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Journal of the National Buildings Organization, 6, 1, pp. 106-119, 1961-09-01
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Three buildings on floating foundations in Ottawa, Canada
Legget, R. F.; Burn, K. N.; Bozozuk, M.
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S e r
TH1
N21r2
no.
136
C A N A D A
DIVISION O F BUILDING RESEARCH
THREE BUILDINGS ON
"FLOATING
FOUNDATIONS"
IN OTTAWA, CANADA
BY
R.
F. LEGGET. K. N. BURN AND M.
BOZOZUKREPRINTED FROM
J O U R N A L O F T H E N A T I O N A L B U I L D I N G S O R G A N I Z A T I O N V O L . VI, N O . 1, J A N U A R Y 1961, P.106
-
119RESEARCH P A P E R N O . 136 O F T H E
DIVISION OF BUILDING RESEARCH
.'. r " r " ' g 7 , ' '
U a
dBAJL PRICE 2 5 C E N T S OTTAWA SEPTEMBER 1961 N R C 6516T h i s publication i s being distributed by the Division of Building R e s e a r c h of the National R e s e a r c h Council. It should not be reproduced in whole o r in p a r t , without p e r m i s - sion of the original publisher. The Division would be glad to be of a s s i s t a n c e in obtaining such p e r m i s s i o n .
Publications of the Division of Building R e s e a r c h m a y be obtained by mailing the appropriate r e m i t t a n c e , ( a Bank, E x p r e s s , o r P o s t Office M ~ n e y O r d e r o r a cheque m a d e pay- able at p a r in Ottawa, to the Receiver G e n e r a l of Cariada, c r e d i t National R e s e a r c h Council) to the National R e s e a r c h Council, Ottawa. Stamps a r e not acceptable.
A
coupon s y s t e m has been introduced to make pay- m e n t s for publications relatively simple. Coupons a r e avail- able in denominations of 5, 2 5 and 50 c e n t s , and m a y be ob- tained by making a remittance a s indicated above. T h e s e coupons m a y be used for the p u r c h a s e of all Natiunal R e s e a r c h Council publications including specifications of the Canadian Government Specifications Board.Three
Buildings on "Floating Foundations9' in
Ottawa,
Canada
-- -- - -- - - - -- -- - -- - - - . .- --- - -- -- - - --- - - -
BY R.F. I ~ E G G E T * , K . N . BURN** AND M . R O Z ~ Z U I C * *
Synopsis
Ottawa is situated in a region of sensitive marine clay which varies in depth from a few feet to more than one hundred feet. Due to the structure of the clay, it retains a high water content in its natural state and is thercfore very compressible. Buildings with st1.i~ footings have been known to settle more than one foot.
Until recently, the common foundation consisted of strip footings for small structures, and piles driven to bedrock for the larger buildings. This paper describes the perfor- mance of another type of foundation for large buildings; the mat foundation in wl~ich tl1e building is founded on a reinforced concrete monolithic slab, placed at such a depth that the net foundation pressures are very small.
Settlement observations on several apartment buildings in Ottawa with mat foundations have been carried out during the last ten years. The results are quoted and the performance of this type of foundation is discussed.
NE of the most important contributions made to civil engineering design as a result of studies in Soil Mechanics has been an expla- nation of the inter-relation of the shear strength and the compressibility of fine grained soils in determining their safe bearing capacity. The state of stress created in a soil by the loads transmitted to it by a foundation structure is
weak comprcssible soils by excavating over their sites, then replacing the weight of the soil so removed by the weight of the structure, at least in part, with consequent reduction of both stress in and settlement of the soils as compared with what would have been the case had the building been founded o n the surface of the ground.
