Field study on the load-bearing capacity of ice covers

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NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

FIELD STUDY ON THE LOAD-BEARING CAPACITY OF ICE COVERS

by L.W. _Gold

ｾ･ｰｯｲｴ No.

192

of the

Division of Building Researoh

Ottawa November

1959

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PREFACE

The use of the frozen surfaces of rivers and lakes as transportation routes has become a commonplace of Canadian winterso One of the principal users of such routes is the pulp and' paper companies of Canada in their winter woods operationso These companies are therefore well aware of the hazards involved, but they have developed much experience in the safe operation of vehicles over such ice sheetso

The value of this experience was emphasised in the discussions of papers on the bearing strength of floating ice sheets presented at a special conference convened in the

BUilding Research Centre of the National Research Council in Ottawa in April

19580

The conference was sponsored by the NoRoCo Associate Committee on Soil and Snow Mechanicso The

papers then presented were published in a special issue of the Transactions of the Engineering Institutes Volo 29 Noo

3,

September

19580

It was decided that an attempt should be made to record this practical experience, so that it might be correlated with theoretical studies, thus advancing still further knowledge of this important phase of "fo e mechanics" which has such great economic significance o The Canadian Pulp and Paper Association kindly agreed to co-operate through their Woodlands Section, Mro WoAoEo Pepler s Managero A questionnaire was prepared by the author of this report and circulated to member companies of the Association who kindly co-operated and eventually returned completed forms containing much valuable informationo The

appreciation of the Nati,onal Research Councils and of the Associate Committee on Soil and Snow Mechanics in particular, is gratefully recorded for this fine helps

This report summarises the results of an analysis of this first winterDs set of field observationso It has been prepared by Mrs Lorne Wo Gold, who is the head of the Snow and Ice Section 'of the NoRoCo Division of Building Research9 and

chairman of the Snow and Ice Subcommittee of the ａｳｳｯ｣ｾｴ･

Committee0 In his paper, Mro Gold makes clear that his conclusions

are preliminary onlyo They are, however» of interest and ｳｩｧｮｩｦｩｾ

cance and point the way to the certain value of further field observations of the same characteTo It is hoped that those

responsible for the observations herein analysed will see that their work of last winter has been put to good use, and that they will be thus encouraged to continue ｴｨ･ｾｲ assistanceo

ottawa

November

1959

Robert Fo Legget Director

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FIELD STUDY ON THE LOAD-BEARING CAPACITY OF ICE COVERS by

L.W. Gold

Frozen lakes and rivers are widely used in Canada for transportation purposes. It is therefore of great importance to determine the dependence of the bearing capacity of an ice cover on the physical properties of the ice. Because of the complicated way in which ice behaves under stress, it is impossible at this time to calculate witrl confidence the bearing capacity of an ice sheet from the information now available on the elastic and plastic behaviour of iceo As is often the case in such circumstances,

recourse is made to the empirical approach. Those who use ice covers continuously for transportation purposes develop through experience a knowledge of the bearing capacity of frozen lakes and rivers. Unfortunately, this experience gained in the field is rarely recorded and therefore not generally available.

The Pulp and Paper industry make continuous use of frozen lakes and rivers in their logging operations. During a symposium on the bearing strength of ice held in Ottawa in

1958,

it was suggested that the experience of the logging companies in ｰｾ｣ｩｮｧ

loads on the ice should be recorded. This suggestion was acceptable to the logging industry and so during the fall of

1958,

with the assistance of the Canadian Pulp and Paper Association, the National Research Council initiated a field study on the load-bearing capacity

of ice.

A form was prepared upon which could be recorded the pertinent details whenever a vehicle or horse broke through the

ice cover. A second form was prepared which asked for the maximum load that was successfully placed on the ice and the associated ice thickness and quality. Copies of these forms were distributed to the Pulp and Paper companies through the Canadian Pulp and

Paper Association. This report contains a summary of the information obtained from the forms which were returned to the National Research Council during the winter of

1958-59.

Observations

In Appendix A are shown the forms that were distributed. The information obtained from these reports is summarized in

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2

-in the reportso No attempt ｷｾｳ made to take into account wheel spacing when calculating the effective load on the ice. It was thought that this refinement was not warranted at this time.

In calculating the effective ice thickness it was assumed that 2 inches of white ice was equivalent to 1 inch of good "blue" ice. For example, if the measured ice thickness was 30 inches, of which 10 inches was white ice9 the effective ice thickness was recorded as

25

inches.

In Figo 1, the Loger-Ithm of the observed load is plotted against the logarithm of the effective ice thickness. The meaning

of the symbols used is given with the Figureo Some of the experience criteria used by various companies to determine the safe load for ice of given thickness was available.* This information is also given in Fig. I.

