The International Information Center for Geotechnical Engineers

Vibroflotation

Introduction

Loose soils are a well documented problem, common in the construction industry. Immediate settlements of 1 inch per foot (depth) of loose sand can occur in worst-case scenarios. Contractors have two main options: use deep foundations to bypass the unfavorable layers, or use a compaction technique to improve the site conditions (D’Appolonia, 1954). Vibroflotation was first used in Germany in the 1930s and first appeared in the United States in 1948 when the Bureau of Reclamation studied the possibilities for sand and silt compaction at the site of the Enders Dam in Nebraska (D’Appolonia, 1954).

The term vibroflotation is often used interchangeably with vibrocompaction in the literature. However vibrocompaction is a broader term that encompasses two different techniques. The first is vibroflotation, which uses a vibroflot that vibrates horizontally. The second utilizes a vibrating probe which vibrates vertically. It should be noted that vibroflotation is used as a mechanism for implementing vibro-replacement, a method which combines the technique of vibroflotation with gravel backfilling in order to create stone columns. This is a review of vibroflotation only.

Vibroflotation utilizes horizontal vibrations in conjunction with fluid  to reduce the interparticle friction of the surrounding soil. This allows the material to densify and creates a column with improved engineering characteristics, including an increase in strength and a reduction in compressibility. Figure 2 displays the transition of soil from a loose state to a dense state. The goal of vibroflotation is to increase the relative density of a soil.  This increase in relative density results in reduced settlements as well as improved resistance to liquefaction.

Figure 2: Soil Densification (Bauer Maschinen GmbH, 2012)

Figure 2: Densification of soil during vibroflotation (Bauer Maschinen GmbH, 2012)

Several factors, including the equipment size and quality, spacing and pattern, in situ material, vibroflot withdrawal technique, backfill material, and workmanship greatly affect the level of density achieved during vibroflotation (Brown, 1977).

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