arte e ciencia no sub solo - ralph peck

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ART AND SCIENCE IN SUBSURFACE ENGINEERING 
by 
RALPHB.PECK 
Subsurface engineering is an art; soil mechanics is an engineering science. This distinction, 
often expressed but seldom fully appreciated, must be understood if we are to achieve progress 
and proficiency in both fields of endeavour. 
Almost every week the journals of foundation and earthwork construction describe at 
least one failure. Yet, year after year, more and more workers have been devoting their 
attention to soil mechanics and have created a literature of impressive scope and extent. 
Can there be, as some people have intimated, a correlation, a causal relationship, between the 
growth of soil mechanics and the number of foundation and subsurface mishaps? 
To be sure, the high incidence of failures or of unexpectedly costly jobs is a consequence 
partly of the accelerated pace of construction, and partly of the fact that soil mechanics has 
opened the door to more complex and more daring jobs than would have been considered 
feasible a few years ago. Nevertheless, a disturbingly large residue of costly and unfortunate 
incidents remains to be explained, even in circles where soil mechanics is by no means unknown. 
This situation may have arisen out of our failure to discriminate between art and science. 
In an age of scientific marvels, civil engineers have lost sight of the accomplishments of the 
artist in his profession. We would do well to recall and examine the attributes necessary for 
the successful practice of subsurface engineering. These are at least three: knowledge of 
precedents, familiarity with soil mechanics, and a working knowledge of geology. 
Of these, a knowledge of precedents is by far the most important. Two centuries ago, 
engineers were constructing widespread systems of canals involving deep cuts in difficult 
ground; a century ago railway engineers drove large and long tunnels in water-bearing sands 
below ground-water level. These and many other works were completed, with dilliculty to be 
sure but nevertheless successfully, without benefit of modern soil mechanics. The engineers of 
those days had little to guide them but experience-not only their own experience, of course, 
but also that of their contemporaries and, to the extent it had been recorded, of their pre- 
decessors. If these men could accomplish so much only on the basis of experience and their 
own native intelligence, surely experience is a priceless asset of the subsurface engineer even 
today. 
The heritage from the past every engineer may have by the simple act of reading. But 
this heritage, although vital to his background, is necessarily second-hand. To it, every 
engineer must add his own, first-hand experience before he can attain professional competence. 
Yet the mere passage of the years of professional life does not guarantee the kind of experience 
needed to develop the artistry of the proficient subsurface engineer. The experience must 
contribute to professional growth; it must be carefully sought and selected. The young man 
must see that he is assigned under competent supervision to work of significance, of variety, and 
of increasing difficulty and responsibility. Otherwise, after 20 years of engineering activity 
he may not be able to claim 20 years of experience, but only that he has acquired one year’s 
experience twenty times. 
The development of a background of personal experience is not, then, a passive activity. 
It requires conscious and persistent effort. It requires the ability to observe what is happening, 
to retain the observations, and to discriminate among items that are significant and irrelevant. 
The ability to observe is by no means inborn. Many a young man, sent to make his first 
field inspection, returns to the office to discover that he cannot remember the details of much 
that he saw. His embarrassment may lead him to believe that he lacks a sixth sense that some 
engineers must possess, so he may avoid future assignments of this sort. If he follows this 
60 
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ART AND SCIENCE IN SUBSURFACE ENGINEERING 61 
course, his future as an artist in the practice of subsurface engineering is doomed; he has cut 
himself off from his own experience. On the other hand, he may seek to develop the art of 
observation and retention. In his hotel room in the evening he sketches from memory the 
details of the bracing of an open cut he just inspected. He discovers that he cannot remember 
certain details; next day he corrects his sketches. He cultivates the habit of keeping a 
professional diary with brief but accurate descriptions of design and construction procedures. 
AS he cultivates these habits he discovers that his powers of observation and retention become 
more acute; he begins to know what tolook for and what to ignore; he is on the way to be- 
coming an experienced individual. 
Once the ability to make the most of experience has been successfully cultivated, even the 
young engineer can become truly experienced in surprisingly few years. Personal experience 
is not a matter of elapsed time but rather of the intensity with which the experience is pursued 
and absorbed. 
