14 Ground improvement by deep vibratory methods
Scheidig reported in 1940 on an interesting work for the foundation of a
large grain silo at Bremen, where, for the first time, the method was used to
increase the bearing capacity of bored piles by compacting the sand below
the toe and along the shaft of the piles.
During the war, construction activities were increasingly directed toward
military installations or for facilities closely connected with the wartime
economy. Were these to be built on alluvial deposits, or in the vicinity of the
shoreline, the natural density of the sands was frequently insufficient to carry
substantial structural loads using normal shallow foundations without intolerably high deformations. Increasingly in these cases, the vibro flotation method
was used by which sand could be compacted sufficiently to carry even the
highest loads. In this way, it was possible to avoid expensive pile foundations
for which concrete and steel were needed, an effect that was most welcome
given the shortage of almost all raw materials. Also, there were major military
shelters at Rotterdam and near Bremen where the in-situ or dredged sand was
compacted by vibro flotation to such a degree that these heavy structures could
be built using incredibly high bearing pressures. At Rotterdam, where a submarine bunker was built, Casagrande proposed an allowable bearing capacity
of 15 kg/cm 2 (1.5 MPa) to be used, for which a spacing of the compaction
centers of 4 m 2 was necessary. To accelerate the work, the compaction grid was
widened to 5 m 2 per probe and the bearing pressure was reduced to 10 kg/cm 2
(1.0 MPa). Figure 2.8 shows a cross section through the submarine shelter.
Figure 2.7 Vibro compaction employing wooden gantry, 1939. (Courtesy of Degebo,
Berlin, Germany.)
Scheidig reported in 1940 on an interesting work for the foundation of a
large grain silo at Bremen, where, for the first time, the method was used to
increase the bearing capacity of bored piles by compacting the sand below
the toe and along the shaft of the piles.
During the war, construction activities were increasingly directed toward
military installations or for facilities closely connected with the wartime
economy. Were these to be built on alluvial deposits, or in the vicinity of the
shoreline, the natural density of the sands was frequently insufficient to carry
substantial structural loads using normal shallow foundations without intolerably high deformations. Increasingly in these cases, the vibro flotation method
was used by which sand could be compacted sufficiently to carry even the
highest loads. In this way, it was possible to avoid expensive pile foundations
for which concrete and steel were needed, an effect that was most welcome
given the shortage of almost all raw materials. Also, there were major military
shelters at Rotterdam and near Bremen where the in-situ or dredged sand was
compacted by vibro flotation to such a degree that these heavy structures could
be built using incredibly high bearing pressures. At Rotterdam, where a submarine bunker was built, Casagrande proposed an allowable bearing capacity
of 15 kg/cm 2 (1.5 MPa) to be used, for which a spacing of the compaction
centers of 4 m 2 was necessary. To accelerate the work, the compaction grid was
widened to 5 m 2 per probe and the bearing pressure was reduced to 10 kg/cm 2
(1.0 MPa). Figure 2.8 shows a cross section through the submarine shelter.
Figure 2.7 Vibro compaction employing wooden gantry, 1939. (Courtesy of Degebo,
Berlin, Germany.)