20 Ground improvement by deep vibratory methods
vibro replacement method, whereby fine-grained soils with low water content would be treated without the use of water, and those with high water
content with the help of flushing water. In both cases, the temporary stability of the cylindrical hole created by the depth vibrator was important and
decisive for building a proper stone column of moderate length. The state of
the art which the deep vibratory systems had reached in Germany by the end
of the 1960s is described by Lackner (1966) in his inaugural lecture at the
Technical University of Hannover, underlining the versatility of the method
and its economic importance for the treatment of otherwise unsuitable soils.
With the increasing usage of the method, particularly in fine-grained
soils, occasional failures and setbacks forced the engineers to think more
about the limitations of the stone column method. It was realized that
cohesive soils with very high water contents and correspondingly low consistencies could not provide strong lateral support for the stone columns. If
the stone columns were placed insufficiently closely packed to each other in
these soft soils, which were frequently interspersed by peat layers, overall
settlements would exceed expectations. In the absence of accepted design
principles for these stone columns which would allow a reliable quantitative settlement prediction, the works on-site were more closely supervised
instead. Besides geometrical measurements of the stone columns, the supervision of their steady and consistent build-up by control and registration
of the energy used during their construction was introduced. These findings were supplemented by other standard in-situ testing methods and load
tests on single columns and column groups. In this way, special contractors
and consulting engineers collected valuable information on the behavior of
stone columns in different soils, which were very helpful for their further
application. The lack of computational methods, however, was increasingly
considered a shortcoming of this method, but at the same time it represented a challenge for the engineers. Numerous ideas for the design of soil
improvement by stone columns were developed not only in Germany but
also elsewhere when its use spread beyond its borders.
2.4 DEVELOPMENT OF VIBRO COMPACTION
OUTSIDE GERMANY
Steuermann, one of the method’s inventors, had already left Germany a few
years before World War II broke out. A personal contract with the Keller
Company on the usage of certain joint patent rights granted Steuermann
full rights to the method in the United States where he went to live. In 1939,
he published an article in Engineering News Record on the experiences
gained with the method of vibro flotation in compacting sands in Germany.
However, it took almost 10 more years before reliable compaction equipment was built in the United States and the first construction works could
be carried out.
vibro replacement method, whereby fine-grained soils with low water content would be treated without the use of water, and those with high water
content with the help of flushing water. In both cases, the temporary stability of the cylindrical hole created by the depth vibrator was important and
decisive for building a proper stone column of moderate length. The state of
the art which the deep vibratory systems had reached in Germany by the end
of the 1960s is described by Lackner (1966) in his inaugural lecture at the
Technical University of Hannover, underlining the versatility of the method
and its economic importance for the treatment of otherwise unsuitable soils.
With the increasing usage of the method, particularly in fine-grained
soils, occasional failures and setbacks forced the engineers to think more
about the limitations of the stone column method. It was realized that
cohesive soils with very high water contents and correspondingly low consistencies could not provide strong lateral support for the stone columns. If
the stone columns were placed insufficiently closely packed to each other in
these soft soils, which were frequently interspersed by peat layers, overall
settlements would exceed expectations. In the absence of accepted design
principles for these stone columns which would allow a reliable quantitative settlement prediction, the works on-site were more closely supervised
instead. Besides geometrical measurements of the stone columns, the supervision of their steady and consistent build-up by control and registration
of the energy used during their construction was introduced. These findings were supplemented by other standard in-situ testing methods and load
tests on single columns and column groups. In this way, special contractors
and consulting engineers collected valuable information on the behavior of
stone columns in different soils, which were very helpful for their further
application. The lack of computational methods, however, was increasingly
considered a shortcoming of this method, but at the same time it represented a challenge for the engineers. Numerous ideas for the design of soil
improvement by stone columns were developed not only in Germany but
also elsewhere when its use spread beyond its borders.
2.4 DEVELOPMENT OF VIBRO COMPACTION
OUTSIDE GERMANY
Steuermann, one of the method’s inventors, had already left Germany a few
years before World War II broke out. A personal contract with the Keller
Company on the usage of certain joint patent rights granted Steuermann
full rights to the method in the United States where he went to live. In 1939,
he published an article in Engineering News Record on the experiences
gained with the method of vibro flotation in compacting sands in Germany.
However, it took almost 10 more years before reliable compaction equipment was built in the United States and the first construction works could
be carried out.