Mostly loose and mixed soils usually have insufficient lift characteristics and are not able to self-thicken by vibration alone. In these cases the technology of vibrocompact gravel columns can be applied. The system is also suitable for the improvement of both fine and coarse landfill.
The pneumatically charged vibro is mainly used, where the gravel filler material comes out directly under the air pressure at the tip of the tool (BOTTOM FEED method). Dry infixing is obtained thanks to a special drill mounted on a drill.
The action of the tirabasso involves an optimal compaction of the gravel column (activation) and an extension in depth of the thickening beyond the maximum depth reached. The column is formed by successive steps of extraction, spillage and crushing of the gravel both downwards and sideways. In this way columnar elements are obtained which, interacting with the ground (TOP FEED method) contribute to the improvement of the bearing capacity of the consolidated stratifications, (they support the loads and allow the limitation of expected settlements within the project limits).
The dry method, without drilling fluids, associated with the use of only natural gravel allows operation in conditions of maximum environmental compatibility.
The technology is also widely used on issues of mitigation of liquefaction risk thanks to three effects, the stiffening of the ground due to the presence of gravel columns, the compaction of the interlocked soil between the columns, the drainage that guarantees the dissipation of interstitial overpressures.