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Mechanical and structural properties of ice Ruedy, R. R.

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MECHANICAL AND STRUCTURAL PROPERTIES OF ICE

Two literature reviews prepared by R. R. Ruedy during an investigation of the properties of ice carried out in 1943 under the direction of the National Research Council of Canada

Internal Report No. 395 of the Division of Building Research

Ottawa February 1972

··.i ''' .•, ｾ .....""". PREFACE

The possibility of major oil and gas developments in Northern Canada, particularly in offshore areas, has brought about an increased interest in the behaviour and properties of ice. This interest is not confined to the forces that ice covers might exert on structures, al• though this is a major problem. Ice covers can also be used as sur• faces for roads and airstrips, and consideration is being given to their use as platforms for drilling operations.

In 1943 the National Research Council of Canada undertook, with the assistance of several university and other groups. a major investigation of the properties of natural and reinforced ice. At the conclusion of the war the information obtained in this study was assembled in the Council's files. Some of it is relevant to current interests and needs, and it was decided to make it available for limited distribution in the Internal Report Series of the Division of Building Research.

The present report contains two literature reviews prepared by R. R. Ruedy, who was a member of the staff of the National Research Council. The first is on the mechanical properties of ice, and considers Young's modulus and strength. Several topics are considered in the second review, including effect of salts, properties of sea ice. viscosity and plasticity of ice and aspects of ice engineering. These are presented just as they were prepared in 1943, without revision. They still form an excellent starting point for a study of the subject, to be updated as required by the reader through reference to more recent literature.

Also included in the report. as Appendix A, is a summary of selected technical data on ice obtained from the investigations and thought to be of current interest. Further selections will be made for reproduction in subsequent reports.

Many individuals participated in the field and laboratory research associated with this wartime activity. The Division of Building Research is honoured to have this opportunity to make the fruits of their efforts available for application to present-day problems of national concern.

Ottawa N. B. Hutcheon, February 1972 Director TABLE OF CONTENTS

Page

PART I. MECHANICAL PROPERTIES OF ICE 1 Introduction 1 Young's Modulus for Ice 3 (a) General Features 3 (b) Young's Modulus from Compression Tests between the Freezing Point and Zero Degrees. Progressive Loading. 3 (c) Young's Modulus for Bending Stresses (Progressive Loading) 5 (d) Young's Modulus for Decreasing Loads in Bending Tests on Beams of Ice Prepared from Frozen Snow 5 (e) Young's Modulus from the Velocity of Sound in Ice (Adiabatic Value) 7 {f} Miscellaneous Values for E 7 (g) Rigidity of Ice and Poiaaonts Ratio 7 Strength at Failure 8 {a} General Features 8 (b) Crushing Strength of Ice 9 (c) Tensile Strength of Ice 10 (d) Strength of Ice in Bending 11 Impact Strength of Ice 12 (a) Strength in Sudden Loading 12 (b) Shifting Loads 13 (c) Impact Strength 13 Page

PART II. STRUCTURAL PROPERTIES OF ICE Effect of Salts 15 The Production of Large Single Crystals 18 Heat Conductivity 19 Ultimate Strength of Ice in Shearing 20 Internal Friction (Viscosity) of Ice 21 Experimental Work on the Adhesion of Ice 21 Ice Floes as Landing Fields for Aircraft 24 Properties of Sea Ice 28 Ice in Excavation of Shafts and Tunnels 29 Reinforced Ice as Structural Material 32 Coefficient of Linear Expansion of Ice 33 Temporary Supports of Ice 33 Ice as a Building Material 34 Destruction of Ice Masses by Explosions 34 Plasticity of Ice 35 References 39 Appendix A

Note: The material in this report refers to a small number of tests and the results cited are not to be taken as average values. PART 1. MECHANICAL PROPERTIES OF ICE INTRODUCTION

Ice differs in several respects f r orn other rnater ial s of COITlITlon occurrence. Metals and stones are aggregates of s rrial I grains. and SOITle of their properties differ quite rnar kedly f'r orn those of single crys• tals of the s arne rnater iaI, Ice. whether gathered f r orn lakes and rivers or produced artificially, consists of a few large crystals. and the prop• erties of ice consisting of rrrinute grains ar e only irnpe rfectly known f r orn studies on glaciers and scattered tests on icicles and snow. The question of grain size that plays such a large part in m.eta.Hurg y, creates therefore little difficulty in the study of blocks of ice. When ice grows undisturbed on the surface of large water bodies or in srna.Il vessels. the optic axis or axis of the hexagonal p r i srri, is always perpendicular to the surface of the ice-cover, except near the edges and in the first stages of freezing. As a result of the presence of large single crystals of the hexagonal s y s tern, the properties of ice depend on the direction considered, in particular on the direction parallel to the base of the p r i srn, or parallel to the sides of the prism, that is. parallel to the optic axis and the direction of undisturbed growth. Roughly speak• ing crystals of ice behave as if they were built up of an infinite numbe r of very thin sheets of paper fastened together with SOITle viscous substance that allows the sheets to slide over each other when strong forces are applied parallel to the sheets, or in other words, perpendicular to the optic axis. The single sheets are nearly inextensible and quite flexible. On account of the iITlperfect c ementation of the sheet, d i spl.ac ements in the for m of punching are readily produced parallel to the base. When, for instance. bars of square cross-section (1 sq. CITl.) with the optical axis parallel to the length of the bar, are placed upon wooden supports, and a cord carrying a weight of about 5 kgrn, is slung around the section between the supports, a piece corresponding to the thickness of the cord is gradually pushed downwards. No cracks occur in the bar, but the dis• placed piece is streaked with fine lines parallel to the base of the hexag• onal crystal. On the other hand. since the crystal planes ar e flexible. a rod will bend under its own weight when the optic axis is perpendicular to the length of the bar and the sheets of paper are horizontal, but if the bar be turned over so that the basal planes are vertical. the rod is rnor e dif• ficult to bend even when loads are applied. Another irnportant difference between ice and COITlITlon engineering rnater Ials is that stones and rne ta.ls are used at a ternpera ture farther be• low their melting and softening points than ice ever is out of doors. Ice. therefore, is in an even less stable state than rnetal s and stones are. and the ternpera ture must be expected to exert a strong influence upon its rnechanical properties. This variability is enhanced by the peculiar in• fluence of the pressure upon the rrrelting point of ice. - 2 -

Melting Point of Ice at Various Pressures

Temperature I Pressure TeITlperature Pressure of °e *kgITl. per I lb. per of °e ｾＧ＼ｫｧｉｔｬＮ per I lb. per I• I. sq. CITl. ! sq. rn, sq. CITl. , sq. In. I I 32 0 1 ! 14 -12.5 1410 ,I 20, 064 2.5 336 4, 781 5 -15.0 1625 23, 124 23 5 615 I 8,751 -17.5 1835 26, 112 I - 7.5 890 112, 665 -4 -20.0 2042 29, 058 I 14 I -10 1155 :16,436 -22. 1 2200 31, 306 I

At terrrper a tur e s not rnuch below freezing a relatively s rriaII pressure would be sufficient to rne It the ice at the points of greatest pressure. The foot of a c olurrm or pile of ice, 15 rne t r e s to 20 rne tr e s high, ought to show signs of m elting even though the whole c olurnn is at a terrrper a tur e a few degrees below freezing. A few towers of ice of this height have been built as showpieces, but the walls were rriad e 33 inches thick and the base offered a large resistance to flow and gliding.

