Vibro Stone Columns

Vibrodisplacement

Ground Improvement by Vibrodispacement (stone columns) is an extremely economical means of enhancing ground bearing capacity and limiting settlements and can elevate the site soil conditions to a level that will perform satisfactorily for the engineering requirements of the proposed structure and has been used effectively in the UK for more than 30 years.

Depending on the ground conditions and performance requirements the technique may be appropriate to support foundations for residential, low rise and industrial buildings, it can also be utilised for treatment to floor slabs, tanks and embankments.

Design

The spacing and depths of the compacted columns is determined by the degree of improvement required to achieve one or more of the following - Limitation of settlement, reduction of differential settlement, increased bearing capacity or increased shear strength.

In ground of variable density or of variable consistency, installation of stone columns may be an effective means of ensuring that the ground performance is made more uniform, thereby limiting differential settlement.

On residential and low rise buildings and industrial developments typical allowable bearing capacities achievable can be in the range of 100kN/m2 to 175kN/m2 for foundation loads.

Method

The top feed method of vibrodisplacement utilises a heavy duty vibrator to drive a cylinder-shaped probe into the ground to penetrate the soils which require improvement, on reaching the required depth the probe is fully extracted and a small charge of aggregate is introduced into the resulting bore from the surface. The probe re-penetrates the bore to within a short distance of the original depth thereby compacting the introduced aggregate. The probe is again extracted and further aggregate added. This is compacted as before during re-penetration to within a short distance of the previously penetrated depth and the procedure is repeated until each stone column is completed to the surface.

In cohesive soils the dry top feed method is suitable where the bore formed during penetration remains open on extraction of the probe to enable introduction of the aggregate, Where this is not the case as in softer cohesive soils or saturated soil conditions the alternative method of dry bottom feed vibrodisplacement may be appropriate. The main feature of this method is that the probe remains in the ground during the whole construction process this provides the necessary support to the open bore. The aggregate is introduced by loading shovel into a storage hopper which is attached to the top of the probe which subsequently allows the aggregate to be fed through the centre of the probe to the tip.

The vibrodisplacement technique displaces the soil sideways therefore there is no spoil brought to the surface, this is especially useful if treating contaminated soils.

Conclusion

Ground Improvement by Vibrodisplacement (Stone columns) is an accepted and very economical solution to improving the load bearing and settlement properties of geotechnical difficult and problematic soils.

The technique allows buildings to be supported on relatively simple and lightly reinforced foundations at shallow depths below ground level with values of differential and total settlements being within acceptable limits.

Programme periods onsite can be dramatically reduced with follow on trades becoming active much more quickly.

There is no spoil generated which means contaminated soils are not brought to the surface therefore eliminating the need for expensive site control and disposal.

On completion of the treatment foundations may be constructed at normal depths while floor slabs or areas of hardstanding may generally be constructed after proof rolling of the surface.

The technique can be used in a wide range of natural soils or in made ground provided that there is not excessive organic content, high silt content or degradable materials.

Find out more about our Vibro Stone Column Projects

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