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NATIONAL ｾｅｓｅａｒｃｈ COUNCIL OF CANADA
ASSOCIATE COMMITTEE ON SOIL AND SNOW MECHANICS
TECHNICAL ｾｅｦｵｏｒａｾｄｄｍ NOa 11
PROCEEDINGS OF 1948
CIVILIAN SOIL MECHANICS CONFERENCE
OT'rAVvA9 CANADA
Section No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 TABLE OF CONTENTS Title Foreword Introductory Remarks
General Statement on Second International Conference on Soil Mechanics and Foundation Engineering, Rotterdam, June,
1948
Laboratory Investigations Field Investigations
Problems of Road and Runway Construction
Tour of Montreal Road Site Earth Pressure, Stability and
Displacement of Retaining Structures
Pile Foundations and Pile Loading Tests
Stability and Deformation of Earth Structu res
Informal Evening meeting
Foundation Pressure and Settle-ments of Build ings on
Footings and Rafts
Improvement of the Mechanical Properties of Soil
Gro undwat er- Protil.e.ns Subjects of a General
Character
Visit to SolI Mechanics Laboratory
(i)
Page No. 1 2 4 6 12 17 22 23 28 37 41 42 47 52 57 61(ii)
Seot ion
Noo
J Title Page NO.g17 A Physiographic Map of
Southern Ontario 62
18 Reports of Regional Group
Activi ties 65
19 Future Programme of Subcommittee
on Civilian Soil ｍ･｣ｨｾｮｩ｣ｳ 69
20 Canadian Representa.tioh on the
International Society of Soil Mechanics and Foundation
Engine ering 71
21 Concl uding Remar-ks 73
Appendix A = List of 'rhose Attending the 'Conference
Appendix B = Agenda9 1948 Civilian Soil Mechanics Conference Appendix C - Statutes of the International Society of Soil
Mechanics and Foundation Engineering Subject Index
1.
NATIONAL RESEARCH COUNCIL OF CANADA
ASSOCIATE COMMITTEE ON SOIL AND SNOW MECHANICS Proceedings or 1948 Civilian Soil Mechanics Conrerence, Ottawa, 13 - 14 December, 1948.
This is the record or a Conrerence or most or the active Canadian workers in the rield or Soil Mechanics, held in the Seminar Room or the Montreal Road Laboratories or the National Research Councilor Canada, in Ottawa, 13 - 14
December, 1948, under the auspices or the Associate Committee on Soil and Snow Mechanics. The meeting was held at this time or the year in order not to interrere with construction activities and so that all present might hear rram those Canadians who attended the Second International Conrerence on Soil Mechanics and Foundation Engineering, held in
Rotterdam in June, 1948.
A list or those who attended the Conrerence accompanies this report as Appendix A. The material con-tained in Sections 2 - 11 was presented on 13 December and the remainder on 14 December.
Sect ion 2
INTRODUCTORY ｒｅｾｬｬｩｒｋｓ
The Conference was opened by Mr o H o F o ｌ･ｧｧ･ｴｾ
Chairman of the Associate Committee on Soil and Snow ｍ･｣ｨ｡ｮｩ｣ｳｾ
who welcomed those present and explained that the principal function of this ｧ｡ｴｨ･ｲｩｮｧｾ as of the corresponding meeting
last ｹ･｡ｲｾ was to enable Canadian workers in the relatively
new field of Soil Mechanics to meet together to discuss problems and exchange information of mutual interesto
He outlined briefly the work of the National Research Council of Canada and its interest in sponsoring conferences such as this o The work of the Council is carried out by means of Divisions in which active research is ､ｯｮ･ｾ and by Associate CommLtt e e s , The latter perform the function of gathering
together authorities in order to deal with specific problemso The Associate Committee on Soil and Snow Mechanics was
originally formed in 1945 to deal with ｾｨ･ urgent military
problem of the interrelation of the design of military vehicles with ground conditionsv This Associate Cormnittee has now
expanded its activities to related civilian fields of ｩｮｴ･ｲ･ｳｴｾ
and has ｮｯｷｾ ｴｨ･ｲ･ｦｯｲ･ｾ five working Subcommittees to deal with respectively the original ｶ･ｨｩ｣ｬ･ｾｧｲｯｵｮ､ ｰｲｯ｢ｬ･ｭｾ with snow and ices mus ke g , permafrost and civilian soil mechanics0
The last=mentioned Subcommittee was ｮｾｾ･､ at the first annual Civilian Soil Mechanics Conference in April) 19479 and is composed of regional representatives from all across ｃ｡ｮ｡､｡ｾ
and the Chairman and SecretarYn All these representatives were now ｰｲ･ｳ･ｮｴｾ from British ｃｯｬｵｭ｢ｩ｡ｾ the Prairie ｐｲｯｶｩｮ｣･ｳｾ
Torontop Ottawas Montreal and the Maritimes o Each ｲ･ｰｲ･ｳ･ｮｴ｡ｾ
tive is in contact with those per-sons in his particular region who are interested in Soil Me ch anlcs, and contact between the various representatives is maintai ned through the Secretary of t.he Associate Committee in Ott awa , A start has therefore been made to integrate Soil Mechanics work in Canadan and it is hoped this trend will continue to the mutual
benefit of all concerned o
One of the ｭ｡ｮｾ purposes of this Conference was to give those Canadians who attended the recent Second
International Conference on Soil Mechanics and Foundation Engineering at Rotterdam an opportunity to reviewp for the
benefit of those present9 what they saw and heard at the International Meeting Bnd to express their views upon ito
The First International Conference on Soil Mechanics and Foundation Engineering was held at Harvard University in 19369 and a great deal of valuable ｩｮｦｾｔｭ｡ｴｩｯｮ was assembled at that time o The second such conference was postponed due to the war and was only recently held in Rotterdron o Six of
3. those now present were privileged to attend the Rotterdam Conference. These were Dean R.M. Hardy, of the University of Alberta, leader of the Canadian Delegation; Dr. N.W. McLeod of Imperial Oil Limited, Toronto; Mr. Ro Peterson of the P.F.R.A o, Saskatoon; Mr. D.G. Watt of the Hydro Electric Power Commission of-OntaFio, Toronto; and Messrs. F.L. Peckover and WoRe Schriever of the Division of Building Research, National Research Council,Ottawa.
The Chairman announced that the various technical aspects of Soil Mechanics would be dealt with at this
meeting under the general headings used in the Proceedings of the Rotterdam Conference. Reviews of the papers
presented on each topic at Rotterdam would be made by members of the Canadian Delegation and a discussion on each subject would follow the general review.
The agenda of the Conference accompanies this report as Appendix B.
Section 3
GENERAL STATID'lENT ON SECOND
INTERNATIONAL CONFERENCE ON SOIL MECHANICS AND FOUNDATION ENGINEERING, ROTTERDAM, JUNE 1948
by Dean RaMo Hardy
The Second International Conference on Soil Mechanics and Foundation Engineering was attended by close to 600
representatives of some 27 nations. The only major countries not represented were Russia and Germany a Official delegates were in attendance from many governmental, industrial,
professional" educational and research bodfe a , including public works departments, naval? army and air forces, railroad corpora-tions? harbour authoritiesp hydro=electric_power corporations?
contracting firms!) testing laboratoriess> universities and so fortho Active interest in the field of Soil Mechanics and Foundation Engineering by a much wider representation of Civil Engineers and Geologists was evident than is presently the case in Canada.