The general rnecharrica l strength of ice is Lirni t e d by another property of the point of fusion of ice. When pressure is applied to ice that is colder than -20 0 e or -30 o e and therefore much stronger than ice near the freez• ing point, and the pressure is increased to 2, 250 kgm, per sq. CITl. on all sides, new f or rns of denser ice form., narne ly Ice III (at ternper a ture s be• tween -30° and -50 oe ) and Ice IJ.. slightly denser than ice III (between -70 0e and -30° e). On account of these transforrnations the resistance and ex• pansive force of ice is Hrni.ted; the pressure exerted by ice cannot exceed about 2, 500 kgrn, (35,560 lb. per sq. in.), since at this pressure occurs the change to denser f or m s , At very low temperatures Ice m and Ice II are obtained at ordinary pressure, and on war m.ing Ice III f r orn the teITlper• atures of liquid air to -130 ° C it is transfor m ed into ordinary ice as shown by the change of the c ornpact pieces into a fine rneal of considerable v oIurn.e , Only ordinary ice shows a lowering of the rne l ti.ng point by increase in pressure. Above the freezing point, water can be kept solid by raising the pressure to 6, 300 kgrn, per sq. crn, and by increasing the pressure by about I, 000 kgrn, per sq. CITl. for each increase of 5 ° e in temperature.

* kgm, = kilogram - 3 -

YOUNGS MODULUS FOR ICE

(a) General Features On account of the card-pack structure of single ice crystals, ice is not elastic except for extremely small and unimportant loads. With ice, the value of Youngt s modulus depends on the successive increments of load; furthermore, the deformation under any load increases as the loading is sustained, and Young! s modulus decreases in proportion. To render measurements by different workers comparable, a standard method of loading would have to be adopted. At present results are available for loads of very short duration, for loads applied for a few seconds and in• creased step by step, for decreasing loads, and for loads sustained for hours or days. In general, when a cube of ice of about 5 -inch side length is loaded for the first time at 28 0 F with 10 lb. per sq. in. and the load normal to the optic axis is sustained for not more than five minutes, there is com• plete recovery on removal of the load. After the first and second re• petition of the test, and also when the first period of loading is lengthened, recovery is not complete. About 40 per cent of the total change in length, 25 millionth of an inch per inch length for a load of 10 lb. per sq. in., re• mains when the load is removed. A permanent set in the same ratio is found when loads of 20 or 30 lb. per sq. in. are applied. When a load of 20 lb. per sq. in. is allowed to act upon the block, the block yields continuously for about 3 hours 30 minutes and retains 90 per cent of its deformation when the load is removed (total elongation 250 millionth inch per inch length). Different values are found for other loads (Brown). Progressive deformation is also found with rods of ice prepared by freezing snow mixed with water and consisting of coarse grains rather than large crystals. When such a rod, 14 crri, long and 6 sq. crn, in cross• section is subjected to a compression or a tension lasting for about two months, the load being 2 kgrn, per sq. crn,, the average temperature _50 C (23 ° F), the rod increases 0.74% in length in 30 days when tension is applied, and decreases 0.37% in length when compressed. When the applied pressure is varied, the shortening in compression is proportional to the pressure (0.007% per day for 1 kgrn, per sq. crn,, 0.015% for 2 k grn, per sq. c m , ] provided that the pressure does not exceed about 4 kgrn, per sq. ern, at -5°C (23°F). At 5 kgrn, per sq. ern, the reduction in length is 0.11% (Haefeli). (b) Young's Modulus from Compression Tests between the Freezing Point and Zero Degrees. Progressive Loading. River ice, free from flaws, cracks, air bubbles or foreign material, was cut into cubes of 5 inches by 5 inches by 5 inches, or into prisms 5 inches by 5 inches by 10 inches. The loads were applied normally to the optical axis of the crystals. The initial load was 250 Ib., it was increased - 4 -

by 250 lb. at the end of either 5, 10, 20, 40, 80 and 160 seconds until the total load amounted to several thousand pounds. Several tests were carried out at each loading rate. Results are shown in the following table for the temperatures 28° F, 14°F and 3°F, for the intervals corresponding to an increase of 1,000 lb. of loading.

Young's Modulus E at various rates of loading (Compression at _2°, _8° and -16°C)

IncremJnts (40 lb. per 1st 2nd 3rd 4th 5th 6th sq. in.)

Young! s modulus in roo, 000 lb. per sq. in.

Temper- ature ° F 28 18 3 28 18 3 28 18 3 28 18 3 28 18 3 28 18 3 Rate of loading: 5 sec. 9.5 10.3 7.2 8. 7 9.3 5 7.7 8.3 3.7 6. 8 7. 3 2.8 5.3 6. 3 2 3. 1 4.3 10 sec. 8 5.8 4 2.8 2 20 sec. 6 11 3.6 7 2.3 5. 1 1.6 3.8 1 2. 8 2.2

I 80 sec. 7 4.3 1.1 3.2 2.7 2.3 2 160 sec. 5.3 2.8 1.8 1.3 1 1.9 320 sec. 5 2.8 1.5 1

The results show that the value of Youngt s modulus is progressively lower as the duration of loading increases, and as the actual load increases. Furthermore, the corresponding values of the modulus are higher at lower temperature. The difference tends to increase at each repetition. The values of Young! s modulus at 14 ° F for loadings five seconds apart differ but slightly from the values obtained at 3 ° F when the rate of loading is correspondingly decreased; thus the curve for a loading rate of 160 seconds at 14°F is a Irno s t the same as that for the loading rate of 320 seconds at 3°F. - 5 -

(c) Young's Modulus for Bending Stresses (Progressive Loading)

The beams tested were 3 inches wide by 2 inches deep, and the span was 41 inches. The load was applied in increments of one pound at each of two loading sections, 14 inches from the supports. The de• flection was read 5 seconds later and the load increased by one pound 1m other tests the loading intervals were 10 seconds, 20 or 40 seconds. One series of experiments was carried out at approximately 14° F, the other at 28° F.