Finally, the young subsurface engineer should seek experience with variety: in the field, 
where he can observe at first-hand the methods and consequences of construction operations 
in many types of soils and rocks; in the design ofice, where he can learn the peculiar problems 
of the designer and can come to appreciate the interrelation between design and construction: 
and even in research, where he can learn how the frontiers of knowledge are being pushed back 
and can form a judgment about the difference in mental attitude required for successful re- 
search as compared to successful engineering practice. 
No man can hope to be truly an artist in the practice of subsurface engineering without a 
rich background of personal experience, or without an adequate knowledge of the experiences of 
his contemporaries and predecessors. Therefore, experience is given first place among the three 
essential attributes. Nevertheless, soil mechanics and geology are hardly less important. 
What, precisely, is the function of each of these disciplines in the art of subsurface engineering? 
Soil mechanics, in the first place, provides qualitative and quantitative data concerning 
the stress-strain-time characteristics of earth materials. This knowledge gives us a feeling 
for the behaviour of soils, under idealized conditions, which may guide us in anticipating 
behaviour under the more complex conditions in the field. Similarly, the theories of soil 
mechanics provide insight into behaviour under simple, ideal conditions. Yet, of what 
practical value is this information ? 
First and foremost, these aspects of soil mechanics form a framework that helps engineers 
to organize, interpret and evaluate experience. The miscellaneous collection of facts ac- 
cumulated during a professional lifetime would be of no value if it could not be organized and 
brought to focus on new problems. Before soil mechanics there was no rational framework to 
serve this purpose. As a result, even the most renowned engineers occasionally made serious 
errors because they tried to apply what appeared to be a precedent to a situation where some 
vital factor was essentially different from those controlling the behaviour of the precedent. 
All too often, generalizations were drawn from experiences in a single soil deposit; there were 
no index properties to warn that the deposit might, in fact, be unusual or unique with respect 
to some controlling characteristic. With no knowledge of the effect of seepage forces, failures 
were often attributed to the type of soil rather than to relevant hydraulic conditions. Soil 
mechanics brought order out of this chaos. Each experience that comes to the attention of an 
engineer can now be examined and categorized asto type of material, and as to its relationship 
to the stress-strain-time characteristics of the appropriate types of soil. It can also be 
examined in relation to theoretical concepts. The experience may fit nicely into the frame- 
work of soil mechanics, or it may appear to be an exception. In either event, the body of 
knowledge known as soil mechanics provides a convenient and logical basis for preserving the 
essential features of the experience. In short, soil mechanics has made it practicable to 
utilize the vast amount of precedent and experience already accumulated and still to be 
obtained. Its importance in this connexion cannot be overemphasized. 
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62 RALPH B. PECK 
The everyday procedures now used to calculate bearing capacity, settlement, or factor of 
safety of a slope, are nothing more than the use of the framework of soil mechanics to organize 
experience. If the techniques of soil testing and the theories had not led to results in accord 
with experience and field observations, they would not have been adopted for practical, 
widespread use. Indeed, the procedures are valid and justified only to the extent that they 
have been verified by experience. In this sense, the ordinary procedures of soil mechanics are 
merely devices for interpolating among the specific experiences of many engineers in order to 
solve our own problems which we recognize to fall within the limits of previous experiences. 
In addition, however, the subject of soil mechanics provides the means by which we can 
often go beyond the limits of our own experience or that of others. It points the way to new 
solutions of old problems, or to the solution of previously unsolved problems. It is, in this 
respect; a means for extrapolating our experience. Of course, such extrapolation involves a 
measure of uncertainty until the pertinent experience becomes available. But even here, soil 
mechanics guides us as to what we should observe to check our procedures as we execute the 
work. .‘I:; 
These are the vital functions of soil mechanics. They fully justify all the attention.that 
has been paid to the subject. But it is clear that soil mechanics is no substitute for ek+ 
perience. Its.great role is in making experience more meaningful. .’ 
Geology, the’third ingredient, is as basic to subsurface engineering as is soil mechanics, 
Possibly its most significant role is to make us aware of the departures from reality inherent in 
our simplifying assumptions. Whereas the theories and computational procedures of soil 
mechanics would be impracticable without simplifying assumptions regarding the properties 
of the subsurface materials, nature is not simple. The geology of a site must be understood 
before any reasonable assessment can be made of the errors involved in our calculations or 
predictions. Indeed, in some instances the geologic structure or the results of geologic pr& 
cesses may completely override all considerations of soil mechanics. The nature and orienta- 
tion of the relict joints in a residual soil may govern the stability of the sides of an excavation 
for a foundation, quite irrespective of the properties of the soil between the joints and quite at 
variance with predictions of theory based on assumptions of homogeneity. 