now well understood and can be determined
with reasonable accuracy. The picture of Sinlple and sound as is this type of founda- "foundation action" that this advance has tion design, it does not yet appear to be as made generally available has led to the proper widely used as it could be. More conventional questioning of some conventional approaches practices, even though often more costly, are such as the indiscriminate use of bearing piles. still used all too often, probably because de- It has also redirected attention to the old but signers are so accusto~ned to them, possibly sound device of "floating" buildings upon because nobody is interested in "selling" this
- - - - - -- -- - . - - --
*Director, Division of Building Research, National Research Council of Canada, Ottawa, Canada. **Research Officer, Soil Mechanics Section; Division o f Building Research, National Research Council,
alternative r ~ ~ o t h o d , possibly also bccanse there are not readily available many records of the successfi~l performance of this type of foundation, certainly for medit~rnsized build- ings such as make up the bulk of modcr.n urban development. This paper has been prepared in order to provide a record of the foundations of three modern apartment build- ings in the city o f Ottawa. the national capital of Canada.
For the benefit of Indian readers, it may be noted that since almost the entire area of Canada has been glaciated, foundation condi- tions throughout the country are generally good. I n inany areas, bedrock is close to the surface and so can be used directly for the support of structures. Glacial till is widely distributed and provides good bearing for foundations. Glacial action, however. has also provided widespread clay deposits that d o present problems to the civil engineer. Generally these are fresh water deposits of varying sensitivity. laid down in the vast lakes that covered much of Canada in glacial times. I n some coastal regions, glacial marine clays constitute the main soil deposit, with properties just as critical as are displayed by the similar clays encountered in southern Norway and Sweden. Accordingly, throughout Canada there are areas where foundation problems 711leers may be serious and in which civil en&' have carried out special soil investigations (Legget, 1851),
O n the Pacific coast, the few level areas available for building at the base of the Coast Range of mountains are underlain by alluvial deposits o r by marine glacial clays (Hardy and Ripley, 1954)- I11 the area of the Western
plains, over-consolidated shales are encountered that are troublesonle (Hardy, 1057). In the area once occupied by Lake Agassiz, including the city of Winnipeg, both swelling and shrink- ing distinguish the local galcial clay, the limited bearing capacity of wl~ich was demons-
2
tratctl by the failure of Lllc Transcona Elevator (Baracos, 1957). I n the valleys of thc Ottawa and St. Lawrence Rivers, including the cities of Ottawa and Montreal, an unsusually sen~itivc marine clay, known locally as Leda clay because of the presence i n it of shells of Lcrlrr
giaci(rlis, has been the cause of some serious landslides and quite serious building settle- ments (Eden and Crawford, 1957). The build- ings to be described are all founded on this qi~estionable but widely distributed material.
In I940 the Division of Building Research of the National Research Council of Canada initiated a n investigation of the settlements of large buildings "floated" on this trouble- some clay in the city of Ottawa. Three similar buildings in the centre of the city, located within twelve city blocks (two-thirds of a mile) of each other, were selected for study. Each was suitably instrumented to enable total and difyerential settlen~ents to be recorded with time. F o r convenience they are referred t o in the Faper as Buildings A , B, a n d C.
