Deep vibratory techniques using Vibroflots are generally known as vibro compaction and vibro replacement. The techniques are used for densifying granular soils, as well as for realizing stone columns.
A vibroflot is a slim, hydraulically driven vibratory needle. In combination with various accessories, the Vibroflot can be built to use with high pressure water jetting, or for replacement with a hopper system. A Vibroflot can be extended with so-called followers to be able to work to the desired depth. Of course a Vibroflot is used in soft or granular soil, usually sand. The Vibroflots are normally suspended from a standard crawler crane. Real-time data from a single or tandem setup is displayed on the monitor and can be downloaded at any time to support service intervals and job reports.
An known application is the accelerated preparation of reclaimed land by compacting into predetermined patterns. As a result, the ground can be developed immediately. Examples include the Maasvlakte (Rotterdam, Holland) and the expansion of the airport in Singapore.
Another application is to increase load bearing and stability by replacement, for example stone collumns under motorways.
Stone collumns are also made in earthquake-sensitive areas in a pattern around a foundation profile to absorb earthquakes and possibly rising groundwater.
Vibro compaction with a Vibroflot is a deep compaction technique for densifying granular soils with less than 10 – 15% silt present. The process is done 'in situ', using a Vibroflot. Water under high pressure is jetted sideways and downwards from the Vibroflot to assist the penetration process. Under the influence of simultaneous vibration and saturation, loose sand and/or gravel particles are repacked into a denser state and lateral confining pressure within the soil mass is increased. As an option, additional extension tubes can be added to allow the Vibroflot to do its work to depths in excess of our standard 11,5 meter (38 feet) below surface level up to depths of more than 25meter (82 feet). The minimum working depth is about 8 meter (26 feet)
Vibro replacement is a technique used in soils that do not respond well to vibration alone (too adhesive, more than 15% silt). The improvement is achieved by creating columns of either crushed stone or concrete (reinforced). The process enables increased load bearing, reduces settlement and even improves the shear resistance of the ground being treated. The process is technically proven and cost effective.
Vibro replacement involves two primary construction methods: Wet Top Feed and Dry Bottom Feed.
Wet Top Feed Method
In the Wet Top Feed Method water and/or air under high pressure is jetted from the nose of the Vibroflot to assist with the penetration. It removes soft material and helps to stabilize the space created by the Vibroflot, to ensure that the backfill material reaches the nose cone of the Vibroflot.
Dry Bottom Feed Method
In this method a hopper system and a supply tube support the Vibroflot. This hopper system and supply tube feed the stone backfill directly to the nose cone of the Vibroflot. As bottom feed, vibro replacement is a completely dry operation. The Vibroflot remains in the ground during the construction process.