Geology also, like soil mechanics, provides a means for correlating our experience, but on a 
regional or physiographic basis. Regional studies of foundation conditions have proved 
very useful to the practising engineer. They pertain to areas in which experiences should be 
similar; hence, the conclusions are valid only if the physiographic units have been established 
upon a sound basis of geologic similarity. 
Finally, whether we realize it or not, every interpretation of the results of a test boring and 
every interpolation between two borings is an exercise in geology. If carried out without 
regard to geologic principles the results may be erroneous or even ridiculous. Conversely, if 
done with a keen perception of local geologic conditions, the results are likely to be much more 
reliable. It is hardIy necessary to labour the point that intelligent subsurface exploration is 
impossible without a working knowledge of geology. 
The highest level of artistry in the practice of subsurface engineering is found in the man 
who, in addition to a sound training in civil engineering, has cultivated a background of 
pertinent experience, correlated and extended by means of the two sciences-soil mechanics 
and geology. The background of the expert in the practice of subsurface engineering and that 
of the expert in soil mechanics, then, are by no means the same. The distinction is important. 
Possibly it can best be illustrated by an analogy to the practice of medicine and to 
medical science. * The analogy is especially instructive because the practice of the art of 
medicine is almost everywhere considered to be an endeavour of professional stature. 
* This analogy was first suggested by Mr M. M. FitzHugh, who had observed Dr Terzaghi’s approach to 
problems of design and construction of an unprecedented shipway for which Mr FitzHugh was responsible 
(see Trans. Amer. Sot. civ. Engrs, 112:298-324.) 
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ART ANIJ SCIENCE IN SUBSURFACE ENGINEERING 63 
When we are ill, we visit the doctor with the expectation that he will diagnose our illness 
correctly and, if possible, provide a treatment that will cure us. He begins his investigation 
with questions about our history, our family, and our environment, and about our recent 
symptoms. Then he passes to a qualitative physical examination. He thumps our chest and 
listens to the sound, he uses his stethoscope to hear further sounds, he taps our knees with a 
rubber mallet to ascertain our reactions, he holds down our tongue and looks down our throat. 
None of these activities can be considered scientific. They do not provide numerical vaIues 
of any physical quantities that can be used directly in diagnosis, but they provide qualitative 
data that have been correlated by experience with the behaviour of thousands of 
individuals. 
Next, the physician performs or requests the performance of certain physical tests that 
provide quantitative data. Some of these tests are routine, such as the determination of our 
weight, height and blood pressure. Some, such as blood counts and sedimentation rates, 
must be done by trained technicians. A few may require higher degrees of technical training, 
such as the performance of basal metabolism tests. These tests are based upon scientific 
studies but they are not in themselves scientific. They provide numerical values which have 
much the same function as index properties in soil mechanics. Their usefulness lies in the 
correlation of the numerical values with the behaviour of many human beings. 
After this routine the doctor may be ready to make his diagnosis. This is the first import- 
ant result for which we have retained his services. We should like the diagnosis to be correct. 
We may have chosen a particular doctor because of his reputation as an expert diagnostician. 
But what makes the difference between the expert diagnostician, the artist in his profession, 
and the less talented man? 
The true artist in his profession considers all the information he has obtained, digests and 
studies it in the light of his training and experience, and arrives at a diagnosis which he regards 
as a tentative hypothesis regarding our ailment. It is obvious that the more varied personal 
experience the doctor has had, the better are the chances that he can recognize our ailment. 
Furthermore, if he conscientiously studies current medical literature, he is better prepared for 
the diagnosis. If he is well versed in medical science and in the academic studies he pursued 
as a younger man,this, too, will add to his skill as a diagnostician. Yet, we recognize that the 
simple addition of all these attributes does not produce the true artist. The same experiences 
are more meaningful to some individuals than to others. The artist may notice and be in- 
fluenced by intangibles of which the ordinary practitioner may not even be conscious: the 
colour of our skin, the way an eyelid droops, the way we walk as we enter his office. The sum 
total of all these impressions contributes to the diagnosis. 
