Cone”. A rod with a conical tip is pushed in the ground at a constant speed while its tip and sleeve resistances are recorded. The CPT test gives an indication of soil density and soil type.

The radial stress between soil and Stone Column. The higher such stress, the more vertical load a column can carry. A high eccentrical force of a vibroflot is beneficial to create strong confinement.

The portion of the time-settlement of a soil, which is governed by the dissipation of excess pore pressures.

A void ratio for which a soil sample is in a state of density at a given stress level, for which it does neither contract nor dilate upon shearing. This state is also called the “critical state”.

Stone Column volume in percent of the volume of the unit cell. Usually lies in the range of 5 % to 30 %.

A stone column installed in a way that the gravel is transported without the aid of water in a special duct (tremie pipe) alongside the Vibroflot.

In this method, water can be added during the penetration phase to reduce the wall friction of the vibroflot entering the soil.

The method by which the gravel is dumped into an open hole, either predrilled or created with the vibroflot. This method works only if the hole does not collapse, i.e. in stable soil, generally above groundwater.

A Vibroflot vibrates due to one or more eccentrical masses rotating inside its lower section. A higher eccentrical mass and a higher vibration frequency increase both the eccentrical force.

German abbreviation for Dry Mix Concrete Column (FertigmörtelStopfsäule)

Normally Consolidated: A soil which was never in the past under a higher overburden pressure than today. OC, over consolidated

Over Consolidated: A soil which was in the past under higher overburden stress than today. Consequently, such soil behaves relatively stiffer under a loading until it reaches the value of the maximum past overburden stress.

Over Consolidation Ratio: Factor of how much higher the maximum ever overburden stress on the soil is compared to today’s stress level.

The phase of lowering the Vibroflot to the required depth.

Device to measure water pressure in soils. Tensiometer

Pressuremeter test

Rules to operate a Vibroflot when installing a Vibro Compaction. Usually, a threshold amperage and time, whichever comes first, for which the Vibroflot pulled 0.5 m again to 1.0 m upwards.

German abbreviation for Vibro Compaction (Rütteldruckverdichtung)

A value given in percent indicates the void ratio achieved due to compaction relative to what could be achieved for the same material in standardized tests determining the loosest deposit (Relative Density 0 %) and the densest deposit (Relative Density 100%). Attention: 100% is not the maximum obtainable value like it is for example for soil sample water saturation. A Relative Density of 100%, if achieved in field testing, only means that compaction to has been achieved with the same void ratio as the standardized maximum density laboratory compaction test for this site. Very high Vibro Compaction efforts are not uncommon to result in over 100 % Relative Density.

German abbreviation for Vibro Replacement and/or Stone Column (Rüttelstopfverdichtung)

During the installation of Stone Columns, when the Vibroflot is lowered back into the gravel to enlarge the column diameter to the desired value.

The volume of washed-out soil which was later replaced by gravel, given in percent of the total volume of a unit cell
see also displacement factor

The phenomenon is that granular in-situ soil flows towards the Vibroflot in a way that makes feeding from the top obsolete.

Standard Penetration Test. A very widely used sounding device, measuring the number of blows necessary to drive a split barrel sampler 1 ft (≈ 30 cm) into the soil. Mostly done from the bottom of a borehole.

An indicator of soil behaves as dilating or contracting upon shearing. It is a parameter derived from Critical State Soil Mechanics and a measure of how much a void ratio at a particular stress level is smaller or larger than the critical void ratio. If the state parameter is a negative number, it means the soil sample with this state parameter will behave dilatant upon shearing, which means it would not build up excess pore pressures and hence not liquefy. For a positive number the soil would behave contracting upon shearing and hence, if submerged, have the potential to build up excess pore pressures and eventually liquefy.

Column of granular material, mostly gravel, installed for drainage and/or load bearing, mostly used in cohesive non-compactable soil.

Piezometer that is sealed against the atmosphere and thereby can also measure suction (capillary) water pressures below 1 bar.

Feeding granular material with a loader to the compaction point from the top of the hole, compare self-feeding.

Zone of soil around a stone column that can be attributed as belonging to that column. (In an infinite stone column mesh with equal soil conditions and equal loading conditions, at the border between two unit cells, the horizontal deformations in the soil are zero.)

Vibro Concrete Column. A column installed using a Vibroflot and pumpable concrete BRS.

The horizontal vibration of the tip of the Vibroflot measured in mm when free-hanging in the air. Manufacturers quoting such values for their equipment traditionally use the double amplitude (German: Schwingweite).

Procedure to compact granular soil by vibration using a Vibroflot
see also Vibroflotation

Torpedo-shaped vibratory probe with rotating eccentric weights on its lower end for Vibro Compaction and Stone Column installation. Vibroflots, as opposed to vertically vibrated beams or rods, generate strong horizontally polarized shear waves that have a large lateral reach for compacting the soil.

Procedure name as well as a company name. As a procedure name, it is equivalent to Vibro Compaction. The term describes that all granular soils first have to float before moving into a denser state. The floating state is achieved by vibration.

Name for a procedure of installing “Stone Columns”, expressing that most of the soil is displaced laterally by the stone column and not washed out. This is often the case for the Bottom Feed method and the Dry Top Feed method

Name for a procedure of installing “Stone Columns”. The term replacement is expressing that the soil is more replaced than displaced. This is often the case for the Wet Top Feed method.

The ratio of the pore volume of soil over the volume of solid matter. For clays, Void Ratios larger than 1 are not uncommon, while for most granular soils they lie below 1.

German Abbreviation for Vibro Mortar Columns (Vermörtelte Stopfsäule)

Installation method where the gravel is added from the top of the hole using flushing water to keep open an annular space around the Vibroflot.