ORIGINAL PAPER

Terzaghi: back to the future

Opening address to the 2006 IAEG conference

John Burland

Received: 29 October 2006 / Accepted: 25 November 2006 / Published online: 20 January 2007� Springer-Verlag 2007

Abstract Terzaghi is generally acknowledged as the

father of soil mechanics. The paper draws attention to

his appreciation of an understanding of the geological

profile in terms of its engineering significance. His

contribution is considered in terms of the modern

practice of modelling and his own emphasis on the

importance of experience and judgement. The ‘‘geo-

technical triangle’’ is discussed as a useful way of

bringing together the important aspects of the geo-

technical engineer’s work.

Keywords Terzaghi � Geotechnical triangle �Modelling � Engineering judgement

Resume Terzaghi est generalement reconnu comme

le pere de la mecanique des sols. L’article attire

l’attention sur sa demarche d’interpretation d’un profil

geologique en termes de proprietes geotechniques et

consequences pour des travaux d’engineering. Sa con-

tribution est analysee par rapport a la pratique actuelle

de la modelisation, considerant son attachement a un

jugement d’expert eclaire, soutenu par des references

aux retours d’experience. Le « triangle geotechnique »

est presente comme une base utile a la confrontation

des differentes approches necessaires au metier de

l’ingenieur geotechnicien.

Mots cles Terzaghi � Triangle geotechnique �Modelisation � Expertise

Introduction

This paper looks at the development of our knowledge

of ground conditions and their importance for con-

struction. Karl Terzaghi is frequently referred to as the

father of soil mechanics, but he was very much more

than that. If we regard the term ‘‘geotechnics’’ or

‘‘geotechnical engineering’’ as embracing engineering

geology, rock mechanics and soil mechanics, then

Terzaghi is truly the father of geotechnical engineering.

The paper reflects on Terzaghi’s struggles to develop

and establish the discipline, the art and the science of

geotechnical engineering. His influence on our current

thinking is considered in terms of the geotechnical

triangle, which highlights the importance of not only

the individual aspects of ground profile, observed

behaviour and appropriate model, but also the inter-

action between these and well-winnowed experience.

Attention is drawn to the value of the geotechnical

triangle as an educational tool and the importance of

encouraging young people into geotechnical engineer-

ing as a challenging and exciting career.

Terzaghi—back to the future

Terzaghi was borne in Prague in 1883. Dick Goodman

has written a most illuminating and thoroughly

researched narrative of his life ‘‘Engineer as Artist’’.

He does not come across as a very loveable person, but

geniuses seldom do. The late Professor Sir Alec

Skempton knew him well and distinguished between

his professional life (in which he was harsh and brutal)

and his private social life in which he showed intense

interest and charm in his dealings with others.

J. Burland (&)Department of Civil Engineering, Skempton Building,Imperial College, South Kensington Campus,London SW7 2AZ, UKe-mail: j.burland@imperial.ac.uk

123

Bull Eng Geol Environ (2007) 66:29–33

DOI 10.1007/s10064-006-0083-9

Though he read Mechanical Engineering at the

Technical University of Graz he was much more

interested in geology. He was keen on climbing and it

is related that he made every climbing expedition into

a joyous adventure in field geology. He switched to

civil engineering and went to work for a firm special-

ising in hydroelectric power generation. Although his

main activity was in the design of reinforced concrete,

the planning of the structures was of course intimately

involved with geology. Frequently he found the guid-

ance of the expert geologists of the time unhelpful. He

encountered many cases of failure—significantly

mainly due to lack of ability to predict and control

groundwater. Piping failures were abundant and also

slope failures, bearing capacity failures and excessive

settlements.

Recognising the obvious influence of geological

factors he concluded that it was necessary to collect as

many case records as possible so as to correlate failures

with geological conditions. It is well known that he

then spent two intense years (1912–1914) in the wes-

tern United States, observing and recording. These

two years ended in disillusionment and depression—of

course compounded by the early part of the First

World War.