Discussion

Theoretical considerations show that the bearing capacity of an ice sheet is proportional to the square of its thickness. Lines showing this dependence for two proportionality constants are drawn in ｆｩｾｯ I. It is seen that all observations lie below the line given by

h

=

150

P

where h is the thickness in inches, and P is the load in tonso If only the maximum loads placed successfully on the ice and the experience criteria are considered for loads greater than

15

tons_v then half of these observations were made on ice with a thickness greater than that defined by

h =

11607

P.

The observations indicate that factors which vary both with time and with location at a particular log storage area affect the bearing capacity of the ice. A number of the breaksthrough occurred at locations where the ice was thinner than on the remainder of the

lake or river for reasons such as localized water currents or "hot spots" on the lake bottom. In some ca se s the speed of the vehicle

ｾｽ The author is indebted to Mr. C.R. Silversides for making this information available to him.

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3

-may have been too high for the local ice conditionso The obser-vations plotted as solid triangles or x's fn Figo 1 are cases where factors that could have contributed to the accident were

observed and recordedo

The observations plotted as x's in Fig o I are of particular interest e In these cases the ice failed by "punchinglt_o _{The nature}

of the breakthrough and the low air temperature which prevailed at the time of the accidents would suggest that the ice may have

developed cracks due to thermal stressingo These cracks could decrease the effective thickness of the ice coverso

A sudden decrease in air temperature can cause high thermal stresses to develop in the ice if it is not adequately insulated by a snow cover o Many operators are aware of this fact from experience0 In one maximum load report the observer stated that

in their operations, extreme caution is used when mild weather is followed by extreme colde It is possible that thermal stresses develop when there is an appreciable drop in air temperature

especially toward the end of the daYe Conclusions

The number of observations available is not yet sufficient; to be used as a basis for empirical rules giving the de pe nde nc e of the bearing capacity of the ice on its thickness and other properties0 The breakthrough reports indica te that the ice cove!"

is sUbject to natural variations in its effective thickness₉ quality, mechanical strength, and possibly other properties that can have a very marked effect on its load-bearing capacityo

Reconnnendations

It is recommended that the recording of pertinent infor= mation for each failure of an ice cover under load should be continuedo Every effort should be made to make the information

as accurate and as complete as possibleo The report should contain

additIonal information such as the presence and nature of any cracks near the location of the breakthrough and whether there

was a marked decrease in the air temperature prior to the accidento

It is also recommended that experience criteria on the loads which the pulp and paper companies allow on the ice cover during the making of a log storage area and during its use should be recorded along with the associated ice thicknesse This record

should also include a description of the steps taken in the construction of the storage area and any special experiences directly concerned with breaksthrougho

The author is indebted to members of the Snow and Ice Section for their helpful discussion and comments during the preparation of this report.

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T • Truok

H • Horee Treo Traotor

B • Bombardier

ｾ

PULP AND PAPER SllRVEY OF BEARING STRENGTH OF ICE RESULTS FROM BREAKTHROUGH AND MAXIMUM LOAD REPORTS

VEHICLE WEIGHT (tons) ICE THICKNESS (1n.) SPEED SNOW _ｾｾｾＮ SYMBOL REfI"'RKS (mph) DEPTH (in.) Fi". 1

VEHICLE ILOAD ITOTAL MEASUREDIWHITEIEFFECTIVE

•

Tr 3

-

3 )

-

₃ ₅ 10

T 5.5 9.6 15·1 15 6 12 3 2 10 _A 20' from shore, lake shallow,

bottom "hot".

--T 3 6.5 9.5 8 4 6 parkad 3 0 _A Parked 1 min, baoked off slushod ares,

rear wheeJ3 went through.

H

-

0.8) 4 2 3 7 15 Ica broke in front - horsG went in head first.

B 2.3 1.5 3. 8 4 8 8 5 2 20 _A On narrow pi ver near- bank" ioe

underlain by nir apa ce ,

T 4 4.5 8.5 12 9 7.5 10 2 6

,

Tr 8

-

8 12.3 1·3 11.5 1 0 -10

•

Creek landing, soraping 10e.

B 1.5 1.b 3.1

-

5.5 3 ｾ -5

,

Travelling on creek, ioe thioknees var1ed between 1 and 10 inches. T 8

-

8 13 1 12.5 1 2 -10

_•

Creek4sndlng - soraping road_ water

depth 'max.

H -

-

0.7 6 4 4 0 -10 Scraping 10e, water level o bangf.ng , f---.

0.85 6 4 4

H

-

0 -10

T 10 13.5 23.5 27 11 21.5 12 0 -1 Lake shallow, "hot" bottom, depth 20', A week of +35°F followed by _2°F

2' snow off road note s need , B 1.4

-

1.4 3 2 2 8 6 5 A 3'1 1ce ran from sink hole to ahara

20' ahead and behind vehl01e Q" 10e. B 1.4

-

1.4 7 4 5 5 4 -20

_•

T 5 8.7 14.7 18

-

18 35 5 15 _{［･ｾｾｾ｡Ｌ､ｾ［ｾｯｾｾｾｾｧｾ･ｾｬｾｩｾｾ} 50' further

A rear sunk

to platform level.