( I ) Site Corzditiotzs (2nd 80il Properties
T h e foundation soil (Eeda clay) was de- posited in the marine environment of the Champlain Sea which existed in the Ottawa- St. Lawrence River Valleys a t the d o s e of the lase glaciation period (Fig. 1). Recent studies (Gadd 1957, 1960 and Terasmae, 1!)59) have shown that this sea existed in late glacial time and that it was affected by inflow of fresh water which created brackish water conditions in places. invariably affecting the deposition of the clays in it. These clays were then exposed by the subsequent uplift which occurred after the glaciers had disappeared. They occur up the St. Lawrence River Valley nearly to Kingston; up the Ottawa River Valley as far as Penibroke; and in the Lake St. J o h n region. The deposits vary in thickness from a few feet t o about 200ft (61 m.) and a r e found a t elevations up to 000 ft (183 m.) a b o v e present
sca Icvcl. T l ~ c cnginccring propc~.tics of the wit11 n licltl vanc instrument. I t mas f o ~ ~ r i d clays i n the Ottawa area have been discussctl that t l ~ c ~inconsolidatctl ~intlrainctl triaxiol by Eden and Crawford (l!)57). test rcsults and thc undisturbed field vane
strengths agreed generally for tile top and bot- At thc three selected site; th? Leda clays
ovcrlie thc dollingwood limestone, a P;!!nezoic fo1.11in~ion (Wilson 1943) which s'opes to tlie south. This bedrock is encountered at a depth of 50 ft (15111.) at site "A", and 104 ft (32 m.) at site "C". Except for the variable thick- ness of the clay deposit in this area, the soil profiles are simil2r at the three sites. A soil boring and sanlpling program at Metcalfe and Frank Streets, midway between buildings A and C and thre: blocks south of B, gave tlie soil profile as shown in Fig. 2. A 6-ft surface mantle of fine sand overlies 4 ft of desiccated brown Leda clay, and beneath this 7 ft of fissured brittle grey Leda clay. The material beneath is very soft and sensitive, becoming 'siltier with- depth. Shells were encountered at'40 ft ( 1 2 m . ) , and at depth of 50 ft (15 m.) a pronounced black mottling due to anaerobic bacteria, a sulphate reducing agent (Crawford 1060) appeared in the grey clay. Glacial till: composed of sand, silt and stones was found at 69 ft (21 m.) extending to 91 ft (25 m.) the depth to bedrock.
The classificatioll tests showed a much greater plasticity in the clay above 30 ft (9 m.) than in that below, except for one layer at a depth of G5 ft (20 m.). This is in accordance with the grain size results which show that the material becomes siltier with d2pth. The natural moisture contents were consistcntly higher than the liquid limits. The resultant values for the liquidity index were all greater than unity indicating the high sensitivity of the material.
Shear strength of the soil was measured in tlie laboratory by unconfined and triaxial con~pression tests. Undisturbed and remoulded strengths were nieasured i n situ
tom clay zones. There wcre insuficicnt vanc tests in the niiddle of the profile to make a good comparison in this region. Only the highest unconfined test resi~lts agreed with tlie triaxial arid vane strengths. The remoulded strengths varied from 1 per cent to 15 per ccrit of the undisturbed strengths. indicating a range of sensitivity froni 100 to 7 rrsp'ecticc~~. The undisturbed shear strengths varied from O.:$
TSF* (0.3 kglcm2) to greater than 1 TSF
( I kg/cm2) with the most probablc value being 0.5 T S F (0.5 kg/cm2) for the soil profile. The modulus of elasticity for the soil was taken as the initial tangent modulus of the stress-strain curves from the triaxial tests, giving val~ies from 350 T S F to 1500 TSF (360 kg/cn12 to 1500 kg/cm2).
The consolidation characteristics of the clay were measured on selected samples in the laboratory. A typical pressure-void ratio curve for the Leda clay is shown in Fig. 3 . Characteristic of these clays is a high initial void ratio (about 2) and a high compression
index (about 2). Minimum probable, and maxi~num preconsolidation pressures plotted against depth i l l Fig. 2 show that the soil at
this site is ocer consolidated by about 1.6TSF (1 .G kg/cm2).
Each of the three buildings is a multi-story apart~nent block constructed as a reinforccd concrete frame, with an exterior finish of brick veneer (Figs. 4, i, and 6). The thrce buildings difrer oldy in the details of construction such as spacing of columns, tl~ickncss of floor; and the location and typc of construction of partition walls.