Young! s Modulus (lb. per sq. in. )

Axis of c r ystals Axis of crystals horizontal vertical

Temperature

One pound loads added at intervals of

5 sec. 790, 000 844, 000 674, 000 80 8, 000 10 sec. 610,000 681, 000 751, 000 753, 000 20 sec. 450, 000 625, 000 661, 000 653, 000 40 sec. 355, 000 615, 000 441, 000 742, 000

In all the tests, the value of Youngt s modulus decreases in successive stages of loading, and with increased duration of loading at each stage. The value of the modulus is greater at the lower temperature. It is slightly greater when the crystals are vertical than when they are horizontal (Brown) with the optic axis parallel to the bar (average ratio 1. 15 and 1. 07); com• parison of the results is difficult, however, because the depth varied from beam to beam. (d) Young's Modulus for Decreasing Loads in Bending Tests on Beams of Ice Prepared from Frozen Snow

The bars used were about 250 rnrn, long, 15 rnrn, wide and 15 rrirri , deep. The optical axis, or the direction of freezing, was either parallel or perpendicular to one pair of side surfaces, and by merely turning the rod through 90° about its long axis, the behaviour in two different directions perpendicular to the optical axis could be studied; in one direction the crystal base planes would be parallel for single crystals, in the other orien• tation they were perpendicular to the direction of the force. In order to reduce deformations, no deflection was allowed to exceed 0.15 rnrri , at the centre of the beam. - 6 -

Each b earn was subjected to five or six cycles of loading and un loading before m eas urernents were started. Readings were then taken while the bar was unloaded in steps of about i kgrn, at a t irne , The re• rnova l of the load took about one second at each step.

Young's modulus in kgrn, per sq. ITlITl. at decreasing loads in bending near the freezing point

(i) Long axis of bar parallel to optical axis

1. 04 0.74 0.54 0.24 Load kgrn, kgrn, kgrn, kgrn. Average

First rod, first position 948.3 920.4 931. 0 953.5 938.3 second position 960.4 944.3 951. 7 924.8 945.3 Second rod, first position 934.3 935.5 940.4 958. 1 942. 1 second position 935.3 944.8 945.7 951. 7 944.4 Third rod. first position 971. 1 949.8 979.8 (1012.0) 978.1 second position 954.4 975.7 970.6 976.6 969.3

Average of these and other tests 957.6

(ii) Long axis of bar perpendicular to optic axis

First rod 1131 1134 1106 1116. 6 Second rod 1124 1111 1126 1121. 1

Average of these and other tests 1120.3

The rneas ur errierrts at decreasing loads give for stresses parallel to the optic axis a value of

= 95.760 kgm. per sq. ern. (13.6 x 10 5 lb. per sq. inv )

E = 112, 030 ｫｾｉｔｬＮ per sq. CITl. o (15.9 x 10 lb. per sq. in.)

= 1. 17

for stresses perpendicular to the optic axis. after repeated stressing and at ternper a.ture s a few degrees below freezing. - 7 -

(e) Young's Modulus from the Velocity of Sound in ice (Adiabatic Value). The difficulties that the progressive yielding of ice in all except the slightest stresses creates for the determination of Young" s modulus are avoided by methods depending on the velocity of sound or of high frequency vibrations, or impulses (Brockamp and Mothes; Boyle and Sproule). The testing forces are small and change very quickly. Using frequencies between 7 and 13 kilocycles per second and rods in which the optical axis is parallel to the greatest length, the results are as follows:

Young! s Modulus Temperature of lb. per sq. in. kgrn. per sq. ern. °c 6 14 1. 375 x 10 96, 700 - 10 - 22 1. 48 x 10 6 104, 000 - 30 - 31 1. 58 x 10 6 111, 000 - 35

Seismic methods applied to a glacier gave E = 71, 000 k grn, per sq. em. near the freezing point (Brockamp and Mothes).

(f) Miscellaneous Values for E Russian engineering articles use the following average values for Young's modulus in compression, bending, and tension:

30, 000 kgm. per sq. em. (Komarovskii) 30, 000 to 50, 000 kgm. per sq. em. according to the temperature (Bernstein).

(g) Rigidity of Ice and Poissont s Ratio The modulus of rigidity is determined from the twisting of cylinders about the long axis of figure, or from the propagation of high frequencies in rods of ice. The optic axis of the crystals may be parallel (N ) or perpen- dicular to the length of the cylinder (N 0 9 0).

Temperature, o C N N ton per sq. em. and per o 9 0 radian

about 0 27.2 29.4 Koch o 10 Weinberg - 5 17 Weinberg (both 1938) ＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭＭ｟ｾＭ

The propagation of sound gives a much larger value N = 91. 7, at temperatures between - SoC and - 15 e C for water frozen slowly in vertical - 8 -

brass tubes (Ewing, Crary, and Thorne). Seismic methods of wave propagation give N = 26, 100 kgm. per sq. ern. for ice contained in a glacier (Brockamp and Mothes). The ratio between Young! s modulus and the modulus of rigidity is 0.361 for glacier ice (Brockamp and Mothes), and 0.365 for high fre• quency sounds (Ewing et al ).

STRENGTH AT F AlLURE (a) General Features

In order to derive practical values for the strength in crushing, bending, tension, cutting and twisting, an attempt has been made to collect the results of all the tests made up to 1936 and to take the average. The result is as follows (B. P. Weinberg, 1936).

Number of tests on the strength of ice

Average strength Nurnbe r of tests kgrn, per sq. ern. in USSR in other countries before 1918 1918-1936 before 19181918-1936 Total

Crushing 43 75 279 72 32 458 Bending 17 345 346 44 66 801 Tension 11 10 63 27 5 105 Cutting 7 0 62 13 10 85 Torsion 4 9 0 0 0 9 Total 439 750 156 113 1458

Only about half of these measurements were made in a methodical fashion, the remainder were more or less casual observations so that the meaning of the average remains doubtful. Thus if, the group of readings obtained in crushing tests made under comparable conditions (281 determinations) and the corresponding bending tests (430 determinations) are arranged in ten groups of 28 tests (respectively 43 tests), in the order of increasing strength, and the average strength in each group is expressed in percentage of the sum of all the loadings, the result is as follows:

Distribution of Results Nurnbe r of group of tenths of total number 1 2 3 4 5 6 7 8 9 10

Average strength in 0/0 of total load used in crushing 45 57 64 79 88 99 III 123 139 195 in bending 47 62 83 86 94 102 113 126 135 162 - 9 -

These results show that readings lower than the arithmetic average are more frequent than readings greater than the average, in the ratio of about 3:2, and suggest that owing to the experimental difficulties, the number of measurements made under comparable conditions is not sufficiently great to lead to a satisfactory average.

