VR, Vibro Replacement - Dry Bottom Feed
The reasons behind it...and the methods

Vibro replacement stone or concrete columns are ground improvement techniques to improve the load bearing capacity and reduce the settlement of the soil. On many occasions, it is noted that the local soil is by nature, unable to bear the proposed structure. Hence the use of ground improvement techniques may be necessitated. Use of stone columns is one such technique. The stone column consists of crushed coarse aggregates of various sizes. The ratio in which the stones of different sizes will be mixed is decided by design criteria. The aforementioned crushed aggregates in the definite proportion are to be placed into the soil at regular intervals throughout the area of the land where the soil bearing capacity is to be improved. This is done either by using either the dry bottom feed or the wet top feed vibratory systems which are driven into the ground. The aggregates are then allowed to take the place of the displaced soil which exerts a pressure on the surrounding soil, hence helping to improve the soil's load-bearing capacity. The vibrating pore breaks down the pores of the surrounding soil, thereby densifying the soil. The crushed aggregates or the gravel that is poured in takes the place of the soil keeps up the pressure on the soil that was created by the vibrating probe. These columns are made across the area to be built on in a grid pattern at regular intervals.

Typical Vibro Replacement Results
Ground Type Relative Effecetiveness
Densification Reinforcement
Sands Excellent Very good
Silty sands Very good Very good
Non Plastic Silts Good Excellent
Clays Marginal Excellent
Mine spoils Depending on graduation Good
Dumped fill Good Good
Penetration

When suspended from a standard crawler crane the Vibroflot penetrates to the required depth under its own weight. When mounted on a leader of a suitable base machine the Vibroflot penetrates to the designed depth with the assistance of a pull down winch, thus increasing the efficiency and speeding up the penetration time. When as an attachment to an excavator the Vibroflot penetrates to the required depth with the assistance of the boom.

Replacement

Crushed stone is introduced (with the aid of a skip) into the hopper and is fed down the supply tube to the specially adapted nose cone. The Vibroflot is then lifted a set value and the stone is discharged to the underside of the nose cone. The Vibroflot re penetrates and the horizontal forces of the Vibroflot laterally compacts the stone against the surrounding soil.

Completion

This process is repeated up to the designed cut-off level, forming a well compacted tightly- interlocked stone column surrounded by compacted soil of enhanced density.