The seven volumes of the Proceedings of the Conference contain some 400 contributions covering practically all aspects of the field of Soil Mechanics and Foundation Engineering»
together with discussions of many special local problems from numerous parts of the worldo The papers were grouped into 12 sections for the purposes of the Proceedings and this grouping was used as a basis for discussion at the technical sessions of the Conferenceo Single sessions were devoted to a group of two or three sections with the discussion opened by a presentation of a review of the more significant contributions to these
sectionso A highlight of several of the discussion sessions was the brilliant summing up of the present status of knowledge and points of controversy concerning the particular topics
considered by Dro Terzaghi, President of the Conferenceo In contrast to the present practice in Canada, the complete nature of the investigations concerning major projects involVing soil behaviour and also cases of damage due to soil conditions in Great Britain and Europe was most impressiveo In many countries much closer cooperation between geologists and engineers working in the field of Soil Mechanics seems to
exist than is the case in Canada.
In a very interesting contribution by Mro H.Q.Golder of Soil Mechanics ｌｩｭｩｴ･､ｾ Londonl) it is pointed out that a considerable variety of approaches and techniques have been developed in handling soil and foundation problems in various parts of Europe. Difficulties in the mutual exchange of
5.
experience during the period of the war undoubtedly
have accentuated the present situation. However, Mr. Golder draws attention to the fact that these differences are to
a considerable extent due to the local conditions encountered in the various countries. Dr. Terzaghi also drew attention to the existence of a tremendous range of soil types and conditions in various parts of the world, and emphasized that local problems must be solved locally by those
working with particular conditions.
We in Canada, however, are concerned with a
situation which is rather unique as compared to most other national areas in that an exceedingly wide variety of soil types and conditions is encountered in various parts of the country. To illustrate briefly, one need only mention the waterfront conditions on the coasts, the brittle Laurentian clays of Quebec and Ontario, the heavy fissured clays of the Prairies, the sensitive silts of many parts of British Columbia and southern Alberta, the permafrost of the north and the muskeg occurring so widely in both the east and west as well as the north. Moreover, variations of climatic
conditions are not only locally extreme but range from the very temperate to the arctic conditions of the far north. Under these circumstances, the economical solution of our problems in the field of Soil Mechanics and
Foundation Engineering requires an exceptionally wide background and a high degree of proficiency of those working in these fields. However, by the same token, Canadian engineers and geologists are presented with an opportunity, perhaps one might even say a responsibility, equalled in few otber countries of the world to make
significant contributions to the general body of knowledge in these fields.
Section 4
LABORATORY INVEST1GATIONS
(Section II of Rotterdam ｐｲｯ｣Ｄ･､ｩｮｾｾＩ by Dean Ho M Hardy
A total of 50 contributions were sUQmitted in this Sectiono They have been grouped under ｳ･ｶ･ｮｳｵ｢ｾｳ･｣ｴｩｯｮｳ
dealing with the following topicsg general. identification
t est s , consolidation t.est s , triaxial compression te st s , direct shear t.e st s , e l.e ctr-o-iosmosLs and miscellaneous 0 In addition
some 17 papers under aub-is e ct.Lona (cL (d) and (e) of Section I dealing with physical and ｰｨｹｳｩ｣ｯｾ｣ｨ･ｭｩ｣｡ｬ properties of soLls , stress,-,strain r-eLat.Lons , and shearing strength of
ｳｯｩｬｳｾ have a direct ｣ｯｮｾ･｣ｴｩｯｮ with laboratory investigationso
Papers by Winterkornj Grim and several others
dealing with physLco-scnemt cal phenomena associated with soil properties are particularly sLgnLf'Lcant , They demonstrate
the important contribution to the explanation_ of the properties of fine grained soils that is being made through the
application of the fundamental principles of physical chemistry to the pr'o bLem ,
Two of the most important problems in the laboratory testing of soils concern the determinat
ion
of the compressibility characteristics of a soil in the consolidat ion test and the deter= mination of the shearing strengtho They both attempt to determinedefinite physical properties of a soil that are essential to . any rational attempts to predict settlements of structures and to make stability analyses in a wide variety of practical
problems0 Both types of test are the subject of a large number
of papers dealing with both their theoretical and practical aspectso In the final analysis the validity of the laboratory results of such tests depends upon the accuracy with which
field behaviour agrees with that predicted for the structure or soil ｭ｡ｳｳｾ based upon calculations involving the soil
propertie s as meaaur-e d in the 1 aborat ory tests0 Unfortunat ely
there is still a great lack of field data that may be used to check this s ignifi cant factor 0 Moreover. much that is 'available
indicates that the problem of accurately det ermining such soil properties in the laboratory is much more involveu than the early workers in the field had suspectedo
Two major problems in respect to the consolidation test are the effect of rate of loading of the sample and the significance of the ec-calLed "secondary" compr-es sLorr; No papers submitted make important contributions to a better knowledge concerning these two problemso Howeverp several
the boundary between the three stages of settlement as
it ｯ｣｣ｾｳ in laboratory testso A new theoretical treatment
is presented by Geuze and de Bruyn (111:29)* for the
consolidation process based on an approach from the energy point of view o The question of the effect of preconsolidation on the compressibility of a soil is discussed by Haefeli
ＨｉｾＴＲＩｯ He ｡､ｶｯ｣｡ｴ･ｳｾ as a complement to laboratory
consolidation ｴ･ｳｴｳｾ field tests to determine the compressi-bility of a soil to avoid the effects of disturbance of
the soil during samplingo He also calls attention to a present trend to substitute field tests on the soil in situ for laboratory tests on samples which must be removed from their natural environment with a resultant change in properties due to disturbance. This school of thought would utilize field load bearing ｴ･ｳｴｳｾ penetration tests, measurements of piezometric pressures and so forth rather
than attempt to determine strength and compressibility characteristics in the laboratory0
The problem of the shearing strength of soils, which in the early days of Soil Mechanics seemed perhaps as
simple of determination as for other common materials of
｣ｯｮｳｴｲｵ｣ｴｩｯｮｾ has proven to be most elusive of solutiono
The basic concepts of the nature of shearing strength in soils as well as the factors which govern its value under different types of loading and soil moisture conditions are the most difficult as well as the most controversial of the whole field of Soil Mechanicso It is not surprising therefore to find a large group of contributions concerned with both theoretical concepts and laboratory test
procedures dealing with shearing strengtho Howevera the scope of this review will not permit even a summary of the conclusions of the several intricate theoretical
discussions concerning shearing strengtho We will rather confine our attention to the current laboratory methods of determining shearing strength.
