Soil Mechanics Research on St. Lawrence Seaway: DBR 1956 Field Program

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Technical Note (National Research Council of Canada. Division of Building Research), 1957-01-01

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Hamilton, J. J.

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DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA

'fECHNIICAlL

NOT FOR PUBLICATION

NOTlE

No.

217

FOR INTERNAL USE

ｾｐ］ｒ］ｅｾｐａｾｒｾｅｾｄｾｆｷｏｾｒｾ St., Lawrence Seaway Authority

Soil Mechanics Research on ｓｴｾ Lawrence

ｓ･｡ｷ｡ｹｾ DBR

1956

Field Program

PREPARED BY J <>J 0 Hami 1 ton

SUBJECT

CHECKED BY . _{APPROVED BlioFoLo}

DATEJanuary.:

1957

ｾ

This note outlines the ｳ｣ｯｾ of the

1956

field program of the co-operative research venture between the St. Lawrence Seaway Authority and the Division of Building Research, National Research Council ..

After several meetings at which Messrs., Peckover, Thorley, Hurtubise and Coates (representing the ｓｯｌｯｓｯａｾＩ and Messrs ..

Crawford"p Eden and Hamilton (representing De-BoR-o, NoR"C .. ) discussed the proposed ｣ｯｾｯｰ･ｲ｡ｴｩｶ･ research program» and after a period of orientation on the Beauharnois construction site by Hamilton, certain definite objectives for the fall and early winter period were developed; these may be summarized as followso

Development, Calibration and Comparison of Field Vane Testing Equipment for Use in Leda Clay

The field vane ｡ｰｰ｡ｾ｡ｴｵｳ provides a method by which the shear strength of a cohesive soil may be measured in situ o It

offers considerable advantages in both cost and time over laboratory strength determinations from tube sampleso Since the Soil Mechanics Sections of both DoBoRo and SoLoS ..Ao are actively interested in

the development and evaluation of field vane apparatus for the testing of sensitive and ･ｸｴｲ｡ｾｳ･ｮｳｩｴｩｶ･ ｣ｬ｡ｹｳｾ it was agreed that work in this field would be of definite value to both organizations .. Both the DoBoRo and the SeLoSoA" possess field vane equipmento

The S.,LoSoAO: vaIle is a commerical apparatus made by the

ｾ｣ｫ｡ｲ Drill Co. The torque applied to the vane through the vane

rods i·s measured by a torque wrench.. ｾｨ･ rate of strain applied to the vane is controlled roughly by turning the torque wrench at the rate of one degree per second.

The NoR .. C. vane apparatus was made from designs used in England and by the HoEoPoCo of Ontario" The vane is attached to

standard drill rods. The torque is applied through a gear drive mechanismo The amount of torque is measured by the reaction of the

2

-gear drive on a dynamometer. The gears are driven by turning a hand crank at a constant ｲ｡ｴ･ｾ giving a rate of strain of six degrees per minute.

The testing program was ｵｮ､･ｲｴ｡ｫ･ｮｾｾ

(a) to develop a standardized field testing technique; (b) to modify existing apparatus if necessary, to improve

its performance;

(c) to evaluate its practical applicability in Lada clay» (d) to compare techniques and results with various types of

apparatus; J

(e) to obtain data on the shear strength of Leda clay; 'and (f) to obtain an indication of the economic aspects of this

type of testing.

Work with the Acker vane equipment of the

st.

Lawrence Seaway Authority was s.tarted early in Ootober at the site for tne Cornwall Island approach to the proposed International bridge crossing the South Channel o.r the Sto Lawrence Rivero Several test borings were made on the island with control tests being made adjacent to sample boreholes from which Amerlcan engineers had obtained samples for triaxial shear strength testipgo During' this period, a standardized testing procedure was adopted and minor improvements in the apparatus were madeo Test results

from the Aoker vane borings and from the laboratory testing 'program of the American ･ｮｧｩｮ･･ｲｾ are now avai la ble in both DoB oR0 and

SoLoSoAo fileso .

