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The BG 24 H is – like all rigs of the BAUER BG-series – primarily designed as a rotary drilling rig for several drilling methods such as Kelly drilling, CFA-system, FDP displacement piling.
The possibility of using a BG rig for other methods by adding various attachments is an in-built advantage of the BG series. It can be used as carrier for soil-mixing methods SMW and CSM. The attachment of hydraulic hammers (FAMBO) or Diesel hammers (PILECO) is another application. Bigger BG rigs are suitable for mounting BC trench cutters.
The versatility of the BG 24 H was demonstrated on a big soil improvement contract in Croatia. Soft sandy silt subsoil underneath a new highway junction near Split had to be improved with 60.000 linm of stone columns to reduce settlement and increase the bearing capacity. The column length ranged from 9 m to 16 m with a design diameter of 600 mm.
Bauer Maschinen modified a BG 24 H drilling rig of our customer Geotehnika-Inzinjering to a carrier for a bottom-feed depth vibrator TR 17.
In cohesive soils the soil particles cannot be rearranged by vibrational impulses. A considerable increase in bearing capacity can, however, be achieved in these soils by the vibrodisplacement process. With the vibrodisplacement technique stone columns are constructed by a BAUER depth vibrator specially adapted and equipped for this process.
Assisted by air flushing, the vibrator penetrates the soil to the required depth. The surrounding soil is displaced as a result. Coarse granular backfill material is delivered directly from a hopper to the tip of the vibrator through the material transfer pipe attached to the front of the vibrator. During withdrawal of the vibrator, the annulus formed below the tip of the vibrator is immediately backfilled with the gravel or crushed stone supplied through the material transfer pipe. By repeated raising and lowering of the vibrator in steps of around 0.3 to 0.5 m the backfill material is compacted and displaced laterally and forced into the surrounding soil. With this technique it is possible to increase the average stiffness modulus of the soil by a factor of 2 to 3.
Vibrodisplacement stone columns can also facilitate drainage of layered soil formations. Excess pore water pressures can be rapidly dissipated through the open grain structure of the stone columns. This feature offers considerable advantages particularly in earthquake zones by preventing liquefaction of the soil during earthquakes. In addition, horizontal vibrations can be dampened by the relative flexibility of the foundation.