A history of vibratory deep compaction 23
vibro flotation works were already being carried out by the late 1950s in
these countries using vibrators from Germany and the United States. From
about 1965, the Cementation Company in the United Kingdom built its
own vibrators with similar features to the American equipment. However,
in 1968, the electric motor was replaced by a hydraulic drive.
More important than these mechanical modifications was the fact that
depth vibrators were now increasingly also used in the United Kingdom for
the improvement of fine-grained cohesive soils. The application of stone columns in soft soils was accompanied by efforts to develop suitable criteria for
the design of this ground improvement method (e.g., Thorburn et al., 1968).
Vibro flotation foundations and, since 1968, also vibro replacement stone
column foundations were carried out on some very large international projects, and this made the method known on all continents.
From 1955 to 1958, extensive compaction trials were carried out by the
Keller Company to establish the design criteria for the foundation of the
Aswan High Dam (Sad al-Ali) now retaining Lake Nasser in Upper Egypt.
The effect of vibro flotation performed under water in hydraulically placed
fine to medium dune sand was investigated and compared with the results of
compaction by blasting. It was found that densification of the sand by vibro
compaction was superior to that by blasting (Figure 2.14), and the Board of
Consultants for the Sad al-Ali Commission, led by Terzaghi, recommended
compacting approximately 3.4 million m 3 of dredged sand through 35 m of
water under the core of the dam by this method. The Suez crisis of 1956 and
the political tensions thereafter rendered the financing of the project difficult
and prevented the contract award to an originally favored German construction consortium. The gigantic project was finally financed and built by the
Soviet Union, and purpose-built Russian vibrators were used to compact the
sand from 1965 to 1967. Apart from the information that these machines
were operated at 1750 rpm, no other characteristics became known, nor did
the equipment appear again on the international market.
Of similar scale was the foundation work carried out in 1960–1963 for
the Usinor steel works at Dunkirk in France. The subsoil consisted of alluvial
fine sands to a depth of up to 30 m, frequently interspersed by silt and clay
layers, occasionally even peat. Stiff clay followed below requiring relatively
deep embedment of an alternative piled foundation. The economical and
practical advantages of a vibro compaction solution convinced the client to
follow the recommendations of its foundation consultant, Kerisel, for shallow foundations on vibro-compacted sand, in preference to the piled option.
The vibro approach additionally enabled detailed planning to be carried out
after the whole area was first compacted, providing program advantages for
projects of this size. In less than two years, some 480,000 lin.m of compaction were carried out. Where necessary, the cohesive layers were bridged by
large diameter vibro replacement stone columns built by two vibrators (in
places even four) suspended 80 cm apart from each other from one crane
using particularly strong water flush. The works were performed in double
vibro flotation works were already being carried out by the late 1950s in
these countries using vibrators from Germany and the United States. From
about 1965, the Cementation Company in the United Kingdom built its
own vibrators with similar features to the American equipment. However,
in 1968, the electric motor was replaced by a hydraulic drive.
More important than these mechanical modifications was the fact that
depth vibrators were now increasingly also used in the United Kingdom for
the improvement of fine-grained cohesive soils. The application of stone columns in soft soils was accompanied by efforts to develop suitable criteria for
the design of this ground improvement method (e.g., Thorburn et al., 1968).
Vibro flotation foundations and, since 1968, also vibro replacement stone
column foundations were carried out on some very large international projects, and this made the method known on all continents.
From 1955 to 1958, extensive compaction trials were carried out by the
Keller Company to establish the design criteria for the foundation of the
Aswan High Dam (Sad al-Ali) now retaining Lake Nasser in Upper Egypt.
The effect of vibro flotation performed under water in hydraulically placed
fine to medium dune sand was investigated and compared with the results of
compaction by blasting. It was found that densification of the sand by vibro
compaction was superior to that by blasting (Figure 2.14), and the Board of
Consultants for the Sad al-Ali Commission, led by Terzaghi, recommended
compacting approximately 3.4 million m 3 of dredged sand through 35 m of
water under the core of the dam by this method. The Suez crisis of 1956 and
the political tensions thereafter rendered the financing of the project difficult
and prevented the contract award to an originally favored German construction consortium. The gigantic project was finally financed and built by the
Soviet Union, and purpose-built Russian vibrators were used to compact the
sand from 1965 to 1967. Apart from the information that these machines
were operated at 1750 rpm, no other characteristics became known, nor did
the equipment appear again on the international market.
Of similar scale was the foundation work carried out in 1960–1963 for
the Usinor steel works at Dunkirk in France. The subsoil consisted of alluvial
fine sands to a depth of up to 30 m, frequently interspersed by silt and clay
layers, occasionally even peat. Stiff clay followed below requiring relatively
deep embedment of an alternative piled foundation. The economical and
practical advantages of a vibro compaction solution convinced the client to
follow the recommendations of its foundation consultant, Kerisel, for shallow foundations on vibro-compacted sand, in preference to the piled option.
The vibro approach additionally enabled detailed planning to be carried out
after the whole area was first compacted, providing program advantages for
projects of this size. In less than two years, some 480,000 lin.m of compaction were carried out. Where necessary, the cohesive layers were bridged by
large diameter vibro replacement stone columns built by two vibrators (in
places even four) suspended 80 cm apart from each other from one crane
using particularly strong water flush. The works were performed in double