Brief
history of Swedish Soil Mechanics
Introduction
Geotechnical engineering in Sweden has a long tradition, dating
back to the work of such outstanding engineers and scientists
as Albert Atterberg, John Olsson, Wolmar Fellenius, Sven Hultin
and Walter Kjellman. The "Geotechnical Commission of
the Swedish State Railways" was instituted in 1913 because
of repeated landslides along the main railroad lines and can
be regarded as one of the milestones of modern soil mechanics.
Landslide at Vita Sikudden on 1 October 1918
The
term "geotechnics" (Swedish geoteknik) was
coined by the Commission. The Geotechnical Commission worked
under the leadership of Wolmar Fellenius, professor at the
Royal Institute of Technology in Stockholm, and presented
its report in 1922. The Commission investigated more than
300 embankment failures and land slips. The use of different
field and laboratory investigation methods was discussed.
In the report the following closing remarks were made:
 |
"The
Committee calls special attention to the fact that in
several cases it is not yet possible to exactly determine
the conditions of balance in loads on weak ground. By
means of some examples the Committee shows that the demand
for absolute safety is not defensible financially, and
roughly estimates the costs of similar measures on the
system of state railways to rather more than less than
one hundred million Swedish crowns. At such places where
there is a risk, but where to ensure complete security
is not within reason on account of the expense, the Committee
considers it better to endeavour to eliminate the risks
of railway disasters, and this can be done by introducing
effective guard arrangements, especially the automatic
warning system. The Committee lastly calls attention to
the fact that the solution of the geotechnical question
lies in a considerably deeper and more extensive study
of the same, and emphasizes the wish that the building
department of the state may arrange a special medium for
geotechnical investigation." |
| Report
of the Geotechnical Commission of the Swedish State Railways
in 1922 |
Besides
the Swedish Geotechnical Commission, a special Harbour Committee
was set up in Gothenburg in 1916 because of the failure of
several quays.
Failure of the Stigberg quay in the harbour of Gothenburg
in March of 1916
The
analysis of this slide, which was performed under the guidance
of Sven Hultin and Knut Pettersson, resulted in the development
of the "Swedish Slip Circle Method". As was usual
at that time, the shear strength of the clay was expressed
as a friction angle. The back-calculation gave a value as
low as 9 degrees.
"Swedish Slip Circle Method" developed by
the Geotechnical Commission
The
Geotechnical Department of the National Swedish Road Authority
was started as early as 1936 under Dr. Walter Kjellman, and
was reorganised as the Swedish
Geotechnical Institute in 1944. The Swedish
Geotechnical Society was founded on February 27, 1950.
The Swedish Geotechnical Institute plays an important role
in the practical application of research and innovative foundation
methods. During its 50 years of existence, SGI has been the
breeding ground for many geotechnical engineers who have since
contributed to the progress of Swedish geotechnical knowledge.
In 1959, the Swedish
Commission on Pile Research was created.
Geotechnical
investigation methods
Swedish geotechnical engineering has made significant contributions
to various areas of soil mechanics and foundation engineering.
The investigations of the Swedish chemist Atterberg on the
consistency and classification of clays, the so-called Atterberg
Limit Tests are today used all over the world. The work of
the Swedish Geotechnical Commission on the shear strength
and settlement of clay was also of fundamental importance.
The Swedish fall cone test was developed for determination
of shear strength and sensitivity, Kjellman´s direct
shear apparatus, unconfined compression test and first true
triaxial apparatus are today standard tools of soil mechanics.
Swedish fall cone test device of 1915
The
difficult geotechnical conditions in Sweden, with deep deposits
of soft, sensitive clay required to the development of innovative
geotechnical field tests, including the Swedish weight sounding
method, the first vane test equipment constructed in 1919,
Kjellman´s Iskymeter and the static cone penetrometer
of 1948, the Swedish Standard Piston Sampler etc.
Swedish Weight Sounding in early 1920
Piling
methods
Historically, the location of cities was often decided by
good communication links (by sea, rivers or roads) and from
a military, strategic viewpoint. In those areas, the geotechnical
conditions were often less than satisfactory and buildings
had frequently to be supported by piles. Also, defence structures
and harbour facilities had to be provided with foundation
support. It is thus not surprising that piling technology,
using driven timber piles or hand-excavated and refilled shafts
were used at an early stage. Driven piles were installed using
a hammer, which was lifted by hand.