During the last week of October and the first week of

November the Acker'vane equipment was used at the Caughnawaga site where its application in testing very weak» shallow deposits of clay was further investigated.

The Acker vane apparatus was tpen moved to the Upper

Lock Area9 Beauharnois,l where test borings Noo

643A

and B,l located

respectively

4

feet west and

3

feet east of the originalSoLoSoAo sample bor ing No0

643»

were ca'rried out0 The main purpose s of

these borings were: to check the reproducibility of results obtained when using the Acker equipment; to study the practical depths to which hand operated equipment could be operated; and to

- 3

ｾ

compare field vane shear strength values with values of shear

strengths already obtained in the laboratory by means of unconfined and triaxial compression tests carried out at Ecole ｐｯｬｹｴ･｣ｨｮｩｱｵ･ｾ

Montreal0

Two additional Acker vane borings,Noo 623D and E_{p were}

made a short time later to substantiate further the ｲ･ｾｵｬｴｳ of the two previously mentioned borings and also to ｾｩ･ in with the two NoRoCo vane borings, Noo 62)B and C_p and with the NoRoCo piston

sampling borehole Noo 623Ao Boring Noo 6a3D was located

4

feet west of the original SoLoSoAo boring Noo 623, while Noo 623E was

located

4

feet east of boring Noo 6230

From November 19th to November 23rd the two NoRoCo vane borings NoD 62)B and C were completedo These borings were located respectively

4

feet northp and

4

feet north and 6 feet west of the

original SoLoS.AD sample boring NOD 623. The objectives of these two borings ｷ･ｲ･ｾ to optain shear strength values for comparison with the Acker vane results and laboratory test results; to evaluate the effects of using vanes of different area ratios on strength

values obtained for the same material; andp to investigate the

significance of rod "friction" in vane testingo Results

When reviewipg the results of the program to date, it must be remembered that this is essentially a progress report a.nd there-fore the results are preliminary; they will of course be subject to revision as further experience dictateso

(i) A tentative standard ｦｩ･ｬｾ｟ｴ･ｳｴｩｮｧ procedure has been drawn up and copies of this are available in both SoLoSoAo and DoBDRo files;

(ii) The most significant modification made to the Acker vane testing ･ｱｵｩｰｭｾｮｴ was a vane protective housing which was designed and constructed and has proved satisfaotory in a limited ｾｵｭ｢･ｲ of tests to date. Tbe primary purpose of this housing was ｾｯ protect the vane while it was being advanced, in the hope that the problem of

ｾ bending of vane stems would be eliminated;

(iii) Work with the Acker vane equipment to date indicates that it is a fast efficient means of in situ shear strength testing in purely cohe-sive soilso By hand operated teehniquesp its efficiency

ｾ

4

-is possible with slightly lower efficiencyo Beyond 30 feet, difficUlty is encountered in augering a hole either by hand or with power operation}

(iv) It is believed that the use of the vane protective housing will allow driving of the vane to advance it to the greater depths without damage to the vane since it was found possible, under

favourable conditions, to complete a boring to refusal at

42

feet in one working day with a crew of three meno The favourable

conditions mentioned include equipment being at the site ·at the beginning of the day, and no difficulties being encountered with bent vane stems or similar equipment failureso The experience of the crew tncreased the efficiency considerably»

(v) The plotted results of all the Acker vane and NoR.e. vane equipment are included in the data in SoL.SoA. and NoRoCo files, along with a discussion and calculation of ｾｴｨ･ theoretical rod friction corrections for these testso Examination of these test results indicates that further work on this factor in NoRoC. vane tests is necessary;

(vi) In situ shear strength values obtained with the NoRoCo vane indicate generally thatg .