The triaxial compression test equipment has become standard in practically all Soil Mechanics Laboratories
and has to a considerable extent replaced the direct shear test, particularly in research work. Under conditions of test in which no drainage is permitted in a saturated cohesive soil, the unconfiped compression test is a satisfactory substitute for triaxial tests since the
angle of internal friction is zero for these test conditions. Several writers point out that it is seldom that an
unconfined'compression test is truly a test with no lateral pressureo Depending upon the soil ｴｹｰ･ｾ its
density and moisture contenta the sample may be subjected * Figuresin brackets refer to the volume and page number
of the paper referred to in the Proceedings of the Rotterdam Conferenceo
to a lateral pressure greater or less than zerop and moreover it may even vary with a complete change of sign during the testo Its value will depend upon the excess hydrostatic pressure in the water phase of the sampleo
An investigation of "The Angle of Shearing Resistanoe in Cohesive Soils for Tests at Constant Water ContentU 1s
reported
?y
Golder and Skempton (Ig185)o The tests were done with triatsl.a1 equipment and were "quick" tests (as known on this contibent)o While their tentative conclusiohsare based on a test1ng programme of limited extentp they neverthelessare interestingo For fully saturated c1aysp either soft p stiff or remou1ded» the angle of internal friction is zero for the conditions of the ｴ･ｳｾｯＮ For all partially saturated elaysB undisturbed p remoulded,Jr remou1ded and compactedp the angle
of internal friction is greater than zeroo Also for clay
shales and siltstones, saturated or otherwisep and for saturated undisturbed silts the angle of internal friction is greater than
zeroo
Several variations 1n test technique ｷｾｴｨ triaxial compression tests are in use 1n Europeo One such variation in common use in Holland and Belgium is described by de Beer ina paper "Correlation between the Results of Ce11=Test and Compression Tests" (Igl73)o In the "cell test" an overall pressure is applied to a cylindrical test specimen and then the lateral pressure is reduced to the minimum value necessary to maintain equi1ibriumo The test is repeated as many times as desired on the same specimen by either increasing or
decreasing the overall pressure and subsequently releasing the lateral pressureo The.test results reported by de Beer were obtained from nquiCJk" testsD that iS9 permitting no
drainage of the samples0
Among several conclusions reached is one to the effect that if the strength from an unconfined compression test is taken as the load at which the first fissures appearp
then fairly close agreement is secured with the results from the cell testo HoweverD advantages claimed for the cell test
are that more complete information concernipg the shearing resistance can be obtained and that a complete test can be run on the same sampleo The results reported in no instance give an angle of internal friction of zero for the "quiCk" cell testa Thus they are not in accordance with the results of the Golder and Skempton tests nor with those reported on this continent for "quick" triaxial tests on sa tura ted clays0
The cell test results bears a resemblance to those from "conso1idated'=qulck" triaxial tests a s reported on this continento
The direct shear test is still used quite
ｷｩ､･ｬｹｾ particularly in Great Britain. Analogous results may be secured from both direct shear and triaxial tests for most soil types. A saving in time for routine testing is claimed with the direct shear test. It is not
satisfactory for critical density ｳｴｵ､ｩ･ｳｾ but on the other hand critical density values from triaxial tests apparently do not agree with those for natural deposits of the same materials. The direct shear test has some advantages in running "consolidated quick" or "slow" shear tests in that a thinner sample may be used» permitting more rapid
consolidationo However» the direct shear test has the inherent disadvantages that the stress conditions on the sample are not as accurately ｫｮｯｷｮｾ serious stress ｣ｯｮｾ
centrations may ･ｸｩｳｴｾ and deformations cannot be FS
accurately determined as in the triaxial test.
The ele ctro=osmotic drainage of soils Us ｾｨ･
subject of three contributions from Great Britain 9 vhe Netherlands and the United States reporting laboratory
investigations concerning the fundamental principles involved from the three separate countries. Useful design coefficients for various soil types are presented by La Casagrande.
The electro=chemical effects of the process are being given attention in a number of laboratories from the point of view of soil stabilization of fine grained so11s. ｔｨｾ
formation of varved structures in clays incidenta to the electro=osmosis process is of particular ｩｮｴ･ｬﾷｴｈｾｴ
in CBnada due to the wide occurrence of varved clays in Eastern Canada whose peculiar properties are reported in a contribution entitled "Notes on Some Canadian USiltb"" by Legget and Peckover. ＨｉｉｉｾＹＶＩＮ
DISCUSSION
A general discussion followed the presentation of this Section» with particular reference to the triaxial compression test. The apparatus used in this test was generally described by Dean ｈ｡ｲ､ｹｾ and it was noted that a number of different designs have been developed. No standard design has been adopted since the apparatus is generally used for research purposes. The time of
running the test is most important to the results obtained which can be interpreted in different ways9 depending upon the test procedure adopted. Confining pressures used in the tests are chosen so as to obtain conditions most closely approaching those ｲ･ｱｵｩｲ･､ｾ and the principle of the Mohr circle is generally used in such a choice.
100
Mro Kendrick inquired if any investigation had been made of oonditions represented
on
the ｾＱ､･of
theMohr
olreleto the left of the vertical ax1s$ and Dean Hardy said that such conditions are encountered in testing materialsp stones and
｣ｯｮ｣ｲ･ｴ･ｾ where tensile strength is a factoro
On an inquiry from Professor Hurtubise, Dean Hardy expressed his opinion that the triaxial compression rather than the direct shear test is more useful when dealing with a silty soLl.,
Regarding triaxial compression testsi Professor
Morrison noted that the test procedure is not as simple as was first thought and mathematics show how dependent test results are upon test procedureso Different values of the angle of internal friction result from variations in the method of application of vertical and lateral pressureso
In ｧ･ｮ･ｲ｡ｬｾ Professor Morrison thought that the shear
strength of a soil can be obtained from any recognized shearing testo The unconfined compression test is used to obtain
experimental results in Great Britain on London clays which are saturatedo A field report on the condition of samples is most important in evaluating the results of tests to obtain shear strengthsp however9 as is the sensitivity of the soilp
the value of which should be found if too conservative
results are to be avoidedo He considered that a series of
ncorisoLf dated=quicktt tests are generally satisfactory for shear
strength determinationo
Professor Morrison mentioned a paper by Ko Hruban which is of interest in considerations of the determination of shearing strengtho*
This paper points out that the angle of internal friction is not a soil constant but a function of two
parametersp one of which is the cohesion9 taken in a physical
senseo It also mentions that care must be taken to distinguish between this concept of cohesion and the intercept of the
Mohr envelope on the vertical coordinate axis of the Mohr diagramp which is often also called the Ilcoh es i ontto The term
"Coulomb cohesion" is suggested for this value in order to make a distinction between these termso
'"' Ko Hruban "The Flow Limit with Localized Loading in the Half space "; International Association for Bridge and
II.
Referring to the ｈ･ｮｫ･ｹｾｶｯｮ Mises equation for plastic flow, it can be shown, depending on the type of stress system under considerationp that different values of the angle of internal friction can be obtained as a result of tests. For examplep in the triaxial comPression test, if the axial load is sloWly increased with a constant lateral pressure until failure occurs p a different theoretical value of the angle of internal friction will be obtained
as compared with a test in which a constant axial load is applied with the lateral pressure increasing until failure occurs.
120 Sect ion 5
FIELD INVESTIGATIONS
(Section III or Rotterdam Proceedings) by Ro Peterson,
It would seem appropriate to open this Section with ｾ statement or impressions gained at the International Conrer=
ence relative to rield investigations and equipment usedo
My
impression., formed rrom the discussions at the Conference and a visit to the Delrt Laboratory where rield equipment was on
､ｩｳｰｬ｡ｹｾ was that a simple cone penetration device was one
of tbe chier methods used to evaluate roundation conditions in Hollandp where the soils are apparently very soft and looseo
(a) Boring and Sampling
In recent years the art or taking "undisturbed" samples has developed a good dealo This is relt to be a
notable advance as the reliability or laboratory test results and subsequent analyses depend on the quality or the original
samp Le s ,
The chier improvements in soil sampling are2
10 Reduced wall thickness of samplers, indicated by an area ratio of Ｙｾ or ｬｏｾｯ This is the ratio or the tube cross section to the total ar-ea , based on the outer diameter of the bub e ,
20 Allowance or inside clearance at the cutting edge that iSJ the inner diameter at the cutting edge is
somewhat less than the inner diameter of the tube itselro
30 Rapid continuous penetration or the samplero
40 Introduction or piston=type samplers0
A recent development in Sweden ＨｉｾＲＵＵＩ is a core extractor which is designed to recover long continuous
undisturbed cores of sort Boilso In this ｳ｡ｭｰｬ･ｲｾ friction and adhesion between the core and the barrel are eliminated by
the use or thin., rlexible hands or roils which support and conrine the sample0 These foils are attached around the
circUIDrerence or the pistono As the barrel or the sampler is rorced into the so11., the piston remains stationary and the roils are unwound rrom small spools located in the walls or the sampler a short distance behind the cutting edgea
13.