But the diagnosis is at best only a hypothesis that must be tested. The artist in the medical 
profession accomplishes this by prescribing a treatment. If his diagnosis is correct, the 
treatment may result in a cure. If his diagnosis is not correct, the treatment is designed to 
produce reactions that in themselves will lead to a better diagnosis. So, the doctor gives his 
orders and his prescription, and tells us to return after a week. If we are faithful and do so, he 
inquires about our feelings and reactions, he may repeat some of his qualitative tests and he 
may even repeat some of the quantitative tests. On the basis of the second examination he 
may conclude that his tentative hypothesis was in error, but if he has planned his treatment 
well, our reaction has provided him with the information for a much better diagnosis. He may 
now be able to prescribe with greater confidence a treatment that will lead to a cure. If our 
case is particularly difficult, he may have to follow his second hypothesis with a third or 
a fourth, always refining the treatment and studying the reaction until our response is what he 
anticipated. He is then finally sure of his diagnosis. 
Of course, the true artist is more likely to arrive at a correct diagnosis the first time or to 
arrive more quickly at a correct diagnosis than his less expert colleagues. But the method is 
valid even for the man of lesser ability, provided of course that we survive the period of 
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64 RALPH B. PECK 
experimentation. If our illness is critical, we will be well advised to consult the best possible 
diagnostician in the hope that he can arrive at the proper solution in time. 
The similarity of this procedure to the observational or learn-as-you-go method of the 
subsurface engineer is obvious. In dealing with the foundations for earth dams, and with 
difficult foundation or excavation problems, the subsurface engineer has, indeed, found the 
observational procedure to be his most powerful tool. 
Let us now look briefly at medical science. It may surprise us to find that many of the 
outstanding workers in medical science are not M.D.‘s at all, but Ph.D.‘s and D.Sc.‘s in a 
variety of fields. They may be biologists, biochemists, physical chemists, psychologists or 
even solid state physicists. When we look, for example, at the broad attack on the cancer 
problem today, we see scientists of all types and technicians in all branches of science working 
individually or as members of teams on a variety of problems that may seem only remotely 
related to cancer. Many gifted and highly trained people are investigating problems that 
interest them from the scientific point of view. Yet these people are rarely medical practi- 
tioners. They might be very poor diagnosticians. Indeed, many of them could not obtain 
the necessary licence to practice the art of medicine. But they contribute mightily to the 
body of medical science that filters into practice as its implications become of practical value. 
The medical practitioner is not uneducated in science. He has a background of courses in 
anatomy, physiology, chemistry, physics, and many other scientific subjects. A large part of 
his education is built on the results of medical science, but he is not a scientist and his scientist 
friends are not practitioners of the art of medicine. 
In the application of the observational procedure the engineer relies heavily on the scientific 
background to which he has been exposed in mechanics and hydraulics as well as soil mechanics 
and geology. He may in some instances not perform a single calculation based upon theory, 
but the theoretical relationships among the variables associated with different phenomena have 
become ingrained in his intellect by long study and have in a sense become second nature. He 
also brings to bear his broad knowledge of construction and design practices, and his skill and 
knowledge in the interpretation of geologic phenomena. All these aspects of his background 
are brought to focus on the individual problem with which he deals. He recognizes as does 
the medical doctor that no two foundation or earthwork jobs are identical any more than any 
two human beings are identical. He must know what is common about the properties of soil 
deposits and he must know what is specific to a particular deposit. His skill in planning the 
exploratory programmes and in devising field observations that will lead to better hypotheses 
constitutes one of his most valuable assets. 
Although in his attack on a problem the subsurface engineer makes liberal use of soil 
mechanics and geology, his professional work is neither soil mechanics nor geology. It is a 
synthesis of these and a host of other aspects of his background without which he could not 
successfully practice the art. 
The expert in the engineering science of soil mechanics, on the other hand, is in fact a 
scientist. He may be a theoretician interested in the behaviour of idealized materials. He 
may be an experimentalist vitally concerned with the relationships among the variables that 
seem to control the physical properties of soils. He may be intrigued by the forces that act 
between soil particles. He may be a physical chemist, a pedologist, or a mechanical engineer. 
His contributions to soil mechanics may find application in the art but they do not constitute 
the practice of engineering. The distinction is as clear as that between the science and the 
art of medicine. 