::< A11 a ~ b r eviatiorl for s h o r t tons
PRECONSOLIDATIOtI LOAD
PL.- PLASTIC LIMIT
-
% L.I. -LIQUIDITY INDEXL.Lr LIQUID LIMIT
-
% PROBABLE Ei- INITIAL TANGENT0 HIGHEST UNCONFINED TEST VALUES MINIMUM MAXIMUM
-
TYPICAL WATER CONTENT-
% + UNDISTURBED FIELO VANE TESTSDEPTH TO BEDROCK
-
91 FEETBORING LOG SHOWING TEST RESULTS AT T H E lMTERSECTlON OF METCALFE AND FRANK S T R E E T S FIGURE 2
2.1 2 . 0 1.9 1 . 8 Pn (mati) 2-46 Kg
/
em2 Pn ( p r o b ) = 2 * 3 8 #g/
@m2 1.5 Bn(min) =2.1 5 ~g/
crnCOMPRESSION INDEX (Ce) = 1.88
X- INITIAL EFFECTIVE STRESS IN SlTU 9.4 A- S - FINAL CALCULATED STRESS FINAL CALCULATED STRESS
@
@ 8 AC-
FINAL CALCULATED STRESS @G
1.3
2 . 0 5.0 10.0
PRESSURE
-
VOID
RATIO CHARACTERISTICS
OF
LEDA CLAY
FIGURE
3
Pig. 4. Building "A" at M~lcalfe rind Fiy 6. Building "C" at Argyle Street and
Lisgar Streets. National Capital Commission
-
Fig. 5 . Building "B" at Metcalfe and Mac.l;aren streets.
Each building and its live load is carried t o the soil through a reinforced concrete mat which extends about four feet beyond the peri- meter wall of the structure. Although the three buildings are some distance apart, the absolute elevations at which their foundation mats were established fall within a range of less than 10 ft (3 m.).
Driveway.
Building A is eight stories high (80 ft., 2 4 m.)
rectangular in plan with a n area of 7,300 sq ft (680 sq m.). It rests on a 27 in. (69 cm) thick mat at 12 ft ( 4 m.) below ground level, creating a total average pressure on the soil of 1.06 T S F (1.06 kg/cm2), or a net pressure increase of 0.59 TSF (0.59 kg/cm2) at founda- tion level. The excavation was made in September 1950 and the building was ready for occupancy in October 1951.
Building B is similar to building A, being rectangular in plan but with an area of 7,500 sq ft (695 sq m.). It comprises seven stories of apartments with two penthouses. Together with an 18 in. (46 cm) thick reinforced concrete mat and 19 in. (48 cm) of compacted earth fill sandwiched between this and the basement floor above, the structure places a total average pressure of 1.20 TSF (1.20 kg/cm2) on the subsoil at a depth of 12 ft (4m). The net in- crease in vertical stress is 0.73 TSF (0.73 kg/cm2) the highest for the three buildings. Two full years were required to construct this apartment block which was completed in July 1949.
Uuildit~g C is considerably larpcr in atsea than the othcr two, having an area of 15,!)00 sq ft (1,750 sq m.). It consists of eight stories of apartments surmounted by a fairly large penthouse. It was erected on a 36 in. (Olcm.) concrete Inat roughly triangular in shape, producing a total average pressure a t 10 ft
( 3 m.) below grade of 0.97 TSF (0.97 kg/em2). The net increase in vertical stress is 0.54 TSF (0.64 kg/cm2). This is the newest of the three buildings, construction having been started in September 1066 and completed the follow- ing June.
( 4 ) Jnstrum.enlaldon nnd S ~ ~ r v e y s
Differential settlements of the colun~ns at basenlent level in buildings A and B were determined with the aid of a water tube level which was described in detail by Peckover
(1052). The apparatus is accurate and rela- tively simple to use. It has the advantage of making it possible to establish, by means of two simultaneous readings, t!le difference in elevation between two stations separated by a maze of partition walls. Such conditions existed in the basenients of both of these buildings. They were partitioned into a number of roonis of various sizes, making it inipossible to use a precise engineer's level. No great difficulties were encountered while using the water tube instrument; i t is considered that the differential scttlenients so nieasured are accurate to within f 0.02 in. (0.06 cm).