(b) Crushing Strength of Ice To obtain characteristic compression fractures, the load must be applied rapidly, although without shocks, so that the ice has no opportunity to flow or to change. When the rate of loading is such that 40 lb. per sq. in. is added every other second, the crushing strength of 5 -inch cubes taken from the St. Lawrence river is as follows: Crushing strength Temperature OF lb. per sq. in. k grn, per sq. c rn, °C

28 300 21.1 2.2 14 693 48.7 - 10. 0 2 811 57 - 16. 7

There appears to be little difference in strength at failure whether the load be normal to the crystal basis or perpendicular to the optic axis (Brown). When the loading rate is only 8 lb. per sec. the cubes have time to change shape before they break. Tests on artificial ice, prepared either by placing distilled water or mixtures of powdered ice and water, in a refrigerator, were carried out in standard testing machines, using ice cubes of 7 c rn , side. The load was increased at the rate of 3 kgm. per sq. crn, per second (42.7 lb. per sq. in. per sec). At a temperature of - 8°C (18°F) the strength in com• pression in three series of tests was as follows (Romanowicz and Honigmann).

40.0 43.0 44. 1 k grn, per sq. c rn, at 8 0 C or 569 612 627 lb. per sq. in. at 18 0 F

The highest reading obtained was 54.4 kgm., the lowest 34 kgm. per sq. c rn,

When the five-inch cubes used for compression tests are quite clear, so that ordinary print can be easily read through them, the first outward signs of yielding at temperatures of 28 0 F to 30 0 F occur at loads from 100 to 200 lb. per sq. in. A slight noise is heard, and one or more spots of a slaky appearance develop in the block. These regions spread gradually through the block, and the ice is then no longer transparent.

At ternper a.tur e s between 14 0 F and 16° F and loading intervals of 5 sec. and 10 sec., the blocks remain clear even when the rnaxirnum load of 400 lb. per sq. in. is reached; only when the load is removed does - 10 - the ice become clouded faintly and fairly uniformly as a rule. At the slower rates of loading, however, the blocks become clouded. At 3°F the loads had to be added at intervals of 160 seconds to produce loss of transparency. That the temperature has a considerable influence upon the crush• ing strength is also shown by measurements by Witman and Shandr i.kov,

Relation between crushing strength and temperature

Temperature OF lb. per sq. in. k grn, per sq. crn, °C Ratios

23 220.5 15. 5 -5 1 14 253.2 17.8 -10 1. 20 5 354. 1 24.9 -15 1. 61 -4 394.0 27.7 -20 1. 80 -13 487.8 34.3 -25 2.20 -22 506.3 35. 6 -30 2.30 -31 583. 1 41 -35 2.65 -40 615.4 43.2 -40 2.80 -49 665.6 46.8 -45 3.02 -59 694. 1 48.8 -50 3. 15 -64 725.4 51.0 -55 3.30 -73 778.0 54.7 -60 3. 53

(c) Tensile Strength of Ic e Only a few determinations of the tensile strength of ice are avail• able (Romanowicz and Honigmann; Bernstein). At an average temperature of - 8 °C (18° F) the tensile strength, measured in a standard testing device for concrete on cylindrical pieces of artificial ice was as follows when the load was increased at the rate of O. 1 kgrn, per sq. ern, per sec. (or 1.42 lb. per sq. in. per sec. )

16. 1 18.3 17. 7 kgrn, per sq. em. 229 260 252 lb. per sq. in.

The highest reading in three series of measurements was 24.8 kgrn,, the lowest 14.8 kgm. per sq. crn, The tensile strength of ice is therefore less than half the crushing strength of ice at the same temperature and forms a limit that has to be considered in all cases of more complex stress distribution. Tests with natural icicles shaped into cylinders gave a tensile strength of

10.3 kgrn, per sq. crn, at - 2.4 °C (146.5 lb. per sq. in. at 28°F) 19.0 kgm. per sq. crn , at -6. 7°C (270 lb. per sq. in. at 20° F) - 11 -

The c r o s s - section of the test pieces measured 2 to 7 sq. crn,, the height 3.3 to 4.9 crn, The ice was coarse - grained (Haefeli).

(d) Strength of Ice in Bending The beams of St. Lawrence river ice used in the bending tests were loaded step by step until they broke. All the beams broke suddenly at or near the loading point. Tests were made with crystals either horizontal or vertical, either at 28°F or at l4°F (Brown).

Strength in bending (lb. per sq. in. ) (Modulus of rupture)

Axis of crystals Axis of crystals horizontal vertical Temperature 28° to 30 ° F Rate of loadmg: 5 sec. 178 232 170 191 10 sec. 173 217 170 216

20 sec. 134 228 243 ? 208 40 sec. 141 281 152 240

The average modulus of rupture for 21 beams tested at 28°F to 30°F was 171 lb. per sq. i.n , , which corresponds to a load of 150 lb. per sq. in. for a 5 -in. cube (Brown). At 14 ° F the modulus of rupture for 24 beams was 226 lb. per sq. in. The experiments reveal only a slight influence of the orientation of the crystals upon the breaking strength in bending although after 20 days beams, 54.5 inches long, allowed to bend under their own weight show a deflection of 9t inches at the centre or 17% of the span, when the crystals are vertical, and only 1 inch, or 2% of the span, when the crystals are hori• zontal.

Bending strengths have been measured at still lower temperatures for ice from the Arctic Ocean. The beams used measured 10 x 10 x 30 cm., the span used 20 crn, The load was applied as fast as possible either per• pendicular to the surface of freezing (or parallel to the optic axis), or per• pendicular to the axis (parallel to the base), or perpendicular to the sur• face nearest to the water (parallel to the optic axis). - 12 -

Rupture in Bending Tests (Nazarov) (Ice from Arctic Ocean)

Temperature Greatest Strength in kgm. per sq. em. Depth in ice °C of .L base 11 base ...l.... water base cover, c rn, -30.8 -13.4 40.0 20 -3 O. 8 -28 37.5 20 -30.8 39.0 33.5 25 -38 -36 35.0 50.0 40.0 15 -38 52.0 55.0 30 -38 29.0 30.0 5 - 1. 1 30 20.0 8 24 18 23 28

IMPACT STRENGTH OF ICE

(a) Strength in Sudden Loading When a mass moving at a velocity v hits one end of a light bar firmly held in place, or when the bar falls, the length 1 of the bar is changed until the total work done by the flying body against the tensions created in the solid is equal to the kinetic energy of the bar. The deflection d pr oduc ed in a bar of cross-section A is

2 v d = d +- d st g s t

where d = WI / AE is the elongation of the bar when the weight W is applied not only ｾｩ｜ｨｯｵｴ any initial speed, but is, moreover, increased very gradually from zero to its full value. It follows that even in the absence of initial speed the sudden application of the full load produces twice the deflection obtained with a load increasing so slowly that there is always equilibrium between the acting load and the resisting forces in the bar. Since the stresses set up in the bar are proportional to the elongations, or contractions, produced by the load, suddenly applied loads are more destructive than progressively increased loads. In the work done with ice from the St. Lawrence river, the most rapid rate at which progressive load could be applied to 5-inch cubes was 40 lb. per sq. in. in two seconds, but in a few other tests this load was applied within 1 2/5 seconds. The crushing strength is as follows: -13-

Crushing strength Ib/sq. in. 20 lb. per sq. in. 30 lb. per sq. in.