Other developments include a method of carrying out loading tests in the bottom of a drill hole by means of a loading piston operating through the sample barrel
(I:244)o The same loading apparatus is used to measure the resistance to penetration offered by a sample spoon.
Of particular interest is a study of the effect of disturbance of clay samples on the physical test
results (Ig250)o This was done by comparative testing of samples recovered with the old-type samplers having thick walls and with the improved types. The improved type recovered samples which exhibited less disturbance as indicated by sliced sectionso It was found that samples recovered with the improved samplers had a lower
compressibility and a higher unconfined compressive strength than those recovered with the older-type samplers. Rather surprising at first is the fact that the strength determined by the ttconsolida ted-quickll triaxial test is lower for the
samples with least disturbance. It was found that the
modulus of elasticity was extremely sensitive to disturbance, and even the very best samplers caused a reduction in the modulus value as compared with that from large chunk samples.
(b) Measurement of Special Soil Properties
A simple device to determine the relative permeability of peat in situ is described (I:258). This consists
essentially of a standpipe attached to a porous point located in the strata to be testedo The drop in water level in the standpipe is plotted against time for purposes of comparison.
Another new type of field device is the rotating vane9 by means of which the shear strength of clay layers
which are not too hard can be determined in place (I:265). This device consists essentially of a. shaft and a thin
plate fastened vertically to it. After imbedding the plate in the soil» it is rotated about the shaft causing shear failure in the soil. The torque required to turn the plate is measured and the shear strength of the soil so computed. It would seem that this method is quite
economical and accurate in an homogeneous soilo
For preliminary field investigations, sounding methods utilizing a small cone are used extensively in
several European countries. To date, cone sounding devices have not been extensively used on this continent but they are now commanding more interest» particularly for sand foundations. The Dutch sounding device (I:277) consists
140
of a 60 degree cone which is about 1-1/2 inches in diametero It is forced into the foundation and a continuous record of force versus depth is kepto The earlier type of cone did not give accurate results because of side friction on the driving tube behind the coneo The new improved mechanism permits movement between the tube and cone and makes possible the
determination of cone resistance onlyo Where the cone is being used in areas where the succession of strata is not known» a
small diameter tube is provided to recover sampleso While for the most part the results of this test are used in
connection with pile problems, apparently some use is being made of the results for strength determinationso
(c) Measurement of Pore Pressure and Deformations
In recent years the measurement of pore pressures in embankments has assumed great importance as this data is used not only in design studiesj but frequently to warn of
dangerous conditions during constructiono The simplest device consists of a porous point attached to a pipe which is placed in the ground and pore pressure fluctuations are determined by means of a Bourdon gauge0 Other arrangements consist of
cells located at a considerable distance from the measuring device with one or two tubes being used to connect the cell with the measuring deviceo Measurement of the pressure is by one of the following means:
10 Bourdon gaugeo
20 Building up pressure equal and opposite to the pore pressure to maintain a diaphragm at a
predetermined position as indicated by electric
de vd c e s ,
30 Pressure determination by deflection of a
membrane as measured by SR-4 strain gaugeso It has not yet been demonstrated that SR=4 strain gauges will provide accurate long measurementso As for earth pressure ｣･ｬｬｳｾ the WoEoSo type seems
m
be the chief advance in recent years ＨｖﾷｾＶＸＩ u In this cell,which is approximately one inch thick and 12 inches in diameter, the earth pressure exerted on an outer membrane is rendered
uniform by being transmitted through oil to an inner membrane which activates electric strain gaugeso
150 (d) Vibration Research
In this section two papers deal with soil vibration (IIIg214) and the application of the seismic method to foundation exploration (111:218)0 It is felt
that this method is acceptable where preliminary explor-ation is required over a very large areao
(e) Aerial Photography
In recent years more and more use has been made of aerial photographs in connection with civil engineering investigations and soil mechanics studieso This development gained impetus during the war when the method was used for preliminary studies of air bases and other works in unknown regionso Soil conditions can be evaluated approximately by a trained person on the basis of land ｦｯｲｭｾ ､ｲ｡ｩｮ｡ｧ･ｾ
soil ｣ｯｬｯｵｲｾ ･ｲｯｳｩｯｮｾ and ｶ･ｧ･ｴ｡ｴｩｯｮｾ as revealed by the
air photoso This type of study has application in
connection with most types of field exploration, partic-ularly along routes of highwaysp railways and pipe lines and for flying fieldso Based on our experience in Western Canada it has proven particularly useful for locating sand and gravel for construction purposeso One very common land form associated with send and gravel deposits is the Ｂ･ｳｫ･ｲｮｾ which is generally very obvious on air ｰｨｯｴｯｳｾ
appearing as a whitish lineo In the mapping of the north-land and studying permafrost ｣ｯｮ､ｩｴｩｯｮｳｾ air photos have already proven valuable because permafrost is associated with patterns revealed by aerial photoso
DISCUSSION
In the discussion on this ｳｵ｢ｪ･｣ｴｾ the Chairman commented on the "vane" test for determining shear strength of soils in the fieldo He had seen a device similar
to this us ed at the United States Department of Agri culture Experimental Station at ａｵ｢ｵｲｮｾ Alabama, in ＱＹＴＵｾ and was of the opinion that a complicated state of stress was produced when the vane was rotated, possibly resulting in an erroneous value of the angle of internal ｦｲｩ｣ｴｩｯｮｾ
depending on the nature of the rotating effecto Both Major Bekker and the Chairman felt that the test was not trustworthy0
160
Mro Iverson mentioned that cone penetration tests are being carried out by the PoFoRoAo in Bear Pot Shale on the site of their dam on the South Saskatchewan Riverp and ｣ｯｲｲ･ｾｴｩｯｮ
of the field data so obtained is being made with laboratory test resultso "Field measurements of the subsidence of
enbankments are also .bed ng made by means of settlement gauges on the sto Mary Dam project:tt .The Chairman mentioned his own
interest in the cone penetration test which he believed was first developed in Switzerland for the purpose of determining the properties of snowp and subsequently of soilo
Mro Peterson reported the use of a rapid field method for determining the moisture content of soilo It is composed of an electric heating element and a blower which passes hot air through the sample to produce rapid dryingo Results agree well with laboratory determinations of moisture contento
Mro Peterson believed that this blower method is faster and more reliable than the alcohol methodp although involving an
initial expenditure of $140000 for the apparatus0
Dro Radforth reported some of his unusual experiences in attempting to obtain samples of muskego During the summer he has been engaged in investigating the geographical
dis-tribution of organic materials in the Orkneys and Shetland Islandso In trying to obtain samples to determine differences in the properties of these materials at various depths, he encountered great difficulty in operating a core samplerp and
requested suggestions for a boring device which would penetrate muskeg satisfactorilyu Mro Peterson suggested in reply that
the Swedish sampler described in his report might possibly be used for such worko He considered that a sampler of large diameter was essential and a 6-inch core barrelp as used for
Section 6
PROBLEMS OF ROAD AND RUNWAY CONSTRUCT LON (Section VIII of Rotterdam Proceedings)
by Dr. Norman Wo McLeod
In spite of the fact that almost every country has roads and ｡ｩｲｰｯｲｴｳｾ the 39 papers prepared for this Section come from only nine out of the 27 countries contributing to the Proceedings of the Conferenceo
As a general comment on one phase of the
Conference ｰｲｯ｣･､ｵｲ･ｾ it might be mentioned that digests of the papers for each of the twelve sections of the Conference were prepared by a reporter appointed for the purpose
several months before the ｭ･･ｴｩｮｧｾ as a guide to ､ｾｳ｣ｵｳｳｩｯｮ
at the Conference itself. Possibly at the request of the Committee on Organization for the Conference, the reporters for some of the sections also undertook the role of criticso Consequently, these digests sometimes consisted very largely of only the material that had been screened through the
personal prejUdices of the respective reporter, instead of being a resume of the contents of the papers themselveso