About '70,per cent of the survey stations in the basement of building C were located in a large parking space, so that it was possible to use a precise engineer's level to determine differential movement between the column pedestals, which remained a few inches above the finished slab. It was necessary to carry levels into the north-east corner of the basement where partitions existed between locker and service rooms, but this presented no great difficulty. As in the other buildings, some
stations were ~llatlc inaccessible because of minor construction, such as locker rooms or cupboards. Because the level circuits were short and the errors of closure consequently very small, an accuracy of f 0.02 in. (0.05 cm)
i q believed to have been achieved.
Total settlcments were measured by ~tsing a precise engineer's level to determine the difference in elevation between two permanent bench marks and a plug on the outside of a
column in each building, instiuniented as a station for surveys of differential settlement. The accuracies of these exterior surveys de- pended primarily on the distance from the reference point to the buildings. The first of the bench marks located across the street from building A, was 1.000 ft (305 m.) from building B and 3,400 ft (1OiCO m.) from building C. Shortly after the first survey on building C, a second bench Inark was established in a more central position. The estinlated errors of these surveys are &0.005 in. (0.013 ~111)
for buildinp A , f 0.02 in. (0.05 cm) for build- ing B, and f 0.05 in. (0.13 cm) for building C.
Co~ltours of equal settlement, as determined for all three buildings in 1959, are shown in Fig. 7. Time-settlement curves for the points of maximum total settlements of each buildil~g are shown in Fig. 8. A scale showing elapsed time was chosen to facilitat: con~parison of the shape of these curves which, with the possible exception of that for building C, indicate the present rate of settlement to be very small.
It was not possible to measure rebound during excavation but it may be assumed that it would be very nearly equal for the three buildings since the reduction in stresses at foundation level varied by only 0.06 TSF (0.05 kg/cln2). Of more significance would be the different amounts of settle!nent that might have occurred i n the time that elapsed bctwcen maximum rebound and the date of the intial surveys. These would depend upon the relative
TlME , YEARS - I 0 I 0 I 2 I 3 I 4 I 5 I 6 I 7 I 8 I 9 I 10 I U)
-
-
r
-
-
I- z 0 . 4-
-
W A J I- -CONSTRUCTION PERIOD B o- I- $ 0 6 -FOLLOWING EXCAVATION.-
-
z
-
-
1.0 I I 1 i t i I I i I I 1MAXIMUM SETTLEMENT VS. TlME FOR THREE APARTMENT BUILDINGS WITH CONCRETE MAT FOUNDATIOPJS ON LEDA CLAY
FIGURE 8
Cl-C? 1, p=qB -
cated in Fig. 8, building B was complete and E ready for occupancy before the reference where
elevations were determined. Nine months of q=incrcase in pressure at the foundation a construction period lasting one year had B=width of the loaded area
passed before the first survey on building A. E=modulus of elasticity
For building C the elapsed time was about p = Poisson's ratio
four months. p= influence value computed after
Steinbrenner (1934) depending upon shape of the loaded area, depth of
(5) Calcz~laleri Settlements the clay bed and Poisson's ratio for
the deposit. Total theoretical settleme
on the assuir~ption that they would be elastic Poisson's ratio was assumed to be 0.4, to in nature, since the total foundation pressure take into account some plastic deformation of in each case is considerably less than the pre- the soil. For the modulus of elasticity the consolidation load. The following equation initial tangent moduli were used as determined (from Skempton 1951) was used to determine from undrained triaxial compression tests the greatest settlenlent beneath the point of (Cooling and Gibson 1955, Simons 1957,
maxiinuin pressure which was assumed to be Ward et al 1959). The values shown in Table 1 the centre of gravity of each slab. are about one-half o easured maximum 9
settlcnicn t and a rathcr smallcr fraction of tlic actual maximum scttlcmcnt.
Tlicorctically, clastic clisplaccments sliould be i~istantancous witli tlic application of a load. If this did occur a t the tlirec buildings in question, somc other mechanism must also Iiave been a1 work, for it can be secn tliat the settlement continued to increase witli time for about four years following the co~nplction of each building. It must therefore be concluded tliat some plastic. deformation has also taken place.