Temperature 0 F per sec. per sec. 28 300 343 14 693 500 2 811

The results are not conclusive.

(b) Shifting Loads

No measurements were carried out with loads shifted along a beam or an ice cover but practical experience is available on moving loads sustained by ice covers on lakes and rivers. Old ice that has been exposed to the sun and to air at temperatures not much colder than freezing becomes split into irregular pieces and has little sustaining power. New ice, 1 3/5 to 2 inch thick, will bear the weight of a man; when 3 3/5 to 4 in. thick, infantry marching in open formation; 4 in. of ice, a man on horseback; when 10 to 12 in. thick, an army; 15 in. ice supports railroad tracks and trains. Russian specifications are a thickness of 20 ern, ice for a railroad car of 15 tons (Moskatov).

(c) Impact Strength

With moving loads falling on ice the stresses created in ice can be increased at wilL If the velocity is large in comparison with the deflection that the weight would produce at rest, the tensile stresses in a bar of ice hit at one end by a weight W at a speed v is

2 2E Wv s = = Al 2g

Hence the stress produced by impact can be diminished not only by an increase in cross -sectional area as it would be under static conditions but also by an increase in the length (or thickness) of the bar. A similar formula is obtained for bending under the impact of a solid body. The stress is kept constant despite the increase in load when the thickness in the direction of the impact is increased in the same proportion. Some impact tests have been made with ice from the Arctic Ocean, shaped into cubes 10 x lOx 30 ern, (Nazarov). The falling body striking the ice was a pendulum bob with edges of about 5mm. radius. The length of the pen• dulum was one metre. - 14 -

Work for splitting ice in kgrn, rn,

Tem.perature IJ base 1 base II water base of °C

29.5 - 1. 5 5.9 4.3 3.7 25 - 4 5. 1 4.6 21 - 6 6. 1 6. 1 5. 5 3 - 16 to - 17 5.9 5.7 5.8

(1 kgrn . rn, = 7.233 foot-pounds. ) The necessary work increases less m.arked1y than expected with a decrease in tem.perature, probably on account of increasing salt content of the sam.ples. It is known that river ice splinters considerably when sawn at tem.peratures near to of. but is not difficult to saw at 30°F. PART II. STRUCTURAL PROPERTIES OF ICE -15-

EFFECT OF SALTS

The dependence of the properties of ice on the temperature is en• hanced by the presence of salts, because while water dissolves a large number of substances, at least up to a certain concentration, ice, being a crystal, is unable to receive into its lattice any substance that does not conform with its particular building plan according to the hexagonal system. No substance is known to be isomorphous with ice. When, there• fore, a sample of water containing salt is cooled until the freezing point is reached, pure ice crystals only are formed while the salt, despite its higher freezing point, remains in solution. The growth of the ice crystals continues, provided that the temperature is reduced in proportion, and the concentration of the solution increase s until a s tate is reached where salt and ice solidify at the same time as an intimate mixture of salt crys• tals and water crystals. The temperature at which this so-called eutectic mixture is formed is the lowest temperature at which the solution can ex• ist in the liquid form, and is the highest temperature at which salt crys• tals and ice can exist indefinitely side by side. The eutectic solution of potassium chloride and ice forms at -11. 1°C and represents a concentration of 24. 6 gm. of potassium chloride in 100 grn. of water. With ordinary salt the eutectic mixture contains 26.3 gm. salt in 100 grn, of solution, but the salt deposited is a hydrate, NaC 1. 2H 0. The eutectic temperature is -21.2°C (-6.20F). 2

Composition of the Salt of Sea-Water

grn, per kgrn , (mills by weight) Chlorine

NaCl 26.9 16.33 MgC1 3.2 2.38 2 MgS0 2.2 4 CaSO 1.4 KCl 4 0.6 0.28 Rest o. 1 34.4 grn, per kgm. of 18.99 sea-water The concentrations of salts in sea-water are such that the eutectic composition will never be reached in the open ocean even after a thick cover of ice has been formed, and it is hence well nigh impossible by any cold occurring in nature to solidify sea-water. If freezing proceeds with great speed, then, of course, the salt contained in sea or river water has not necessarily time to escape into -16-

the remammg liquid; it may become trapped between the ice crystals. Unless it forms an uninterrupted jacket around the ice crystals, it is gradually squeezed toward the boundary by the arrival of neighbouring ice molecules attaching themselves to their likes. Similar effects are obtained in melts of metals, but the mobility of the molecules is very much less than that of ice molecules because in every day use metals are far below their melting point.

Lowering of the Melting Point by Sea Salts (gm. salt per kgm. sea-water, that is, mills by weight)

gm. gm. grn , per per per kgm. t = °C kgrn. °C gm °C kgm. °C

1 -0.055 11 -0.587 21 -1. 129 31 -1. 683 2 -0.108 12 - O. 640 22 -1. 184 32 -1.740 3 -0.161 13 -0.694 23 -1. 239 33 -1.797 4 -0.214 14 - O. 748 24 -1. 294 34 -1. 853 5 -0.267 15 - O. 802 25 -1. 349 35 -1. 910 6 .0.320 16 -o. 856 26 -1. 405 36 -1.967 7 -0.373 17 -0.910 27 -1.460 37 -2.024 8 -0.427 18 - 0.965 28 -1. 516 38 -2.081 9 -0.480 19 -1. 019 29 -1.572 39 -2.138 10 -0.534 20 -1. 074 30 -1. 672 40 -2. 196

Note:

Sea-water averages about 35 gm. of salts per kgrn, The average temperature of the surface layers of the oceans is -1. 7°C at 80 0 N and S. The first signs of freezing of ordinary sea-water are observed at 28.7 ° F (-1. 8°C). Detailed investigations have shown that ordinarily the ice from sea-water contains some salt, about 4 or 5 parts per 1, 000 parts of ice in place of the 35 parts of salt originally contained in sea-water. In newly formed sea-ice the salt is uniformly distributed throughout the mass, en• veloping the crystal grains as far as can be ascertained, but as the ice ages, there is a migration of the salt from the interior to the surface, and the salt content of the ice in the Arctic Ocean is taken as an indirect measure of its age. It may decrease from 4 or 5 parts per thousand in young ice to only 1 or 2 parts per 1, 000 in ice two months old, and the ap• proach of s urnrne r finds a great part of the original salt squeezed out and appearing on the upper surfaces, where it is removed by wind and water. The polar cap ice covering the ocean from latitude 881 northwards to the -17 -

pole, six to ten feet thick, is several years old and free from salts. "When ice forms in the fall, it is as salty as the water out of which it is made, and if you take a chunk of it and melt it you get brine unfit for the ordinary uses of water. The ice remains salty all winter, but the following spring, as soon as the warm weather comes, it begins to freshen, and even though the cake be of considerable size it will freshen enough for use in tea-making or other cooking by the end of summer. But the lagoon ice which has never been over six feet thick to begin with, thins down to a few inches by July and cakes of it are perfectly fresh by that time. " (Stefansson, My Life with the Eskimo p. 115). Salts in water are responsible for the brittleness in artificial ice and for the tendency of artificial ice to crack. Different sections of a country have their own particular type of water, and the ice made from certain kinds of water will crack sooner or later. That is, if a cake of apparently clear and good ice is taken from the form in which it was frozen and left lying for five or ten minutes, it may be found to have cracked into several large pieces. Cracking can be caused by stresses arising in a block of ice as a result of different expansion rates when different parts contain variable amounts of impurities.