In one instance in ｰ｡ｲｴｩ｣ｵｬ｡ｲｾ this approach led to very vigorous repercussionso
Several papers in this Section refer to some of the better known methods of soil classification. There are papers on the stability of slopes for cuts and embankments,
on ､ｲ｡ｩｮ｡ｧ･ｾ and frost actiono Most of the information
contained in these is reasonably familiaro
A paper from France (V:189) discusses a study of the development of washboardp as observed on gravel roads
in the Sahara desertp and investigated experimentally on
a circular track near Pariso Washboard was found to be dependent upon the presence of a layer of loose granular material on a hard base. Washboard does not develop if
the granular material is well bound with a bituminous or
clay binder. On the test ｴｲ｡｣ｫｾ it was found that no washboard developed at speeds below 12 miles per hour. The rate at
which the corrugations formed and the distance between them increased with increasing traffic speedo Stiff springs and high pressure tires retarded the development of washboardo
A paper from the UoS. Corps of Engineers (V:206) deals with problems of the trafficability of soilso In military operations ｰ｡ｲｴｩ｣ｵｬ｡ｲｬｹｾ motor vehicles employed
180
for attack and supply must frequently leave the road and
endeavour to travel over natural groundo This presents serious problems in swampy areas where soils are soft 9 and in territory where there is much loose sando ConsequentlY9 there is need for simple test equipment that will provide adequate information with regard to the ability of various soils in their natural state to carry vehicles with different tractive equipment such as rubber tires9 tracks9 etco Some promising results have been
obtained with cone penetration te sts and with simple shear apparatus for measuring the strength of the soil in placeo
Several papers deal with different phases of the Westergaard method for rigid pavement designo The
Westergaard method still provides the only widely accepted approach to solving the problem of how thick a rigid pavement must be to carry any given wheel loado
The flexible pavement design problem9 that is,
the problem of the thickness of flexible pavement required to carry any given wheel ｬｯ｡､ｾ appears still to be a long way from a generally acceptable solutiono The variety of the approaches to this problem is well illustrated in the considerable number of papers in the Proceedings that deal with ito Each of these various approaches employs its own criteria for design9 and each results in a different thickness requirement for any specified wheel loado Several papers refer to the use of plate bearing
tests for evalua tion and de st gn , A number of papers discuss the California Bearing Ratio method of design advocated by the UoSo Corps of Engineerso At least one method is based upon measuring the shear strength of the subgrade soi19 and another
method upon the results of the triaxial test on subgrade samples. Reference is made to Burmisteras theory of flexible J'avement
design based upon a mathematical analysis of the properties of layered systems i and Boussinesq and the elastic theory are also mentioned as bases for designo
Probably the most striking impression that one obtains from the 39 papers prepared for the Section on road and runway construction is this great diversity of opinion concerning the flexible pavement design problemo Howeveri in
view of the large amount of concentrated study that is being devoted to this problem in a number of countriesi it is possible that some generally acceptable method of design may be developed during the next decadeo
Several interesting types of pavement construction were observed in Europeo Probably the most unique of these
190
near Amsterdamo The subgrade consists of a very soft
sandy clay soilo A portland CBm8nt concrete slab 12 inches thick was placed directly on the subgradeo On top of the concrete there is 14 inches of sand, then 10 inches of crushed ｳｴｯｮ･ｾ and finally an asphaltic concrete surface two inches in thickness, to give a total overall thickness of 38 incheso This design is intended to carry an aeroplane wheel load of ＱＵＰｾｏｏｏ poundso It was adopted in part to protect the portland cement concrete from stresses due to differences in temperature and humidity between the top and bottom of the ｳｬ｡｢ｾ to which it is always exposed on the
surfaceo Also, by having the concrete directly on the
ｳｵ｢ｧｲ｡､･ｾ its beam action would distribute the transmitted
load over a much wider area of subgrade than would a considerably greater thickness of granular materialo
At Orly Airportp the new international passenger
plane terminal for Paris, a section of prestressed concrete about six inches thick is laid over a part of one runwayo
It is 200 feet wide and 1400 feet longe The concrete was precast off the runway into blocks one metre squareo The concrete blocks were placed on two inches of sand underlain by eight inches of compact subgrade (90 per cent modified AoA.SoHoOo density)o Transverse cables were strung the width of the ｲｵｮｷ｡ｹｾ one metre ｡ｰ｡ｲｴｾ in grooves along the sides of the blocks" The cables were stressed by means of
jacks to exert a compressive strength of several hundred pounds per square inch in the concrete, and were locked into place so as to maintain this stresso Through the use of 45 degree diagonal joints across the runwayp and of concrete abutments at each end of the experimental section, both
longitudinal and transverse compressive stresses were obtained from the transverse cableso It was claimed that this prestressed concrete pavement about six inches thick has a much greater load carrying capacity than ordinary concrete 12 inches thick on the same foundationo No cost data could be obtained, but it was the opinion of a number of well informed European engineers with whom the matter was discussed that the unusually high cost of prestressed
concrete, using the construction methods employed for it up to the present p did not make it attractive for pavements for runways or highways in comparison with ordinary concrete at this t Lme,
The writer was greatly interested in the roads and streets of Western Holland, many of which are paved with bricks or stone blockso These bricks or blocks are set on a sand or gravel base, but unlike similar construction in North America they are not grouted with an asphalt or
200
portland cement bindero The void space between the individual stone blocks or bricks is ｦｩｬｬｾ､ with fine sando This type of ｰ｡ｶ･ｭ･ｮｴｾ which is surprisingly stable under traffic, would. therefore seem to be in effect a refinement of the old cobble-stone pavement9 the essential difference being the flat surface
of the bricks or blocks 0
Under many of the roads and streets of Western
Holland there is, at small depth, a peat layer up to about 15
feet in thicknesso This underlying peat compresses under traffic, and any road or street built over it gradually becomes depresseda Every few years therefore, the brick or block pavement and
gravel base must be removed and the road or street brought up to grade with sand, after which the gravel base and block
surface are relaido Occasionally the depth of fill required on these occasions is reported to be as much as three feeto It is because of the necessity for this occasional removal that the bricks or stone blocks used for the pavement are not grouted into place with asphalt or portland cement mortaro The omission of grouting also ｦ｡｣ｩｬｩｴ｡ｴ･ｾ the removal of the block surface when small local depressions must be correctedo
This tendency for many roads and streets to settle makes a permanent asphalt or concrete pavement impractical in certain parts of Western Holland at this timeo For example, a concrete pavement laid between the Hague and Utrecht settled as much as two feet in nine yearso
In Western Europe9 including the British Isles,
problems of road construction appear to be greatly different in general from ours in North Americao Over a period of several hundred years, these countries have developed an arterial road systemp nearly all of which now has an excellent foundation
because of the ｧｲ｡ｶ･ｬｾ crushed stone, and even stone block pavements that have been added over the centurieso Many of these roads are said to have been originally laid out and constructed by the Romans 0 They have been so sturdily built
that most of them are reported to bavefsuffered little or no damage from the heavy traffic of the ｷｾｲＧｹ･｡ｲｳｯ Many of these roads and streets have a stone block surface which, however,
is quite noisy and not too smooth for automobile traffico One of their major road building problems today would seem to consist of developing and constructing an inexpensive smooth riding surface over these ready=made f'oundat Lo n s ,
In North America and in most of the world outside of Europe, a very different set of conditions is usually found, for road construction on a large scale to meet even relatively modest highway engineering requirements is so recent an
21. and designing a suitable pavement for any project is
only one part of the problem. Engineers must be able to work out the most economical design for the entire road
ｳｴｲｵ｣ｴｵｲ･ｾ subgrade9 base course9 and pavement.