Meyerhof ( 1 95 I ) suggests two simple approximate methods for calculating plastic settlements, both of which are based upon tlie deviation of the triaxial compression test curve from the linear relationship of stress vs strain represented by the initial tangent modulus. An attempt to apply these methods was un- successf~~l, for within the range of stresses involved the relationship of stress to strain for triaxial compression tests on Leda clay was
.,
not perceptively different from that expressed by the initial tangent modulus.
The discrepancy between measured and estimated settlements might be accounted for, in part, by tlie monhomogeneity of the clay and the necessity to extrapolate from the clay properties at a central borehole to obtain values for tlic calculations for each building. This is shown by the location of the pointsof maximum settlement, which in each case was some distance froin the centre of gravity of the
mat.
For comparison, further calculations of settlements were made based up011 tlie slope of the reco~iiprcssion branch of the pressure- void ratio curve. As can be seenfrom Table 1 these values are considerably grcater than the settlements measured to date. They are also much larger than ally value that might reasonably be extrapolated from the time- settlement curves in Fig. S.
TABLE I
Comparison of Measured with Calculated Maximum Scttlelnents
Maxiniurn Settlements
--
--Calculated (inches)
Building Measured up
(inches) Elastic Recompres- $ion
(6) Bearing Capacity
The general practice in Ottawa has been to use allowable settlement's as the controlling factor in designing foundations on the Leda clay, rather tlian use its safe bearing capacity. It appears that tlic permissible foundation pressures producing the maximum allowable settlements arc somewliat less than tlic bearing capacity based on the sliear strength of the soil. The allowable bearing capacity for a general shear failure in a clay soil (+=0 deg.) niay be expressed in the form given by Skemp- ton (1951)
where q=allowable bea-ing capacity F=factor of safety
c=cohesion or sliear strength of the soil P=total overburdeli pressure at founda-
tion level
where d=depth of footing
B=widtli of footing or foundation L=length of footing o r foundation
At site B, d = l 2 ft, B=70 ft, L--'107 ft, (4 111. by 21 m., by 33 m.), C=:O.56 TSF (0.56 kg/cm2). P=0.59 TSF (0.59 kg/cm2). Then N,=5.84. For the case where F = l (ultimate bearing capacity) q,,= 3.9 TSF (3.9 kg/cm2).
This figure agrees well with the ultimate bearing pressure of 4.0 TSF (4.0 kg/cm2) under the tower of the National Museum Building about 1500 ft (460 m.) away (Crawford 1953). The upper part of this tower had to be removed to prevent a bearing capacity failure of the foundation material.
Inserting a factor of safety, F = 3 as.sugges- ted by .Skempton (1951), q becomes 1.7 TSF (1.7 kg/cm2) causing
a
net increase in vertical stress of 1.1 TSF ( l , l k g / ~ m . ~ ) . Calcualated settlements based on elastic formulae would be 0.6; in. (1.3 cm) and from the slope of the recompression branch of the pressure-void ratio curves about 8.5 in. (22 cm).It may be noted that under building B
which had a net increase of vertical stress of 0.73 TSF, the maximum measured settlement was 0.5 in. (1.3 cm). As shown in Table I, the calculsted elastic settlements were about one-half this value and the calculated recom- pression settlement about ten times greater. Assuming that these proportions of calculated to measured settlements apply for the vertical stress of 1.1 TSF (1.1 kg/cm2) the resulting calculated settlement would be about 1 in. (2.5 cin). Due to the difference between theoretical and practical results, it is seen that further refinement in this type of calculation based upon safe bearing capacity is desirable. Conclusions
I . Even on such a sensitive soil as the Leda clay cf Canada, large buildings with uniformly distribu~ed loads may safely b: con- ~tructed by "floating" them by means of thick reinforced concrete foundatipn mats located
12
at a depth below original ground surface such that the reduction in vertical pressure due ru the soil removed is an appreciable proportion (up to unity) of the newly imposed total load.
