This technique involves the improvement of weak soils by the installation of densely compacted columns made from gravel or similar material with a vibrator. The displacement process reinforces all soils in the treatment zone and densifies surrounding granular soils. It’s a technique first developed by our company founder, Johann Keller, that we’ve used on thousands of projects.

Keller rigs demonstrating the vibro stone column technique

Common uses

Reduce foundation settlement
Increase bearing capacity, allowing reduction in footing size
Increase stiffness
Increase shear strength
Reduce permeability
Mitigate potential for liquefaction
Permits shallow footing construction in treated fills
Very effective for sand compaction and land reclamation

Process

In the top-feed process, the vibrator penetrates to the design depth using the vibrator’s weight and vibrations, as well as air jets located in the tip. The stone (crushed stone or recycled concrete) is then added at ground level to the space created around the vibrator. The stone falls through the space to the vibrator tip, and fills the void created as the vibrator is lifted a few hundred millimetres. The vibrator is then lowered, densifying and displacing the underlying stone. This vibro replacement process is repeated in lifts until a dense stone column is constructed to the ground surface.

The bottom-feed process is similar, except that the stone is fed to the vibrator tip through an attached feed pipe. Pre-drilling of dense strata may be required for the vibrator to penetrate to the design depth.

Vibro rigs can be fully instrumented with an on-board data acquisition system. Data from the system, such as amperage and lift rate, can then be recorded and displayed in real-time alongside specified target values on an in-cab monitor. This monitoring allows the operator to correct any deviations in real-time during the construction process to keep the vibro compaction within project specifications.

Variations on the product include vibro concrete columns where concrete is pumped into the ground through the vibrator, and environmental stone columns where a plug of cement-based grout or weak concrete is placed at the base of the column.

Advantages

Offers an economical alternative to piling
A versatile ground-improvement method than can be adjusted to a wide variety of soil conditions and foundation requirements
Can be carried out to depths of up to 15 metres
Relatively quick execution so subsequent structural works can follow very quickly
Enables standard shallow foundations which can lead to savings
Environmentally-friendly as recycled materials can be used
Extremely quiet with low vibration

Quality assurance

The vibro equipment we use is designed and manufactured by our in-house equipment manufacturer exclusively for use by Keller companies.

In-house quality production management software enables us to capture and analyse data in real time and valid the performance of the ground improvement being carried out.

A variety of production parameters are generally logged during execution including depth, current, pull down force, uplift/pull down sequence, time and date and element number.

Field trials can also be used to verify column production parameters, along with static load tests, single or group, column material compressive strength tests, and column diameter verification.