SOIL IMPROVEMENT
Vibro Compaction, Vibro Replacement, Dynamic Compaction, Dynamic Replacement, High Energy Compaction, Rapid Impact Compaction
VIBRO COMPACTION
Vibrocompaction, established in 1936 in Germany, is one of the earliest and most effective dynamic deep compaction methods. This technique significantly enhances the compaction of non-cohesive soils, yielding superior results. The process involves densifying soil using deep vibration probes, either single or double, which are suspended from a crane. Soil densification is quantified by the settlement observed at the ground surface, while increases in bearing capacity are evaluated through zone load tests. Further assessment of soil property improvements is conducted using Cone Penetration Tests (CPT) before and after compaction.
During vibrocompaction, points are strategically chosen in either triangular or square patterns to comprehensively improve the targeted area. The process utilizes a cylindrical vibrator that oscillates horizontally, typically suspended from a crane. These vibrators, ranging from 15–40 kN in weight, 30–50 cm in diameter, and 2–5 m in length, reach the desired depth through extension tubes. These tubes also house supply pipes for water and, optionally, air to assist the ground penetration process. The resulting settlement from this compaction can vary from 5% to 15% of the compaction depth, depending on the initial soil density and the desired level of compaction. Detailed technical descriptions and further information on vibrocompaction can be found in specialized literature.
VIBROREPLACEMENT AND STONE COLUMNS
An advancement to the Vibrocompaction is the vibroreplacement method. That is pouring crushed stone or coarse graded sand or gravel into the hole made by the Vibrocompaction probes.
After the vibrator is lifted, the temporarily stable cylindrical cavity obtained is filled with coarse material. The coarse material is then compacted by repetitive use of the vibrator. This vibroreplacement procedure came to be known as the conventional dry method. Such technique allows to get dense stone column construction for a greater range of weak natural soils and man-made fills. Vibroreplacement getting wide attention and has good reputation in stabilizing foundation soils for many types of structures especially housing and low-rise buildings.
The conventional dry method utilizes the vibrator to displace the surrounding soil laterally, then the crushed stone is pressed laterally into the soil during both the cavity-filling stage and compaction stage. This produces stone columns that are tightly interlocked with the surrounding soil. The conventional dry method produces stone columns to depths of 8m in cohesive soils that have very low shear strengths.
This method is different than the conventional stone columns where the soil is drilled with boring machines and the borings filled with stones.
Another way for vibroreplacement is that the replacing soil or stones may be fed from bottom during vibration with vibrators having deep feeding nozzles. In bottom feeding vibrators, the stones or sands are fed during lifting the vibrator so all cavities will be filled and it overcomes collapse as well.
On the other hand, the wet vibroreplacement method is used for cohesive soils where a heavy water jet flushes the soil and allows a room for the replacement.
VOn the other hand, the wet vibroreplacement method is used for cohesive soils where a heavy water jet flushes the soil and allows a room for the replacement.