The International Information Center for Geotechnical Engineers

Vibroflotation

Applicable Soils

The suitability of site conditions is the most important factor when considering vibratory compaction as a solution. Most coarse-grained soils with fines content of less than 10% are considered acceptable for this method, i.e. sands, gravels, and slags. A grain size distribution showing the range of applicable soils is presented in Figure 3. Vibroflotation has been found to work best for loose granular materials located below the water table.

Figure 3: Grain size distribution for applicable soils (Bauer Maschinen GmbH, 2012)

Figure 3: The orange area represents the grain size distribution of soils suitable for vibroflotation (Bauer Maschinen GmbH, 2012)

Clay layers, excessive fines content and organics can all cause serious complications when attempting to improve a site with vibroflotation. These materials generate excess pore water pressures which greatly inhibits volume change and results in preventing the granules to move into a denser state. To accomodate some of these issues, "earthquake drains" is a possible solution for sites which are susceptible to liquefaction (Rollins et al, 2003).  The vibrations are also significantly damped in the presence of these soils, and reduces the radial densification dramatically. If the in situ material particle size is too great, the penetration of the vibroflot is greatly hindered which increases the amount of time needed to achieve adequate compaction. This can make the technique very expensive (Brown, 1977).

In order to accurately depict the site characteristics through grain size distribution, sieve tests are needed in order to assess a large number of samples. A good alternative to this method is the use of the cone penetration tests (CPT). The results from a CPT offer a continuous soil profile at each location and measures variations through correlations in soil strength, compressibility and hydraulic conductivity if the piezocone is used (Massarsch, 2005).

Figure 4: CPT applicability (Massarsch, 2005)

Figure 4: CPT applicability (Massarsch, 2005)

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