The problems of airport construction in Western Europe, on the other hand9 are identical with those of tne
rest of the wor-Ld , for unlike most of their road systems, there is no ready-made foundation waiting to be paved. As in other parts of the ｷｯｲｬ､ｾ a new airport must start from an open field which has usually been previously devoted to agr icul ture c
In the countries of Western Europe there is a
great deal of activity in airport construction at the present
ｴｩｭ･ｾ and there probably will be for the next 10 to 20 years.
In the occupied areas particularly, the bui Ldtng of airports meeting modern requirements was at a standstill during the war and is just being resumed. This need for modern
airports is probably true of every country in Europe, and of most other countries throughout the world for that matter. Even in the British Isles, in spite of the
hundreds of airports built during the war, airport construction is still going on. The heavier postwar aircraft are making new airports with stronger and longer runways necessar,r nearly everywhere.
DISCUSSION
In the discussion on this Section Dean Hardy reported that the British Road Research Laboratory is attempting to develop some cheap surfacing materials for roadways. In England the road problems are somewhat different from those in Canada due to climate as well as to local soil conditions. The ･ｦｦ･ｾｴ of climate is notable. For instance, investigations of frost boils show that frost trouble only occurs on secondary ｲｯ｡､ｳｾ since 14 to 18
inches of subgrade base course materials are used on primary roads and the maximum frost penetration does not
exceed this amount.
Preliminary studies carried out for a highway from London to Manchester included investigation of various compaction methods. In England, compaction is most easily done with rubber-tired equipment because soils are generally saturated and wetter than optimum. Experience has shown the advantage of using rubber-tired equipment and accepting the lower soil strength and density which it gives rather than using sheeps foot rollers and obtaining a doubtful compaction job.
The Chairman noted the valuable contributions of the British Road Research Laboratory to investigations of roads and traffic in tha t countir-y , The Labora tory includes a large Soil Mechanics Departmento One of the interesting problems recently. investigated is to what extent road performance is dependent on the moisture content of the under-Lytng sot L, For this purpose' a simple, means of folloWing changes in the moisture content of
soil under roadways has been developedp consisting of electrodes
enclosed in a plaster of Paris blocko The moisture content of the. soil mass can thus be found at any time without disturbanceo
Section 7
TOUR OF MONTREAL ROAD SITE
At the end of the morning session the delegates were taken on a brief tour of the site of the Montreal Road
Laboratories0 Time was spent at the excavation 'for the new'
building of the Division of Chemistry and in the Aircraft
Structures ｾ｡｢ｯｲ｡ｴｯｲｹ of the Division of Mechanical Engineeringo Lunch 'was ser-ved in the cafeteriao
Section 8
EARTH ｐｒｅｓｓｕｒｅｾ STABILITY AND
ｄｉｓｐｌａｃｾｭｎｔ OF RETAINING STRUCTURES
(Section V of the Rotterdam Proceedings)
23.
by
Messrs. F. Lionel Peckover and William R. Schriever
The contents of this Section come under the following headings: (a) (b) (c) (d) Information on absence. Theoretical considerations;
Earth pressure against rigid vertical walls; Earth pressure against flexible vertical walls,
Earth pressure against underground structures. earth pressure cells is conspicuous by its (a) Theoretical Considerations
Jaky of Hungary (I :'103) deals with grain pressures developed in ｳｩｬｯｳｾ reaching a solution which he considers more compatible with the laws of statics than the.classical
theory of Jansseno He assumes that the pressure varies with diameter of silo as well as with depth and gives a table showing the angle of internal friction and wall friction obtained with different grainso
(b) Earth Pressure against Rigid Vertical Walls
This sub=section contains papers with data on retaining wall tests i design practice and construction,
and failures.
A paper from Stockholm (II:71)J describes half scale tests made to find the pressure exerted by a backfill of gravel, the usual backfill material in this region.
These tests were made to find whether specifications
calling for design using earth pressure at rest were more valid than those calling for active earth ｰｲ･ｳｳｵｲ･ｾ taking friction into account.