Based on the experience from the shipping industry, rope-lifted
hammers were introduced, which facilitated the installation
procedure and made it possible to use horse-driven pile hammers.
The first "modern" pile driving equipment was developed
by the famous Swedish inventor Christoffer Polhem already
in 1740. As a result of the industrial revolution, the first
steam-driven pile hammer became available during the end of
the 19th century. These were gradually replaced by diesel
hammers, and later by drop
hammers.
Timber piles were the
most common foundation method for buildings on soft clay deposits.
As long as these untreated piles were embedded in clay deposits
and remained below the ground water level, they performed
very well. Due to the uplift of the Scandinavian peninsula
following the recent glacial period (up to several meters
during the past 500 years), the top of many of the timber
piles became exposed to air and started to deteriorate. Many
of the ancient buildings in the Old Town of Stockholm had
therefore to be underpinned during the past 20 years.
As a result of urban development, higher buildings and larger
loads had to be supported on available ground, often with
very poor geotechnical properties. Therefore, longer piles
were needed which could carry higher loads. Towards the end
of the last century, driven steel piles were used and the
first concrete piles were introduced during the early period
of this century. While steel
tube and H-piles were
commonly used in other countries, timber and concrete piles
were the most common deep foundation method for heavy building
loads. The harsh climate with cold winters and the geological
conditions, consisting of very soft clay deposits on stiff
till or rock favoured the development of driven, pre-cast
concrete piles. The first concrete piles were used in Sweden
around 1917. The use of timber piles was prohibited in the
inner city of Stockholm in 1944 and gradually, the pre-casting
technique of concrete
piles developed and became refined. The longest concrete
piles were installed in Gothenburg at the Swedish west coast,
where the soft clay deposits reach a thickness in excess of
100 m.
Besides pre-cast concrete piles also other piling methods
were used at some projects, such as driven, cast-in situ piles
(Franki pile) during
1935, and later bored piles (Benoto
piles).
The Swedish Commission on Pile Research was founded in 1959,
which played an important role in the development of equipment,
design and testing methods. The Pile Commission, which is
still very active, combines the efforts from research at universities,
the Swedish Geotechnical Institute with the practical experience
of contracting and consulting companies. It took an active
role in the development of new codes, which resulted in cost-effective
design methods and more efficient use of driven concrete piles.
In 1968, codes for three classes of concrete piles were introduced.
During that period, the piling rigs were modernised, moving
on caterpillar tracks, and provided with adjustable leaders.
Innovative solutions, such as cost-effective pile
joints, rock shoes and pile monitoring techniques have
contributed to the rapid development of Swedish infrastructure.
The first patents for pile joints of pre-cast concrete piles
were awarded around 1960 (type ABB and Herkules). Swedish
hydraulic pile hammers (type Uddcomb and Banut) were developed,
well as the first pre-stressed pile cushion.
During the 60´s, the first stress wave measurements
were performed on concrete piles, which helped to replace
the crude "piling formulas" (Hiley and Kruger) with
rational driving criteria based on dynamic field measurements.
Stress wave measurements became used more frequently during
the 70´s and helped to optimise the pile installation
process and quality control methods. The first International
Conference on Stress Wave Measurements was arranged by the
Swedish Pile Commission in Stockholm in 1980, the second in
1984.
In 1979, the Swedish Pile Commission issued a code for the
design and installation of bored piles, and suggested methods
for dynamic pre-loading of the bore hole using heavy tamping.
As a result of the need for underpinning work in the Old Town
of Stockholm, different types of small diameter driven piles
(steel tube piles) were developed. These could be driven using
light air hammers.
Stress wave measurements in combination with more sophisticated
analysis methods (CAPWAP and WEAP) helped to advance the understanding
of the pile installation process and the assessment of load
carrying capacity. Soil structure interaction was studied
extensively, and the findings of this research led to new
design concepts, such as "creep piles" (floating
pile rafts, where the load is being shared between the foundation
slab and the piles).