The following quote from his Presidential Address

to the Fourth International Conference on Soil

Mechanics and Foundation Engineering sums up his

mood at that time:

‘‘At the end of 2 years I took my bulky collection

of data back to Europe, but when I started sep-

arating the wheat from the chaff I realised with

dismay that there was practically no wheat. The

net result of 2 years of hard labour was so dis-

appointing that it was not even worth publishing

it’’.

So much for geology on its own. So much for precedent

and case histories on their own.

To quote Goodman, the problem lay in the fact that:

‘‘.... the names geologists give to different rocks

and sediments have developed mainly from a

scientific curiosity about the geologic origin of

these materials, whereas Terzaghi was aiming

towards discerning the differences in their engi-

neering properties’’.

Shortly after his appointment to the Royal Ottoman

Engineering University in Constantinople in 1916,

Terzaghi began to search the literature for insights into

the mechanical behaviour of the ground. He became

increasingly frustrated. What he witnessed was a steady

decline in accurately recorded observations and

descriptions of behaviour from the 1880s. This was

replaced by myriads of theories postulated and pub-

lished without adequate supporting evidence. This

experience must have been uppermost in his mind

when, in his Presidential Address referred to previ-

ously, he stated the following:

‘‘In pure science a very sharp distinction is made

between hypothesis, theories, and laws. The dif-

ference between these three categories resides

exclusively in the weight of sustaining evidence.

On the other hand, in foundation and earthwork

engineering, everything is called a theory after it

appears in print, and if the theory finds its way

into a text book, many readers are inclined to

consider it a law’’.

Thus Terzaghi was emphasising the enormous impor-

tance of assembling and examining factual evidence to

support empirical procedures. He is also bringing out

the importance of instilling rigour. This is often equa-

ted with mathematics but there is at least as much

rigour in observing and recording physical phenomena,

developing logical argument and setting these out on

paper clearly and precisely.

In 1918 Terzaghi began to carry out experiments on

forces against retaining walls. He then moved on to

piping phenomena and the flow beneath embankment

dams. He used Forchheimers flownet construction to

analyse his observations and apply them in

practice—methods which were themselves adapted

from the flow of electricity. We see here the interplay

between experiment and analytical modelling.

Over this period Terzaghi came to realise that

geology could not become a reliable and helpful tool

for engineers unless and until the mechanical behav-

iour of the ground could be quantified—this required

systematic experimentation. On a day in March 1919,

and on a single sheet of paper, he wrote down a list of

experiments which would have to be performed.

Terzaghi then entered an intense period of experi-

mental work in which he carried out oedometer tests

and shear tests on clays and sands and developed his

physical understanding of effective stress, excess pore

water pressures and time-rate of consolidation—the

birth of Soil Mechanics.

To make headway with modelling the consolidation

phenomenon analytically, he turned to the mathemat-

ics of heat conduction. Again there is the interplay

between experiment and analytical modelling.

30 J. Burland

123

The geotechnical triangle

Geotechnics is a difficult subject and is regarded by

many engineers as a kind of black art. I used to think

that this was due to the nature of the ground and the

fact that it is a two or even three phase material—much

more complex than the more classical structural

materials of steel, concrete and even timber.

However, after careful study of the views expressed

by Terzaghi, and from my own experience, I came to

the conclusion that the main problem was due to a lack

of appreciation of the number of aspects that have to be

considered in tackling a ground engineering problem.

Examining Terzaghi’s struggles towards establishing

the subject, it is clear that there are four distinct but

interlinked aspects:

• The ground profile including groundwater condi-

tions

• The observed or measured behaviour of the ground

• Prediction using appropriate models

• Empirical procedures, judgement based on prece-

dent and ‘‘well-winnowed experience’’.

The boundaries between these four aspects fre-

quently become confused and one or more of them is

often completely neglected.

The first three may be depicted as forming the

apexes of a triangle (Fig. 1) with empiricism occupying

the centre (Burland 1987). Associated with each of

these aspects is a distinct and rigorous activity.

(a) The ground profile Establishing the ground

profile is the key outcome of the site investigation. In

this context, the ground profile is the description in

simple relevant engineering terms of the successive

strata together with the groundwater conditions and

their variation across the site. Also it is vital to

understand the geological processes and man-made

activities that formed the ground profile, i.e. its genesis.