H 0.75 3. 2 3·5 5 3 3.5 2 30 Double layer of ice with 2" between. Tr 1.65 0.35 2.0 8

-

8 7 3 -30

,

Pulling empty tank, tank did not

Igo throul>:h.

B 1.7 1.7 14 ') 8.5 parked 5 -10 1)ouble layer of ico with 3" WAter

etwesn parked 1 mfn ,

T 5.5 11.25 16.75 19 0 19 10 0 -35 X ｾｯｴｨ rear ｷｨ･･ｬｾ went through.

T 3.8 9.0 12.8 19 0 19 20 0 -35 X One rear wheel went through. T 4.15 9.0 13.15 22 0 22 parked 0 -35 X One rear whee 1 went through, parked

or 2 minutes.

T 4.15 10.25 14.4 20 0 20 parked 0 -25 _X One rear wheel went through, parked or 2 minutes.

T 5.65 9.0 14.65 22 12 16 5 0 0 X One rear wheel went through. T 5.6 10.25 15.65 19 0 19 5 0 -35 X lone rear wheel went through. H 1.6 2.3 3.9 4 2 3

-

8 -20

•

H 0.75 1.0 1.75 4 0 4

-

6 10

•

H 0.9 1·35 2.25 6 4 4

-

2 8

•

T 6.5 11.0 17.5 21 12 25 parked 4 -10

•

Parked 2 minutes. T 6 11.0 17.0 6 3 4.5 1 2 -10

•

T 5 8.25 13.25 4 0 4 1 4 -5

•

T 4.2 1.5 5.7 17 8 13 1 3 -12

•

T 5 10 15 22 12 16 15 2 -10 A

T 5 13.5 18.5 21 4 19 parked 4 20

,

Side of truck olosest to shore went throulLh• Water level ohangin". T 4.5 0 4.5 6 2 5 5 2 -10 _A \ocldent on river. 100 feet from truok

18ft _ice.

T 4.5 12.5 17.0 18 4 16 parked 3 10

,

Ioe in 2 layers wlth 2" water between, rear end went through.

T 4.0 13.5 17.5 18 6 15 5 2 10 _A Ioe In 2 layers wl th 2" water botween, rear end broke through.

Tr 2.75

-

a.75 8 4 6 2 8 15

,

Went through "werm hole". Ioa 14" thiok around p1aoe where traotor ssnk. '1' 5.4 13.5 18.9 19 8 15 8 1.5 -22

,

Heaviast of 30 100ds already passed

over. Ioe surrounding about 22· thlok. T 6 16 22 17 13 10.5 5 2 -30 A Ioe In 2 layers wlth 2" water

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T

=

Truck Tr

=

Tractor TABLE II ｾｾｘｉｾｉｄｍ LOAD REPORTS Weight (tons) ｶ･ｮｩ｣ｾ･ I Load I Total Remarks T Tr 10 17.2 25

I

I I 35 17.2

I

! 33 I , ! 32 •1 i 7 1c::' r: --./'

..

-30 :3 I26

I

36 6

I

33

I

3 ! 23 i 0 I20

I

23

-27.75 46.25 52 ＴＱｾＮＱ 2[;.20 20 31 13 2LL03 I t")_{v ... /}ｾｾｩ I I 13.9 I 30 I 9 L ; . 13 10.25 ,'3.85 I 12 11 l I 18 I

I

14.0

I

16.25 ! 11 I T' T T T T T T T T T i mec e s sar-y , T

!

_15.65 _[-26-:-65

42.io

.1

_2h-h2 ₅ _i_21.5-39.5

I

₂ _I T I ,.J

5

I - r

5

I .... T I I ' l' 11 1:::;>.

I

20. 30 I 1iJ ! 21 ! U I T

5

I 26 I 31 I 30 I 1S !21 30 I T I 28 I 37.4 I 65.4 33 I 26 I_J 25 _{_ _}

I

_• 0 I I i I I ｾＭ - - - , - : T i 7

I

15.0

I

22.0

I

30

I

15 12 2 • 5

i

4 :

I

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•

• ICE FAILURE, GENERAL

& ICE FAILURE, NOTE REMARKS

AND VEHICLE SPEED, TABLE I.

x ICE FAILURE UNDER LOW

TEMPERATURE CONDITIONS.

n MAXIMUM LOAD REPORTS

o EXPERIENCE CR ITERIA n • 0 0 0

x

a of..,.,

DO x ｾ［［ｵＮｯ｣ a 0 h • 7·1

.;p-

x &X X & 0 0 11&& P=0'06h 2 - - - , "_o u _h=4'2"Pｾ

• _•

•

10'0 0 0 9·0

B'O & &

& 7-0 0 6·0 0 & &

•

5·0 De 4'0

•

3'0

•

2·5 2·0 1-5 30 25 ｾ 20 100 BO 60 50 40 s= 15 (J) (J) w Z :lI:: o X

....

