This technique involves construction of concrete columns with a bottom-feed, down-hole vibratory probe to transfer loads through weak strata to a firm underlying stratum.

Vibro concrete columns technique illustration

Common uses

Reduce foundation settlement
Increase bearing capacity, allowing reduction in footing size
Increase stiffness
Increase shear strength
Reduce permeability
Mitigate potential for liquefaction
Provide slope stabilization

Process

A bottom-feed, down-hole vibratory probe is advanced through the weak strata to the underlying firm stratum. Granular bearing soils are densified by the vibrator. Concrete is then pumped through the bottom-feed tremie tube. The vibrator is raised and lowered several times within the bearing depth to construct an expanded base. The vibrator is then raised to the surface as concrete fills the void created by the vibrator during extraction. Typically, the vibrator also re-penetrates the top of the column to construct an enlarged head, which can be overlain by a geogrid reinforced soil relieving platform.

Advantages

A versatile ground improvement method that can be adjusted to a wide variety of soil conditions and foundation requirements
Offers an economical solution for ground improvement
Can be carried out to almost any depth
Relatively quick execution so subsequent structural works can follow very quickly
Soil improvement enables standard shallow footings which can lead to savings
Extremely quiet with low vibration
Only a small quanitity of soil has to be removed during the process so avoids the cost of spoil removal associated with continuous flight auger and bored piling systems

Quality assurance

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.