I am convinced that nine times out of ten, the major

design decisions can be made on the basis of a good

ground profile. Similarly, nine failures out of ten result

from a lack of knowledge about the ground

profile—often the groundwater conditions.

(b) The observed or measured behaviour of the

ground This activity involves observation and

measurement. It includes laboratory and field testing,

field observations of behaviour including movements,

groundwater flow and the development and extent of

pollution plumes. It certainly includes modern satellite

methods of earth observation.

(c) Appropriate modelling The term modelling is

being used increasingly and the engineering geologist is

very familiar with the process of developing geological

models. Modelling is the process of idealising or

simplifying our knowledge of the real world and

assembling these idealisations appropriately into a

model which is amenable to analysis and hence

prediction of response—to analyse is to idealise.

The modelling process has not been completed until

the response has been validated and assessed. This may

involve a number of iterations. Thus the process of

modelling is very much more than simply carrying out

an analysis. A model can be a very simple conceptual

one; it can be a physical 1 g model or a centrifuge

model; it can be a very sophisticated numerical model.

By using the term ‘‘model’’ we are emphasising the

THE GEOTECHNICAL TRIANGLEALL ASPECTS ARE DISTINCT BUT INTERLINKED

EACH ACTIVITY HAS ITS OWN DISTINCT METHODOLOGY AND ITS OWN RIGOUR

GOOD GROUND ENGINEERING REQUIRES THAT THE GEOTECHNICAL TRIANGLE IS KEPT INBALANCE

ALL ASPECTS SHOULD BE PROPERLY CONSIDERED

GROUNDPROFILE

OBSERVEDBEHAVIOUR

APPROPRIATEMODEL

PrecedentEmpiricism

Well-winnowedexperience

Geological or Man-made ProcessesGENESIS

Groundexploration

and Description

IDEALISATION -Conceptual, Physical

or Analyticalmodelling -

VALIDATION

Observation,Measurement,

Lab & Field Testing

IdealisationValidation

aV

lidationIdealis

ta ion

Fig. 1 The geotechnicaltriangle

Terzaghi: back to the future 31

123

idealisation process and de-mystifying the analytical

process. The geotechnical triangle helps in this.

(d) Empirical procedures and experience With

materials as complex and varied as the ground,

empiricism is inevitable and it is (and will always

remain) an essential aspect of geotechnical

engineering. Many of our design and construction

procedures are the product of what I have termed

‘‘well-winnowed experience’’. That is, experience that

results from a rigorous sifting of all the facts that relate

to a particular empirical procedure or case history.

In summary we see that within the geotechnical

triangle (Fig. 1) there are four key aspects, each asso-

ciated with distinct types of activity, with different

outputs. Each activity has a distinct methodology, each

has its own rigour, each is interlinked with the others.

Terzaghi’s approach reveals a coherence and integra-

tion which is reflected in a balanced triangle.

Interaction between geotechnical engineersand civil/structural engineers

There are very real difficulties in communication be-

tween geotechnical engineers and civil/structural

engineers. How often have I heard the anguished cry of

the structural engineer: ‘‘why can’t you simply give me

the spring constants for the foundations’’? I have come

to realise that, at the heart of the problem, there are

profound differences in the approach to modelling the

real world situation (Burland 2006).

For routine modelling the civil engineer specifies the

material and the geometry. The idealisation process is

relatively straightforward. Activity is concentrated at

the right hand corner of the triangle in the analytical

process which gives a false idea of precision. The

geotechnical triangle helped me to realise what was

going on and to explain to civil engineers what it is that

we geotechnical engineers are doing.

Consider the example of a civil engineer working on

an ancient building. Figure 2a shows an isometric of

the West Tower of Ely Cathedral which was strength-

ened in 1973/1974 as described by Heyman (1976).

Figure 2b shows the geotechnical triangle but with

some descriptions changed to represent the key activ-

ities undertaken by the structural engineer.

For the ground profile at the top of the triangle we can

insert the structure of the building and its materials. To

establish these requires the most careful examination

and investigation. As with the ground, small disconti-

nuities and weaknesses can play a major role in deter-

mining the overall response. It is also vital to establish

the way the building was constructed and the changes

that have taken place historically—we might call this the

genesis of the building and it is analogous to the geo-

logical processes that have formed the ground profile.