2. Three large apartment buildings cons- tructed in this way in Ottawa, Canada, with increased net pressures on the clay varying from 0.54 TSF (0.54 kg/cm" to 0.73 T S F (0.73 kg/ cm2) have settled only about half an inch over a period of from 6 to 10 years.
3. In these buildings, differential settle- rneilts of the order of two-thirds of the maxi- mum caused no structural defects.
4. The settlements measured beneath the buildings were time dependent, even though the imposed loads were less than the precon- solidation load for the clay on which they were founded. It appears that both elastic and plastic soil moveineqt has occurred. Settle- ments calculated from elastic theory were about one-half the measured values.
5. Settlements calculated from the slope of the recompression branch of the pressure-void ratio curves for the soil gave values conside- rably higher than the actual values.
6. Foundations for buildings on clay similar to the Leda clay of Canada with uni- formly distributed loads that are to be supported by reinforced concrete mats b e l ~ w original ground level may be designed on the basis of the bearing capacity of the clay using a suitable factor of safety, provided an analysis of the settlement is also made.
Acknowledgements
The authors are indebted to the respective owners, architects and consulting engineers for permission to picsent the rcsults given in this paper, as also for the privilcgc of obscrv- ing the performance cf the buildings since their
constrution. Buildi~igs A and B are owned Morris Woolfson was tlic architect for tlie thrcc and were built by Mr. J.R. Beach and building buildings ancl MI.. G. C. McRostie was thc C by the Til'Fany Realty Company. Mr. J. consulting cngineer on soils.
Baracos, A. (1957). The foundation failure of Gadd, N.R. (1057) Geological aspects of the Transcona Grain Elevator. Reprinted Eastern Canadian flow slides. Proceedings from the Engineering Journal, Vol. 40, Tenth Canadian Soil Mechaliics Conference, No. 7, July 1957, Research Paper No. 42 National Research Council, Associate Com- of the Division of Building Research, NRC niittee on Soil and Snow Mechanics, Tech-
4501. nical Memorandum 46, p. 2-S.
Cooling, L.F. and Gibson, R.E. (1955). Settle- Gadd, N.R. (1960). Surficial geology of the ~ n e n t studies on structures in England. Becancour map-area, Quebec. Geological Conference on the correlation between Survey of Canada, paper 50-5.
calculated and observed stresses and dis-
placements in structures. Institution of ~ ~R.M., ~~ id ~c . ~ . l~(1954). ~ ,~ ,~ ~ ~ ~ d ~ ~ i ~ ~
Civil Engineers, Sept. 21-22, Paper 18, investigation of the Kitilnat Smelter. The
Group 4. Engineering Institute of Canada, Journal, p.
1460-1466. Crawford, C. B. (1953). Settlement studies on
the National Museum Building. Proceed- ings of the 3rd International Conference on Soil Mechanics and Foundation Engineer- ing, Switzerland. Session 415, p. 338-345. Also research paper No. 11 of the Division of Building Research, National Research Council, NRC 3071.
Crawford, C.B. (1060). Engiliecring studies of Leda clay. Paper presented to the Royal Society of Canada Symposium "Soils in Canada", Kingston, June 1.960.
Eden, W.J., and Crawford, C.B. (1057). Geo- technical properties of Leda clay in the Ottawa area. Proceedings of the Fourth. International Conference on Soil Mechanics and Foundation Engineering, Londoii. Section l a/6, p. 22-27; also Technical Memorandum 52, NRC Associate Coni- nitt tee on Soil and Snow Mechanics, January 1055.
Hardy, R.M. (1957). Engineering problem involvilig preconsolidated clay shales. Engineering Tnstitute of Canada, Transac- tions No. I , September; also NRC Associate Colnrnittcc on Soil and Snow Mechanics, Technical M e ~ n o r a ~ i d u ~ n No. 51.
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