Tests on a reinforced concrete walli using
crushed stone with an angle of internal friction of 40 degrees, gave results conforming well with the Coulomb value of pressurei both with and without surcharge. The
pressure was found to decrease about five per cent over two months and the maximum deflection of wall necessary to develop this active earth pressure was less than one millimeter. It was found that about 60 per cent of the
240
increase in pressure due to surcharge remained after it was
removed and there was li ttle increase in pressure when the .surcharge was replacedo In all tests the ratio of horizontal to hydrostatic' pressure was found to be approximately ＰＰＲＲｾ and in all tests an insignificant yielding was sufficient to reduce the pressure from that at rest to active p r-es sur-e ,
Dealing with design practice, Mro Paduart of Belgium (111:287) defines the stability against overturning of retaining wallso The factor of safety usually employed in this determina-tion is the ratio of the stabilizing moment to the overturning
ｭｯｭ･ｮｴｾ but by means of examples he points out that such a
factor of safety is illogical and ambiguous since it is equal to the quotient of two quanti ties, constituents of which can be changed from one to the other with a mere change of signo
ｔｨ･ｲ･ｦｯｲ･ｾ it is different from factors of safety commonly used
in tha t i t s numerical value do es no t say how far a wall is from
overturning. He suggests the use of the term ltreserve of stability" instead of factor of ｳ｡ｦ･ｴｹｾ defined as the algebraic sum of
the stabilizing and overturning momentso Assuming normal design conditions, this reserve of stability is inadequate for ensuring stabilityo HoweverJ assuming critical conditions, it gives a
positive or negative value, which tells whether the wall is safe or not under these conditions. Theauthor ｩｬｬｵｾｴｲ｡ｴ･ｳ the use of this ｦ｡｣ｴｯｲｾ which provides seourity in the form of allowances for most unfavourable conditions rather than in the form of
graphical procedureso
Mro Little of England (111:284) deals with the use of Soil Mechanics in the design of large dry dockso These
structures are usually designed to floa t in sa tura ted gro und , Pressure on the side walls is taken to be fluid pressure plus an additional pressure due to the ｳｯｩｬｾ and values for the latter give a comparatively small difference in pressure between good and bad soilso Pressure distribution is commonly assumed to ｾ･ hydrostatic but more research is needed to determine the actual distribution ｡ｮｾ point of applicationo
Mro Epstein of UoSoAo (111:291) deals With the reduction of lateral pressure of cohesive soils against sheet piling by
the use of sand dikesu Such a reduction in pressure is due mainly to the shearing strength of the sand and to its
transmission of friction forces to the sheet pilingo Test results show that active pressures against piling from a backfill and surcharge may be reduced as much as 70 per cent by means of sand dikes. A rectangular dike uses least material but is expensive to place and only reaches full effectiveness when its thickness is 007 of its heighto A triangular shape of dike is therefore recommendeqp ranking second in material
250
A paper from the United States (III:296) reports data on retaining wall failures and movements, collected by means of a questionnaireo In all reported cases, the only common factor is clay, present either in the foundation or the backfill and usually in botho They recommend that much more attention be given to foundation conditions and
to possible changes that may take place in the backfill over a period of timeo
(c) Earth Pressure against Flexible Vertical Walls
Among the papers of this ｳｵ｢ｾｳ･｣ｴｩｯｮ certainly the most important and also the most controversial are those dealing with anchored bulkheads and other flexible retaining ｷ｡ＱＱｳｾ Although anchored bulkheads serve, in
ｰｲｩｮ｣ｩｰＱ･ｾ the same purpose as retaining ｷ｡ＱＱｳｾ they take
up the active earth pressure partly by means of anchor rods and partly by the passive resistance of soil at the toe of the wallo The weight of the ｢ｵＱｫｨ･｡､ｾ usually
steel sheet piling, is sma110 Another important difference from retaining walls is that bulkheads are f1exib1eo The upper and lower ends are practically fixed, but the middle part yields horizontally by bendingi which is a type of
yield entirely different from that occurring with con-ventional retaining walls and in braced cutso
For a retaining wal19 which may tilt about its
base, the classical hydrostatic distribution of pressure of sand on the wall is usually correct. For braced cuts, where the yield is smallest at the top and largest at the bottomi the lateral pressure distribution is roughly
parabolic. In bu1kheads9 it is usually agreed that the
distribution of pressure deviates from the hydrostatic, while the total pressure remains practically unchangedo The deviation in distribution9 due to the type of yield,
consists in increases over hydrostatic pressure at the
anchor point and at the bottom9 and a corresponding decrease
in the middle portiono Terzaghi, therefore, recommends allowing for an increase in anchor pull of 20 per cent, while reducing the bending moment to a value of probably not over half that computed on the basis of hydrostatic pressure distribution.
One of the most important problems in bulkhead design is the depth to which sheet piles have to be driven. Depending on the opinion of the designer and on the depth of penetration chosen, bulkheads are usually regarded as having either a "free earth support" or a "fixed earth
260
Two papers present some of' the results of' an extensive programme of' earth pressure tests done at the Princeton
University (11;819 ｉｉｉｾＳＰＸＩＹ with scales of' 1:5 and ＱＺＸｾ on
f'lexible bulkheads with ｣ｬ｡ｹｾ sand, and sand=clay mixtureso The clays were placed in a f'luid condition and measurements were taken though all stages of' consolidation9 with some unusual
conclusions0 Af'ter reaching a s ta te of' 11cons olida ted equilibrium"
in clay>; the ratio of' hor-Lz ont.a.L to vertical pressure was f'ound to be approximately 005 f'or all soils testedo Under normal
f'ield conditions the active earth pressure of' naturally consoli-dated clays seems to be approximately the same as the pressure at resto In submerged sand backf'ills9 arching was not f'ound to
decrease bending moments to the extent sometimffiassumed9 since
it cannot develop during normal backf'illing operationso In
addition it is proposed that all arching has an unstable character and should not be relied upon in the design of' f'lexible bulkheadso
Among the other ｰ｡ｰ･ｲｳｾ Browzin of' France ＨｉｉｉｾＳＰＲＩ
and Davidenkof'f' of' Germany (V:122) arrive at the same conclusion tMt the method of' ttf'ree earth suppor-t" is pref'erable to that of' IIf'ixed earth suppor-t." 0 A pap er by Pa CkSM w of' England (II :86 )
deals with earth pressure on f'lexible walls in general and
contributes some valuable suggestions f'or f'uture research Which are partially f'ulf'illed by the Princeton testso A Dutch paper
(IIg91) shows a method of' computation f'or a quay wall with a relieving platf'orm as proposed by the late Prof'essor Buismano
Two papers deal wi th pressures on trench and shaf'f
timberingo An English paper by Golder (11:76) gives measurements of' pressure against tpe timbering of' a trench in clay and an
American paper by Peck and Berman (111:300) gives those against a deep shaf't in plastic clayo Both show that the pressure
distribution is not triangular as according to the classical theory but is greatest approximately at midheighto In the shaf't the maximum pressure was only about 46 per cent of' that generally assumed f'or open cuts9 as a large part of' the lateral pressure
was transf'erred to the soil beneatho
An American paper ＨｖｾＱＰＷＩ presents a report on f'ield and laboratory tests on the stability of' posts against lateral loadso It was f'ound that the point of' rotation f'or the case of' overturning is about two=thirds of' the buried length below the ground aur-f'ac e ,
(d)
Earth Pressure against Underground structures The Amsterdam Department of Public Workspresent a paper (III:317) which analyzes the loads applied to underground conduits and concludes that the manner of support and the method of installation have a great
influence on the loads which resulto
A paper by Messrso RoBo Peck and ｏｯｾ Peck of UoSoAo (II:95) reports the results of observations made of the deformation of large flexible steel culverts
installed in railway embankments of varying heightso Such culverts deform sufficiently to develop pressures practically equal in all directions around their circumference and
hence only sufficient strength is required to withstand
the ring stresses developed. This lack of inherent strength, however, makes it essential that backfilling operations be carefully supervised and controlled$ and this paper gives the recommended backfilling procedureo In genera19 it
is found that these ｳｴｲｵ｣ｴｵｲ･ｳｾ if properly installed, have less initial cost and less maintenance expense than rigid culverts of the same sizeo
DISCUSSION
In the discussion Professor Morrison pointed out that the swelling pressures exerted by cohesive soils behind retaining walls was not mentioned at all in this Sectiono All the papers dealt with forces produced by the action of gravity alone$ which are relatively determinateo Much more difficult to deal with were pressures caused by the
expansion of soils due to an increase in moisture contento He mentioned an interesting case of a retaining wall failure due to this phenomenon caused by the watering of a garden adjacent to the wallo He emphasized that such failures should always be investigated and recorded, since it was only by such field observations that lessons could be learned to assist in proper designo
280 Section 9
PILE FOUNDATIONS AND PILE LOADING TESTS (Section VII of Rotterdam Proceedings).