At the bottom left of the triangle are the properties

of the materials and the observed behaviour of the

building. This aspect requires observation, field mea-

surement, sampling and testing. At the bottom right of

the triangle there is the need to develop appropriate

predictive models that take account of the form and

structure of the building, its history, its material prop-

erties and known behaviour—an almost identical

requirement for the ground.

There is a whole spectrum of models that can be

developed, ranging from the intuitive and conceptual

right through to highly sophisticated numerical models.

The key is to appreciate the inevitable idealisations

that have to be made and the limitations that they

impose. Finally, as in ground engineering, well-win-

nowed experience is of supreme importance and well-

documented case records are invaluable.

It is evident from the foregoing that, even if engi-

neers were in possession of unlimited analytical power,

the uncertainties in both the soil and the structure are

so great that precision in the prediction of behaviour

would be unlikely to improve significantly. As in so

many fields of engineering, modelling is only one of the

many tools required in designing for soil-structure

interaction. In most circumstances the real value of

modelling will be in assisting the engineer to place

bounds on likely overall behaviour, in understanding

the mechanisms of behaviour and in beneficially

modifying that behaviour if necessary.

Education matters

The geotechnical triangle was originally conceived as

an educational aid—as a means of illustrating to stu-

dents and practising engineers the distinctive activities,

and their interactions, involved in geotechnical engi-

neering.

The triangle illustrates the way that the scientific

method can be applied when using observations,

measurements and experience in the formulation of

predictive models. It has also proved valuable in

developing balanced syllabuses for teaching various

aspects of geotechnical engineering. Students get very

confused when dealing with results that may be based

on experiment, others that may be essentially empirical

and still others that are based on analysis of an idea-

lised model. The geotechnical triangle serves to

develop confidence in the interactions between these

distinct methodologies.

32 J. Burland

123

It is important to ensure that rigour is retained

in all the distinctive activities, that they are kept in

proper balance and that the interactions between

them are clearly understood (see also Fookes

1997).

Changing the public perception

‘‘Civil Engineering...see boring’’

This statement is from a well-known British telephone

directory and I am afraid is an only too accurate per-

ception of the general public of engineering.

There are many reasons for this but a major one is

that we fail to convey to the public, and to children in

particular, the reality of what working as a geotechni-

cal engineer really involves. Most construction projects

are unique, each offers very special challenges from

conception, through planning and design and then in

construction. Overcoming these challenges can be very

demanding, requiring ingenuity, determination, clear

thinking and many other human attributes.

Yet we present our projects in an unbelievably bland

way. Our technical papers do not properly reflect the

challenge and drama of our work. The perception is

projected that we turn a handle and out pops another

tunnel or dam. It is my experience and belief that the

public, and young people in particular, relate very strongly

to the drama of overcoming adversity, dealing with the

unexpected, responding to challenges and set-backs.

If we start to show more openly the real challenges

of geotechnical engineering as it interfaces with

Mother Nature, I believe that our public profile will

rise and our profession will be seen to be the challenge

and responsibility that it really is. In this way we can

attract the right sorts of young people to it.

Far from being boring, geotechnical engineering is

creative, challenging, has its struggles and very real

human dramas. The responsibilities that we carry are

immense. We are serving communities and working

with our fragile natural environment.

We need to convey this to our students, to the gen-

eral public, and to young people in particular. We must

bring our profession alive to them as it truly is for us.

References

Burland JB (1987) The teaching of Soil Mechanics: a personalview. In: Proceedings of the 9th European conference onsoil mechanics and foundation engineering, Dublin, vol 3, pp1427–1447

Burland JB (2006) Interaction between structural and geotech-nical engineers. Struct Eng April:29–37

Fookes PG (1997) Geology for engineers: the geological model,prediction and performance. QJEG 30:293–424

Heyman J (1976) The strengthening of the West Tower of ElyCathedral. Proc Inst Civ Eng 60:123–147

Fig. 2 a The West Tower of Ely Cathedral (after Heyman 1976).b The geotechnical triangle adapted for the stabilisation of anhistoric building

Terzaghi: back to the future 33

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