(a) within reasonable limits, there is no appreciable difference between shear strength values obtained with a large ratio vane apparatus, and those obtained with a small area-ratio vane»

(b) there is a definite advantage in keeping the vane stem rod as small as possible, since its diameter definitely ｾｦｦ･｣ｴｳ

the rod friction correction which must be applied to readings, especially in clays of lower sensitivity; and

(c) in situ shear strengths measured with the NoRoC vane apparatus are, in general, equal to or slightly higher than those measured with the Acker vane apparatus. This may indicate that

the Acker vane calibration formula is on the conservative side, (vii) Plots of shear strengths by vane apparatus and unconfined and triaxial compression tests with depth are included in the data already in SoLoSoA o and DoBaR. fileso These plots indicateD as have other similar investigations in Lada clay deposits made by DoBoRo, that only the highest shear strength values obtained from unconfined compression tests agree with in situ vane tests D while the majority of shear strength values from unconfined and triaxial compression tests (Which showed significantly high strains at

failure) are much lower. It is believed that disturbance on sampling, causing partial remoulding of the tube ｳ｡ｭｰｾｳＬ is the reason for these ver'J' low shearing strength values,g

(viii) The field vane tester seems to offer an economical means of augmenting shear strength data in clay which has been adequately ident ified" and cIa ssified by means of a limited number of

"undi sturbed" sample borings0 The time required to complete a

field vane boring is considerably less than that required for a careful "undisturbed" piston sampler boring;

(ix) It is estimated that the, time required to obtain in situ shear strengths' with the vane apparatus would be from 1/2 to 1/3 the time reqUired to do "undisturbed" sampling to the same deptho The expense of time and equipment necessary for the laboratory

testing of samples must be added to the time required for sampling; (x) It is important that field vane testing be done only in deposits of material which have been adequately identifiedg so that the effects of weatheringg or strata of other than purely cohesive

soils on the vane test resultsg can be recognized and evaluatedo Study of the Geotechnical Properties of Leda Clay

The study of t he engineering propertie s of Leda c lay is

one of the research programs being carried out by the Soil Mechanics Section of DoBoRo Since sizeable deposits of this material are

located at various construction sites along the sto Lawrence Sea=

waYg notably at the Upper Lock Area at Beauharnois g it was agreed that a program of careful sampling in the field and extensive

laboratory testing would be of mutual ｢･ｾ･ｦｩｴｯ In particularg this

sampling would allow:;a comparative evaluation of the sampling and laboratory testing techniques employed by the two organizations

and would provide a further basis for evaluation of field vane testso From November 8th to November 17th the NoRoCo drill rig

and piston sampling equipment were employed in obtaining samples which included one of the "weathered crust" and twelve samples from

161=6"

to refusal at

43

1

=9"

to give a complete profile of the

Leda clay deposit in the Upper Lock Area o This boring g NoD

623A

was located

4

.feet west and

4

feet north of the original SoLoSoAo sample boring NoD 623 and therefore was also adjacent to the two Acker vane and t he two NDR oC 0 vane bor ings0

The WORk with the piston sampler was slow but it is expected that the samples obtained will be satisfactory since extreme care was taken throughout the ｳ｡ｭｰｬｩｮｾ operationso Good recovery was generally noted with only one sample being losto The loss of this sample from

36

n

_=6"

_to

₃₈

i

=6"

depth_g was attributed'to disturbance

6

-The results of this phase of the ｰｲｱｧｾ｡ｭ will not be known until the extensive laboratory testing program which is planned for these samples has been completedo This program of testing is scheduled for the winter period at the Soil Mechanics Laboratories of the Division of Building Research and is expected to be completed by the end of February 19570 The samples wi11 be tested for moisture content» Atterberg limits, unit weight.

specific gravityv grain sizev uncoqfined and triaxial compressive strengthsv salt concentration» consolidation, and sensitivityo

Conclusions

10 The SoL.SoAo and NoRoCo vane shear strength determinations appear to be comparable.

20 The field vane strength determinations are consistent, and appear to be a better indication of shear strength than strength determinations made from tube sampleso Only the maximum values obtained from tube samples are equal to vane shear strengtho

30

The field vane tests offer many advantages in time and economy. 40 Attempts to obtain undisturbed piston samples were successfulo Comprehensive testing will be conducted on these samples to establish various geotechnical relations for the Leda clay.