W U

-1-0 "'-_---'-_...---r._.l.--.&...I...I-I-.--I-...I-..r...I._ _..._ ...- - - ' - - . l ...,,_ _... I 1·5 2 2·5 3 4 5 6 7 8 9 10 15 20 25 30 40 50 60 80 100 LOAD P (TONS) FIGURE I

THE LOAD ON THE ICE AND THE ASSOCIATED EFFECTIVE ICE THICKNESS

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APPENDIX A

FORMS FOR RECORDING INFORMATION ON ICE COVER

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A-2

National Research Council

Associate Committee on Soil and Snow Mechanios VEHICLE BREAKTHROUGH REPORT

Date Time of day

Company Division __ｾ __

Vehicle Make Year

---Model Tire Size

Semi Trailer Yes

a

No

0

Estimated weight of vehicle (empty) lbo

Estimated total pay load lbo

I

If load is wood, estimated number of cords

Estimated speed of vehicle at time of breakthrough -= =<=0 mpho

If vehicle was parked, estimated length of time parked __

Breakthrough sudden Yes

a

NoD

Measured total ice thickness (including snow ice) Measured thickness of snow ice (white ice)

ino ino Ice thickness is best obtained by removing a block from the water and measuring directlyo If this is not possible, obtain a straight piece of heavy wire and make a right angle bend at one and , The bent; section should be at least one foot longo Lower this bent section into the water and draw gently up against the under surface of the iceo Note on the vertical section of the wire the level of the ice surface and thus the total thickness of the iceo

Estimated average depth of snow cover on the ice Estimated average air temperature during

24

hour

period before breakthrough

in"

Remarks

To aid in evalu9ting the observations, all information available on axle spacing, number of axles, number and location of tires, would be appreciated.. Any unusual features about the breakthrough should also be noted.. Remarks and any sketches are to be placed on the back of this form ..

This form to be sent tOg

11 July 19580

Secretary,

Associate Committee on Soil and Snow ｍ･｣ｨ｡ｮｩ｣ｳｾ

National Research Counoil$ Ottawa, Ontarioo

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Associate Committee on Soil and Snow Mechanics HORSE AND SLEIGH BREAKTHROUGH REPORT

Time of Day . ..,..- _ Division

---____lb. _ _ _ _ _ _ _lb. _ _ _ _ _ _ _ _ lb. Date Company Weight of horse

Weight of Sleigh (empty) Weight of pay load

Estimated number of cords

Give dimensions of runners in sketch below

Did cracking occur before breakthrough Yes

a

No

L:J

in. in.

Estimated average depth of snow cover on ice in.

Estimated average air temperature during

24

hour period before breakthrough _

Remarks:

Please note any unusual features concerning the breakthrough. Indicate which part of the load or horse went through first.

This form to be sent to: Secretary,

Associate Committee on Soil and Snow ｍ･｣ｨ｡ｮｩ｣ｳｾ

National Research Council of Canada, Ottawa, Ontario.

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A-4

Associate Committee on Soil and Snow Mechanics MAXIMUM LOAD REPORT

The Subcommittee on Snow and Ice of the Associate Committee on Soil and Snow Mechanics would like to obtain for their study on the bearing strength of ice, information on the largest load which was

safely transported over an ice cover during your operations for the current season. We would be grateful if you would fill out the attached report and return it to the

Secretary,

Associate Committee on Soil and Snow Mechanics, National Research Council,

Ottawa, Ontario.

Company Division

---Vehicle Make Year

---Model Tire Size

Semi Trailer Yes

D

No

0

_ _ _ _ _ _ _ _ _ Ln , _ _ _ _ _ _ _ _ _ _ _ _ _in.

_____________. lb.

________________________lb. Estimated weight of vehicle (empty)

Estimated total pay load

If load is wood, estimated number of cords

Ice thickness is best obtained by removing a block from the water and measuring directly. If-this is not possible, obtain a straight piece of heavy wire and make a right angle bend at one end. The bent section should be at least one foot long. Lower this bent section into the water and draw gently up against the under surface of the ice. Note on the vertical section of the wire the level of the ice surface and thus the total thickness of the ice.

Estimated average depth of snow cover on the ice __________in. Remarks

To aid in ･ｶ｡ｬｵ｡ｴｩｾｧ the observations, all information available on axle spacing, number of axles, number and location of tires, would be appreciated.