A block of artificial ice taken f r orn a can in which it was frozen for eight hours at -10°C to -15°C consists usually of three separate zones, namely, a strikingly clear crust around the top where the water froze slowly; it is traversed by flat bubbles of air. This ice surrounds a conical plug of ice crumbs with many air bubbles, the last portion to freeze. Below it is the main part of the block frozen first in contact with the walls cooled by the brine; it con- sists of plates perpendicular to the walls, the only impurities are air bubbles that appear where the growing ice crystals meet in the interior of the block In this zone the impurities may amount to 0.02%, in the clear crust to 0.09%, and in the plug to 0.11% when the water supply contains 0.09% impurities. With one per cent of rocksalt added to the water, the main part of the block shows the horizontal crystal plates rnor e distinctly; weak ice oc• cupies the entire centre of the block, beginning with slush at the top. The concentration of the salt is 0.2% in the outer portion, 1. 7% in the core, and 3. 3% in the liquid portion. This portion is not frozen after 24 hour s of cooling. (G. 'I'arnrrian and K. L. Dreyer, Naturwiss. 22:613-614,1934). The aspect of the block is slightly different when salts are present that are rrior e soluble the lower the temperature. These impurities are caught in the portions of the water which freeze first, the lower corners of the can and the edges. They tend to forrn a white shell around the block. Whatever the nature of the salt, when the block is allowed to warm up, the less pure portions expand at a rate that is different from that of pure ice, and the stresses may be sufficient to crack the ice. The solution -18-

trapped between the crystal plates has moreover, a lower melting point and forms planes along which the ice is easily split. When ice contain• ing salts is allowed to warm up from -20 ° C, it begins to contract at temperatures far below the melting point whereas pure ice expands until it has reached the melting point. When ice forms at the surface of the sea, the temperature gradients are more uniform than when an artificial block of ice is produced, and no cracking occurs. On the contrary, salt-water ice when it warms up never disintegrates into separate crystals as does fresh-water ice' it is tough and reliable. Whilst fresh-water ice cracks like a window pane hit by a stone, salt-water ice bends before breaking and gives warning that it is not strong enough. According to V. Stefansson, in the fall an inch and a half of salt-water ice is preferable to two inches and a half of fresh-water ice. THE PRODUCTION OF LARGE SINGLE CRYSTALS

Blocks of artificial ice sometimes yield fragments which indicate by their behaviour in polarized light and in X- ray diffraction that they are single crystals. These fragments are lO em. in length and 1 to 2 sq. em. in cross-section. Such a piece is suitable as a seed for the production of large crystals. It is given two opposite plane-parallel surfaces' one of the faces is frozen to the outside of the bottom of a metal can containing a freez• ing mixture at about -10°C., and the opposite face is allowed to dip just below the surface of a pool of distilled water, boiled and cooled nearly to zero 0° as rapidly as possible. The water is kept at that temperature by a jacket of melting ice. Crystallization proceeds from the seed into the water at the rate of a few mrn, per hour. Single crystals with dimensions of the order of lO em. are readily produced. If a clear and flawless single crystal of ice is exposed to the heat from the sun or an arc focused on a small region of its interior, a cavity nearly filled with water forms. The ice-flower appearing in this cavity indicates the orientation of the crystal axis (Adams and Lewis). That an ice cover consists of separate large crystals is best seen when fresh-water ice thaws in the spring in places where it is not covered by smoke and soot. In the spring freshets the northern rivers leave huge blocks of ice stranded on the bottom lands. Stefansson reports how one morning he passed one of these blocks deposited by the Coppermine River and found it quite as high as himself. In the evening, when he returned over the same ground, he was astonished to find the boulder of ice missing. A little search showed a flattened heap of crystals, some of them a foot or more in length. "The whole cake had divided into separate crystals and all of a sudden the forces of cohesion had given way and the whole thing had settled down into a loose pile." Later on the explorer used to walk up to -19-

these stranded bowlders of ice and give them a smart blow with a stick. It happened now and then that one of them would crumble at a touch into exactly such a heap. When entering upon the surface ice of the first of the lakes between Darnley Bay and Langton Bay (13 June 1911), the ice was breaking up into needles or crystals in the manner of the ice boulders. A sharp pointed pole could be jabbed into the ice and forced between the crystals down to the water below, although the ice was at least three feet thick (Stefansson, My Life with the Eskimo p. 322). Apparently the crystal faces though invisible, reflect light and heat to and fro; they thus favour the absorption of the radiation near the walls and the separation into pri srns and needles. To d ernonstra te the crystalline structure of ice, Tyndall passed a b e arn of light through it. Hexagonal cavities are produced in the ice, the process of crystallization being as it were reversed. As the action of the b e arn proceeds, each cell becomes filled with the water which it occupied as ice. The centre of each unit is occupied by a bubble of water vapour. The cells lie at right angles to the principal axes of the ice crys• tals and parallel to the original freezing surface, the surface of easiest cleavage.

HEAT CONDUCTIVITY

The heat conductivity of ice is difficult to measure because when there is a flow of heat between a block of ice and a rne tal plate frozen to it, there is always a discontinuity in the ternpera ture at the junction. It is rnos t mar ked at the lowest temperatures. The rno s t recent measure• rnents give the following values.

Heat Conductivity

Milliwatt Calories B. t, u, I per in. t in °C per crn.v C per CIn. sq. ft. h.oF of sec °C. -3 6 0 22.4 5.354 x 10_ 15.5 x 10 32 3 6 -10 23.2 5.545x10_ 16. 1 x 10 14 3 -20 24.3 5.808 x 10_ -4 3 -30 25.5 6.095 x 10_ -22 3 -40 26.6 6.357 x 10-3 -40 -50 27.8 6.644 x 10_ -58 3 -60 29. 1 6.955 x 10_ -76 3 -70 30.5 7.290x10 -99 -6 6 (one rrriIl.iwatt per CIn. °C = 239 x 10 cal. em. sec DC. = 0.693 x 10 B. t , u , per in. sq. ft. h. ° F. )

The theerna.l diffusivity, k, per unit density and per unit specific heat is 0.011 CIn. per sec. when the ternper a.ture is between 0 and -30°C.