Underpinning methods were further improved and several innovative
pile methods were introduced, such as the Soilex Pile, which
uses an enlarged pile base (Expander body). These new piling
methods were more gentle and could be used even in vibration-sensitive
areas, such as basements of ancient buildings and historic
structures.
The European Federation of Foundation Contractors (EFFC) was
founded in 1989, which since has played an important role
with respect to the development of execution codes for different
deep foundation methods. The Swedish Association of Foundation
Contractors (PEF) represents Swedish foundation contractors
in the EFFC, and was responsible for the development of codes
for driven pre-cast piles.
Soil
improvement methods
As early as 1940, Kjellman developed the cardboard drain and
the vacuum consolidation method.
Principle of the Swedish vacuum method developed by
Kjellman in 1952
The group of capable engineers around Kjellman at the Swedish
Geotechnical Institute, made many valuable contributions to
ground improvement techniques, such as Oleg Wager, the inventor
of the pre-fabricated plastic drain and soil reinforcement
by steel anchors and geotextiles and Hansbo on consolidation
and ground improvement.
First application of "steel-reinforced" embankment,
invented by Oleg Wager in 1966
Different types of vibratory compaction techniques, such as
rollers and vibratory probes have been developed for shallow
and deep densification of granular soils. Today, many of the
soil investigation and foundation methods developed in Sweden
are used throughout the world.
Probably the most important recent development in soil improvement
is the Swedish "lime column method", which was invented
in 1969 by Kjeld Paus. This method has since been further
developed and is today the most widely used method for improvement
of soft, compressible clay deposits. Highly advanced installation
equipment with electronic monitoring systems have since been
developed. Research is carried out under the umbrella of the
recently founded Swedish Deep Stabilization Research Centre,
located at the Swedish Geotechnical Institute.
Swedish
Geotechnical Society (SGF)
The Swedish Geotechnical Society
was founded in 1950, and has more than 600 individual members.
The most important geotechnical event in Sweden is the annual
"Foundation Day" (Grundläggningsdagen), where
different topics of practical importance and interest are
discussed.
"Back to Basics" Topic of the Swedish Foundation
Day 1995
This
annual gathering is usually very well attended. It is complemented
by society meetings, which are arranged by SGF committees,
dealing with geotechnical problems of particular interest
at the time.
SGF, through its committees, works out standards and recommendations
for geotechnical investigations, analysis and design methods.
These and other important documents are published by SGF as
technical reports or information pamphlets. Several of these
reports are published in English.
One of the landmarks of the Swedish Geotechnical Society was
the organisation of the X. International Conference on Soil
Mechanics and Foundation Engineering, which was held in Stockholm
in 1981. In addition, international conferences and symposia
were organised by the Swedish Geotechnical Society, such as
the first European Symposium on Penetration Testing, ESOPT
in 1974, International Conferences on Application of Stress-Wave
Theory, Nordic Geotechnical Meetings etc.
An important objective of SGF is to facilitate interaction
between experienced and young engineers. Scholarships are
awarded annually to outstanding students and researchers at
different levels, encouraging them to visit research institutes,
conferences or interesting projects abroad.
The Swedish Geotechnical Society has close co-operation with
the Nordic sister societies in Denmark, Finland, Iceland and
Norway. New contacts are being taken with the geotechnical
communities in the emerging Baltic states, which share similar
problems as the Nordic countries.
Geotechnical
research
Geotechnical research in Sweden is carried out primarily at
the major technical universities: Royal
Institute of Technology, Chalmers
Univeristy of Technology, Technical
University of Lund, Technical
University of Luleå. In addition, the Swedish Geotechnical
Institute carries out extensive research programmes, being
a link between the research institutions and geotechnical
practice.
In Sweden, there is a long and fruitful tradition of a close
co-operation between scientists, educators, practising engineers,
manufacturers of geotechnical and construction equipment,
clients and authorities. Research in areas of great importance
to society is carried out in Commissions, with the task to
focus research, development and dissemination of information
on specific areas. By these Commissions, the work of which
is financed by government authorities as well as by contributions
from the industry, important contributions have been made
to the development of Swedish geotechnical and foundation
engineering.
The Swedish Pile Commission,
the Land Slide Commission and the Swedish
Vibration Committee are examples of fruitful co-operation
between different sectors of society.
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