It is apparent that a high degree of professional attainment in the science of soil mechanics 
is no warranty of success in the practice of the art of subsurface engineering. Conversely, 
some of the most expert practitioners in the art of foundation engineering would be at a loss 
to make a significant contribution to soil mechanics. Occasionally the same individual 
combines talents in both the science and the art. Such individuals are rare, but soil mechanics 
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ART AND SCIENCE IN SUBSURFACE ENGINEERING 65 
might not have been born or found application had not Terzaghi been of this dual character. 
Certainly, Terzaghi has always clearly recognized the distinction between the science of soil 
mechanics and the art of subsurface engineering. 
The analogy that has been developed has implications with regard to engineering education. 
There is today a strong and even a growing feeling that engineering education should consist 
of education in engineering science. Soil mechanics fits into this category. On the other 
hand, the art of subsurface engineering may be relegated to a seminar or may not be taught at 
all. Some people in academic circles are of the opinion that an art cannot be taught. 
The medical profession does not share this delusion. It believes that the art of medicine 
can be taught. It sees that its students obtain good backgrounds in science and in laboratory 
techniques. But it also trains its novices in the accumulated empirical knowledge of their 
profession and in the art of diagnosis and clinical practice. It does not by any means believe 
that classroom training alone can make a good diagnostician but it recognizes that the approach 
to the problems of diagnosis is a separate and important aspect of medical education. It 
knows that training in sciencealone could not possibly produce men capable of becoming 
expert in the art of the profession of medicine. 
Indeed the medical profession is not greatly concerned with the training of medical scien- 
tists. The majority of medical scientists are trained not in medical schools but in universities, 
usually colleges of liberal arts and science. While there is much cross-fertilization of ideas 
among workers in medical science, training in this field is essentially training in some branch 
of science. 
There is no point in debating the relative importance of the worker in the science of soil 
mechanics and of the practitioner of the art of subsurface engineering. Both belong to worthy 
professions, but these professions are fundamentally as different as are the art and science of 
medicine. The increasing importance of science and the increasing adaptation of science into 
the art of subsurface engineering fully justify the training of engineering students in soil 
mechanics. But the practice of the art of foundation engineering requires far more than a 
background in soil mechanics. Much of this background can and should be taught at the 
college level. A working knowledge and an appreciation of geology are essential. Some 
concept of the process of design, possibly obtained in courses in steel or concrete design, is also 
a necessary ingredient. Furthermore, the essence of the observational procedure can be 
taught and can be illustrated by effective examples. If soil mechanics is substituted for the 
whole of the broader aspects of this professional background, the education of the subsurface 
engineer is poor indeed. 
The real artist in the practice of foundation engineering is one of the finest products of the 
engineering profession. He is today a rare individual. It is as absurd to believe that he will 
develop automatically, provided he is thoroughly trained in soil mechanics while in college, as 
it is to believe than an expert medical doctor will develop automatically if a man is taught 
only medical science. 
It is granted that the scientific aspects of engineering subjects can be learned most readily 
at the college level whereas experience accumulated through the years adds increasingly to a 
man’s professional ability. But unless our educational system provides a knowledge of the 
other disciplines that also contribute to proficiency in practice, and unless the engineering 
student is given guidance as to what experience he should seek and how to utilize this exper- 
ience, he may not develop his potentialities. 
Finally, it is suggested that research in subsurface engineering need not be confined to soil 
mechanics. There is room for research in a broader sense, into the interrelationships among 
soil mechanics, geology and engineering practice, and into the techniques for most success- 
fully attacking problems made especially difficult by the complexities of nature. The current 
emphasis on research in soil mechanics as such only demonstrates the necessity for increased 
attention to the other ingredients for successful practice. 
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66 RALPH B. PECK 
Is it true, then, that there is a causal relationship between the growth of soil mechanics 
and the number of foundation and subsurface mishaps ? Certainly it is, to the extent that soil 
mechanics is considered a substitute for the whole art of subsurface engineering. As long as 
engineers are content to make recommendations for design and construction solely on the basis 
of borings, soil tests, and calculations; as long as virtuosity in theory is considered more praise- 
worthy than artistry in practice; as long as education glorifies mathematical science to the 
exclusion of our heritage of empirical knowledge; as long as research at the desk or in the 
laboratory is regarded as being of a higher order than that pursued in the field-as long as these 
conditions exist or to the extent that they exist, the practice of subsurface engineering may 
suffer at the hands of soil mechanics. Let us hope that this is a passing phase in a transition 
from pure empiricism to the highest professional artistry, in which soil mechanics may play its 
proper, necessary, and worthy role. 
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