The ther mal conductivity of snow depends on the density p of snow (0. 11 to O. 5); for very fluffy snow the density is O. 11 that of water and the -20-

-3 heat conductivity 0.153 x 10 calorie per em. sec. °C., increasing with the density according to the formula, k = 69.3 + 69.3 (100 density) microcal per em. sec. DC. The heat conductivity of snow is therefore from 30 to 3 times smaller than that of ice, the diffusivity

2.0 + O.lp + 10.3p2 D = sq em. per sec. 1000 is two to three times smaller. It is known that Eskimo occupy their igloos only about 3 weeks, for the heat inside melts the snow walls and as they cool off during the night, they turn gradually to ice and the house grows colder and colder. The arctic snowfrom which igloos are built consists of tiny needles of ice, it is quite porous but nevertheless not a loose mass.

ULTIMATE STRENGTH OF ICE IN SHEARING Tests were carried out on rectangular specimens of artificial ice 3 in. by 3 in. in cross-section. The average value of the shearing strength in the direction parallel to the basal planes was 114 lb. per sq. in. and in the direction parallel to the crystal walls 98 lb. per sq. in. The maximum value read was 353 lb. per sq. in. parallel to the walls of the crystal, at 30°F., and the minimum value 68 lbs. per sq. in. parallel to the basal plane at -12 ° F. At temperatures below zero, greater values were obtained when the load was applied rapidly. At temperatures above 20 0 F (- 6.7 0 C) rapid application of the load was necessary to obtain reproducible results. The strength in shear of artificial ice is about 80% of that of river ice (Finlayson). Some older measurements reported from Russia (by Weinberg, 1936) give 57 lb. per sq. in. for the shearing strength of ice. Whatever the correct value, there is no doubt that where the necessary force is con• venient to apply, ice is much more easily broken by shearing than by pressure. The values obtained for the strength in shearing are comparable with the figures deduced from punching. There seems to be a minimum load below which punching does not occur; in one case a load of 5 kgm. (71. 15 lb. ) produced no observable effect in 24 hours, but when the load was increased to 7 kgm. (99.6 lb), the deformation was rapid. Temper• ature changes between -3°C to -16°C do not alter the results (Miigg e}. -21-

INTERNAL FRICTION (VISCOSITY) OF ICE

10 The values found for tg.e coefficient of viscosity of ice vary from 10 grn, per crn, sec. to 10 grn, per crn, sec. for glacier ice whereas the corresponding value for water is known quite accurately, O. 018 at 0 0 C. and 0.015 at 5°C. It is claimed that where the flow of glaciers was most accurately studied and measured (Hintereisferner, Pasterze in Austria) 14 the most reliable measurements gave value 1. 0 10 gm. per sec. ern. + 10% for the internal friction of ice.

EXPERIMENTAL WORK ON THE ADHESION OF ICE

It was observed at an early date that if ice is firmly frozen to concrete it will break or crush before it can be detached from the con• crete by p r e s s ure, shear in tension. An article by G. G. Bell gives the following results on the strength of adhesion:

Temp. 0 F Size ice, Unit load at Unit adhesion inch failure, lb to concrete, lb 30 2 x 3 370 195 30 2 x 2 504 228 32 3 x 3 395 158 32 3 x 3 250 116 30 3 x 3 420 185

The Adhesives Research Committee of the Department of Scientific and Industrial Research mentions in its Second Report (p. 41, 1922) experi• ments with lubricants and other substances between metal, glass and fused silica surfaces. They showed that ice between fused silica surfaces gives a very strong joint. When a piece of metal is submerged in water and the water freezes, the ice adheres strongly to the metal surface, an effect which illustrates the molecular attraction between water and metal. The force necessary to separate the ice from the metal surface may be taken as a measure of the strength of adhesion; referred to unit area, it will be designated by P, the extraction or breakaway tension, on the assumption that the forces of cohesion of the ice itself are sufficiently large. If a weak plane S is present in the ice quite close and parallel to the metal surface S the metal piece may become loose before the extrac• tion tension that corresponds to the forces of adhesion has been reached. The values of P may therefore scatter a great deal, depending upon the perfection of the crystals. Other disturbing influences cause a reduction in P, and the maximum values as well as the average values deserve consideration when the experiment is repeated. -22 -

Two kinds of stress can produce breakaway; either a force is applied that is parallel to the surface of separation of the metal and ice, or a force that is perpendicular to the surface of separation. In this latter case the measured value must be decreased by about 1 kgm. per sq. em. in order to take atmospheric pressure into account. Three methods were used. (1) Extraction of strips and wires, frozen into the ice. When S is the total area to which ice adheres, and K the tangential force that pulls the metal from the grip of the ice. P = K/S (2) The wrenching free of cylindrical rods of r adius vr and immersed length 1. At the upper end each rod is provided with a short lever arm of Iength a , A wire attached to the end of the arm is loaded with weights until the rod starts to turn in the ice. Then Ka 1 Ka P = r S = 2 2n r 1 The force relates to a shearing action as in the first method. (3) Removal of plates frozen to the surface of ice, by means of a perpendicular force K so that P = K-l S The force K was m.eas ured by a dynamometer. The surfaces were cleaned with care, first sandpapered, then washed with alcohol and with distilled water. Caustic soda was also used at times. If the surfaces were not clean, (e. g. when, for instance oxidized brass rods were used) the values obtained were lower by about 12%· Results For method (1) brass strips 1.5 em.• 0.85, or 0.65 em. wide and 2..5 to 3.5 em. long were used. The temperature was about _12 0 C (10.4°F). The measurements gave for s = 8.3 5.5 3.4 sq. em. P = 4 5.5 6.9 kgm. per sq. em. or (80 110 180 lb. per sq. foot) The decrease in the value of P when the surface area S is made larger is caused, apparently, by defect, at the surface of separation or in the ice. When the values were extrapolated to S = 0, in order to eliminate the influence of local defects, P = 12 kg. per sq. em. (about 240 lb. per sq. f t,.}, Brass wires gave similar high values:

Diameter S P 0.9 m.m O. 87 sq. em. 10.6 kgm. per sq. em. 0.4 mrn, 0.39 sq. em. 12.6 kgrn, per sq. em. -23-

Method (2) was used with brass rods 2 to 3 rnrn, in diameter and 2 to 3 em. length. The temperature was about -7 °C. (19.4 ° F). Four pieces of brass and four pieces of another metal were used in each test in order to get a direct comparison between different metals. The re• sults are shown in the table. Average P Pmax Ratio Number of tests Copper 17. 6 23.9 1. 25 7 Brass 6 14. 1 1 6

Zinc 25.0 34.5 1. 33 12 Brass 18. 8 29.8 1 11

Aluminum 24. 1 27.7 1.38 8 Brass 17.4 22.0 1 8

Iron 29.6 37.6 1.5 8 Brass 19.9 28.4 1 8 According to the ratio obtained for P (in kgm, per sq. em. the ad- hesion of ice to metals increases in the order.