by DoG. Watt
Of the 30 papers in this ｓ･｣ｴｩｯｮｾ 23 deal with the settlement and bearing capacity of pileso .The most important of these are summarized below under headings corresponding to the three methods available for determining the bearing
capacity of pLl.es , namely dynamic f'o rmu La e , static load tests, and theoretical solutions based on soil pr-op er-t.Le s , The
remaining papers are treated under the headings of. pile design and horizontal pressures on pile foundations 0
(a) Dynamic Pile Driving Formulae
In his general r-eport , Kerisel stated that the
question of the value of dynamic pile driving formulae is one of the most hackneyed in the science of Soil Mechanicso Four of the contributors to this section have independently arrived at the conclusion that pile driving formulae are unreliable0
From a purely mechanical viewpoint it is impossible to
estimate or measure accurately the energy loss on impact on which the validity of these formulae dep ends , There is also the problem of correlating dynamic resistance, which is the quantity measurable on drivingJ) with static resistance of the pile, ioeo its bearing capacityo It is generally agreed that dynamic formulae should never be used as the sole means of establishing the bearing capacity of pileso They can
only be used as a rough indicator of uniform bearing capacity applicable to each pile on a job , provided the result is
checked initially against bearing values established from static load testso
Planterna of Holland (IV:127) records pore pres sure measurements in a sand stratum during pile driving0 He found
that the positive pore pressure increased in the zone surrounding the pile and the time required for it to return to equilibrium was a function of the fineness and the silt content of the sand ,
Huizinga of Holland (11:185) suggests that the observed discrepancy between dynamic and static resistance of piles in sand layers may be associated with the phenomena of critical densityo Loose saturated sand and dense sand,
29. when subjected to shearing deformations during driving, tend to become more and less dense respectively resulting in positive and negative pore pressures and corresponding low and high driving resistances as compared with those encountered when pore pressures are normalo In actual practice one could expect these effects in any degree depending on the dimensions of the pile, pile spacing, speed of driving and the density and permeability of the soilo The author concludes that pile driving formulae based on a given penetration per blow can not provide a measure of the bearing capacity of piles driven into
sand s tra ta c
Feagin of UoS.A o (IV:98) reports on the driving and testing of a large number of timber and concrete
piles in deep deposits of sando The test loads required to produce a settlement of ｯｮ･ｾｱｵ｡ｲｴ･ｲ inch in a single pile exceeded the bearing value indicated by the
Engineering News Formula0 Settlement and lateral movement
of structures founded on a large number of piles were somewhat greater than those observed on individual piles or small pile clusterso
A paper from Denmark (IV:I07) describes the foundations for a bridge founded on piles driven into a fine alluvial sando Tests on nine piles indicated that the Eytelwein formula gave the most applicable resultso The Engineering News Formula gave values 40 to 60 per cent too IOWa
Tschebotarloff and Palmer of UoSoAo (II:195) review model tests on piles performed elsewhere and compare them with similar tests made at Princeton Universityo On their models they utilized electrical
resistance strain gauges (SR-4) to ascertain the proportion of the total load carried by the pile point, by skin
friction and the pile footingo In these tests the
Engineering News Formula and the modified Engineering News Formula gave too low values for dry sand and too high
values for plastic clayso
Housel and Burkey of UoS.A. (V:146), in a paper on the driving characteristics of point bearing piles in soft clay, present valuable information on soil conditions in the Detroit (and Windsor) areaso The report includes boring logs, complete with test data and driving records,
on different types of tubular steel cased cast-in-place piles driven thrOUgh some 90 feet of soft and medium clay to a "hardpan" layer over rock0 Unconfined compression
300
tests made before and after driving are used as an ·index of disturbanceo Soft clay was completely remoulded at three
inches from the pile but was not significantly affected at 205 ｦ･･ｴｾ In medium clay no significant loss in strength was
observed regardless of the distance from ｴｾ pile; in fact the results show an increase in strength after driving whlch is not explained0
Bendel of Switzerland (IV:129) reports on the use
of a ｰ･ｲ｣ｵｳｳｩｯｮｾｴｹｰ･ sounding needle to detect the extent and
degree of disturbance when a 20-inch diameter pile was driven through a peaty loam soil overlying a clean sandy gravelo No disturbance was noted at four pile diameterso At 102 pile diameters the penetration resistance of the soil was found to have decreased while that of the sandy gravel had increasedo
Dro-Terzaghi in the general discussion amplified the remarks on disturbance by reporting on recent pile driving tests carried out at AbbotUs Inch near Glasgow where the disturbance of the clay produced by driving was shown to be negligibleo Although the structure of the clay was destroyed
on ､ｲｩｶｩｮｧｾ it soon 'recovered its initial strengtho
(b) Pile Loading Tests and Deep-Sounding Penetrometers
The deep=sounding cone penetrometer for determining the bearing capacity of soils at depth is Widely used in the Low Countries 0 For the most part the soil profile in these
areas is quite uniform9 consisting of soft clays, sometimes
containing thin layers of ｾ｡ｮ､Ｌ to a depth of about 50 feet where a thick sand stratum of varying density is found. To avoid settlement the light structures in the cities are founded on piles resting on the upper thin layers of sand
while the heavier structures are all founded on piles extending to the deep sand stratumo The main use of the deep-sounding cone is to locate the exact depth of the sand strata and to determine their safe bearing capacityo
A simple form of the Dutch cone penetrometer was described in the Proceedings of the First International
Soil Mechanics Conference in 19369 1:7 and 1:1810 Since then
it ｨ｡ｳ｢･ｾｮ redesigned to incorporate many refinements and
is now commercially available from NoVa Goudsche Machinefabriek, Gouda, Netherlands, in three capacities: 10 kilograms per
square centimeter for shallow depths-operated by one workman; 50 kilograms per square centtmeter and 10=ton mechanically operated models for deep soundingso The apparatus consists
which passes a rod terminating in a 60-degree cone with a base area of 10 square centimeterso With the shoulder of the cone seated on the ｴｵ｢･ｾ the latter is pushed into the ground and the resistance to penetration continuously measuredo At intervals the driving is stopped and the cone
is pushed ahead of the tube by means of the central rodo In this manner the resistance to penetration can be measured at any depthp free from the effects of skin frictiono An
estimate of the total skin friction to any depth can be obtained by subtracting ｴｨｾ point resistance from the total pressure required to advance the tube and cone togethero
Plantema of Holland ＨｉｖｾＱＱＲＩ shows that the penetra-tion resistance as determined by the deep-sounding device, expressed in unit load on the cone base area, can be used to determine the ultimate point bearing capacity of a pileo He compares the results of a cone-sounding record in a thick
sand stratum with the ultimate point resistance of a concrete pile loaded to failure at different elevations While the
skin friction was eliminated0 It was pointed out in the
discussion that this method of predicting settlement would not be generally applicable since for the same point loading per unit of area the settlement would be a function of the diametero
Franx of Holland (IV:118) comments on the bearing capacity of piles as found from deep soundings, loading tests and pile driving formulaeo From such comparisons he concludes that pile driving formulae are of little value, the penetration per blow being only an indication of bearing
capacity for those who have local experience in pile driving, pile loading and sounding testso The author presents some interesting data on the maximum toe resistance to which different types and sizes of piles are driven in Holland to avoid structural injuryo
Huizinga of Holland (II:185) mentions that some 5000 deep soundings have been made with the Dutch cone device in that countryo He claims that the method offers some
advantages over test borings in that it is more rapid and
less ･ｸｰ･ｮｳｩｶ･ｾ and serves a useful purpose in the strategic
location of ｢ｯｲｩｮｧｾ He states that pile driving formulae are unreliable and should never be applied as the sole means of determining the safe bearing capacityo However, to
assess the relative value of the resistance of the soil with depth at each pile location, he suggests that the average penetration per blow should always be recordedo There does not appear to be any other economical method of obtaining
