A history of vibratory deep compaction 7
as a result of intensive vibrations. Realization of the method required rather
complicated watering systems and, above all, powerful surface vibrators
to compact the sand in sufficiently thick layers. Even the strongest surface
vibrators at the time did not reach deeper than 2.50 m, which limited the
new method considerably.
The compaction of sand at large depths was required for the construction of the new Congress Hall at Nuremberg. The designers of this gigantic
project had high demands for the durability of its foundations in the light of
the aggressive groundwater, and this could not be fulfilled by conventional
methods. Also, the dimensions of the structure were exceptional, and so
were its loads: the main hall measured 260 × 265 m; the ceiling was 65 m
high with a free span of 160 m from wall to wall. The subsoil consisted of
sand deposits that extended to 16 m depth where strong sandstone started.
As no proven methods existed for compacting this sand, the designer
proposed a field trial to be carried out under the supervision of Degebo
(German Research Society for Soil Mechanics). Two compaction methods
were to be tested and compared: (1) a modified Franki method and (2) the
newly developed so-called Keller method. Trial compaction finally commenced in 1936.
The Keller proposal was as follows:
1. To build vibrators following the principle of a bob weight connected
to an electric motor in cylindrical form on a vertical axis with a strong
horizontal force
2. To bring the vibrator by means of a bore hole into any desired depth of
the sand to be compacted. Figure 2.2 shows the fundamental arrangement of the new method: the vibrator has been lowered inside the borehole to the deepest layer of the sand to be compacted, and the casing
has been pulled out to the extent that the vibrator is fully surrounded
by the sand. Vibrator and casing are simultaneously extracted in this
position with progressing densification. Compaction is accordingly
achieved in layers progressing from below to the surface
Loos (1936) reported for the first time before an international audience
about this novel method of soil compaction during the first International
Conference on Soil Mechanics and Foundation Engineering held in 1936 at
Cambridge, Massachusetts in Section M that was particularly devoted to
“Methods for improving the physical properties of soils for engineering
purposes.”
What had been so simply and convincingly formulated at the time, represented in reality a major technical problem: by means of a heavy wooden
23 m high gantry, a 460 mm diameter drilling casing was lowered through
16 m of sand down to the Keuper sandstone employing conventional boring
methods. Then the 2 m long vibrator was introduced. It should be emphasized that this was to generate horizontal vibrations in contrast to the
as a result of intensive vibrations. Realization of the method required rather
complicated watering systems and, above all, powerful surface vibrators
to compact the sand in sufficiently thick layers. Even the strongest surface
vibrators at the time did not reach deeper than 2.50 m, which limited the
new method considerably.
The compaction of sand at large depths was required for the construction of the new Congress Hall at Nuremberg. The designers of this gigantic
project had high demands for the durability of its foundations in the light of
the aggressive groundwater, and this could not be fulfilled by conventional
methods. Also, the dimensions of the structure were exceptional, and so
were its loads: the main hall measured 260 × 265 m; the ceiling was 65 m
high with a free span of 160 m from wall to wall. The subsoil consisted of
sand deposits that extended to 16 m depth where strong sandstone started.
As no proven methods existed for compacting this sand, the designer
proposed a field trial to be carried out under the supervision of Degebo
(German Research Society for Soil Mechanics). Two compaction methods
were to be tested and compared: (1) a modified Franki method and (2) the
newly developed so-called Keller method. Trial compaction finally commenced in 1936.
The Keller proposal was as follows:
1. To build vibrators following the principle of a bob weight connected
to an electric motor in cylindrical form on a vertical axis with a strong
horizontal force
2. To bring the vibrator by means of a bore hole into any desired depth of
the sand to be compacted. Figure 2.2 shows the fundamental arrangement of the new method: the vibrator has been lowered inside the borehole to the deepest layer of the sand to be compacted, and the casing
has been pulled out to the extent that the vibrator is fully surrounded
by the sand. Vibrator and casing are simultaneously extracted in this
position with progressing densification. Compaction is accordingly
achieved in layers progressing from below to the surface
Loos (1936) reported for the first time before an international audience
about this novel method of soil compaction during the first International
Conference on Soil Mechanics and Foundation Engineering held in 1936 at
Cambridge, Massachusetts in Section M that was particularly devoted to
“Methods for improving the physical properties of soils for engineering
purposes.”
What had been so simply and convincingly formulated at the time, represented in reality a major technical problem: by means of a heavy wooden
23 m high gantry, a 460 mm diameter drilling casing was lowered through
16 m of sand down to the Keuper sandstone employing conventional boring
methods. Then the 2 m long vibrator was introduced. It should be emphasized that this was to generate horizontal vibrations in contrast to the