Brass Copper Zinc Aluminum Iron 1 1. 25 1. 33 1. 38 1.5

The values obtained for brass, by method (2) (Temperature _7 0 C), exceed the values obtained by method (l){temperature - 12°C),; the reason must be sought in the brittleness of ice which becomes very pronounced below - 10° C. Method (3) proved to give consistent results provided that the pieces of metal be held in place during the formation of ice and that they do not prevent the escape of air bubbles set free during freezing. The tests were carried out as follows. In the vertical front wall of a zinc box some holes were provided into which small discs of metal, the size of coins, were placed and fastened with paraffin. Each disc was provided with a hook to which the force was applied. After the extraction the discs were sometimes quite smooth and dry; in some instances splinters of ice were seen to ad• here to the surface. The temperature was -7°C (19.4°F).

Diameter Average P Pmax 2.2 em. 7.9 11.5 0.7 II 18 26 [kgrn, per sq. em. ) Here again the smaller areas give the higher values. Tests with sulphur showed that near the melting point, 114°C, the force of adhesion is practically zero and increases to a limit of 55 kgm. per sq. ern. near 20° or 30°C. The values measured immediately after -24-

solidification were often quite different from those measured 24 hours later. (A. Sellerio). More recent qualitative and quantitative determinations of the force required to remove ice from various surfaces are reported by the National Advisory Council for Aeronautics. The surfaces were maintained at temperatures below 32 ° F. by placing them in a box containing sufficient solid carbon dioxide to hold the inside at the desired temperature. A window was provided for visual observation. Blocks 1 inch square were made of material for which the adhesion to ice had to be measured. Two blocks were held in position 1/8 inch apart by means of adhesive tape. The space between them was filled with water, the water allowed to freeze, and the hook on one metal block fastened to the bottom of the cold box. The shearing force required to separate the blocks was measured by means of a hydraulic ram. It was found that with ice adhering to a solid surface, the rupture occurs in the ice at a loading of about 140 lb. per sq. in. lee will adhere to any surface tried thus far with a force greater than the cohesive forces within the ice. For Brass Duralumin Steel At 21°F 25°F 21 of Failure occurred at 130 132 139 lb. per sq. in. If the temperature of the ice was brought considerably below 0 ° F the ice tended to crumble. Ice will not adhere to a surface when there is a distinct liquid layer between the ice and the solid surface. If such a liquid interface is formed the force required to remove the ice is little more than the resistance or pressure of the air tending to hold the ice to the surface, too low to be measured with the instruments used. When ice was adhering to a greasy surface, failure occurred be• tween the ice and the grease at a loading equal to, or little greater than, atmospher-ic pressure. For a viscous liquid the force measured was 15 lb. per sq. inch, for micarta with a greasy surface 53 lb. per sq. in. In all the tests the results scatter a great deaL (A. M. Rothrock and R. F. Selden) A few recent tests by Roy W. Carlson at the Massachusetts In• stitute of Technology gave a figure of approximately 115 lb. per sq. in. for the strength of the bond holding t inch plain steel rods in 4 in. cubes at temperatures between 4°F and gOF. Only two tests were made (Ice and Refrigeration 100: 4, 1940)*

ICE FLOES AS LANDING FIELDS FOR AIRCRAFT The polar cap-ice which throughout the year covers the deep central major portions of the north polar basin, is distinguished by great solidity, the large size of its fields, and the thickness of its rafted hummocks * This reference cannot be verified. -25-

of ice blocks. It occupies 70 per cent of the polar basin, about 2,000,000 square miles; its margin follows roughly the I, 000 rn, depth of the ocean. The movement of the cap ice is not completely known. There is undoubtedly a movement from east to west from Point Barrow around the Siberian continental shelf, and finally out into the Greenland Sea. The wind is, no doubt, a major factor in keeping the polar ice in motion. Winds and currents may shove fields and floes in the polar sea one above the other to heights of 100 or 130 ft. and to depths of 330 to 700 ft. Large areas of open water, known as polynyas, remain in the polar cap-ice, in particular a belt several hundred miles long north of the New Siberian Islands, and Peary's Big Lead north of Grant Land and Greenland. Open places are encountered even in winter. On March 14, 1938, a wide lead was observed between lat. 81 ° and 84°N. and longitude 122 ° to 127 ° 150 miles long and varying from 20 to 500 yards in width (Sir H. Wilkins). Ice that breaks away from the polar cap or from the fast ice along the shores invades the North Atlantic along the eastern coast of Greenland; another stream of ice, or pack ice, moves along the eastern side of North America from the Arctic Island to the Grand Bank. Both streams are augmented by icebergs broken away from the glaciers of Greenland, Spits• bergen, Nansen Land, Northern Land, and Bennett Island. The remarkable sustaining power of large ice floes in quiet water was pointed out and explained by H. Hertz as early as 1884. It remained for the explorer R. Amundsen to take advantage of this property. When the Schooner "Maud" was caught in the ice between the New Siberia Islands and Wrangel Island in June 1923, a Curtis single-engined plane equipped with skiis was lowered on the ice. The first two flights from the ice floe were successful. On starting for the third flight, the engine stalled and the lower wing of the aircraft crashed into a pile of ice. During Amundsen's 1925 explorations between Spitsbergen and the North Pole, two Dornier- Wal flying boats took off from snow covered ice and landed on open water (lat. 87°north, Longr l Ovwe.st}, Much valuable experience regarding flying conditions in the Arctic was gained on this expedition and the possibility that aircraft could take off from ice floes was clearly demonstrated. Soviet pilots followed with a series of similar attempts. "The first place in this connection certainly belongs to the polar pilot M. S. Babushkin, killed all too early in a plane crash at Moscow in 1937; he made a large number of landings and take-offs on floating ice, in aircraft of different types, some of them provided with floats, others with skiis. The first one of his flights was carried out as early as 1926 during a search for the dwelling -places of seals around the White Sea. It is necessary to note that at the time no theoretical calculations existed and each pilot had to fear and risk everything each t irne he was forced to land on an ice floe, or to take off from floating ice. Therefore even when such an -26-

aviator would have done nothing but bring horne his plane in safety, he had accomplished a heroic deed. This particular skill reached its perfection in 1928 during the mercy flights (June and July) to the wreck of the dirigible ItaHa, 20 or 30 miles north east of the most northeasterly Spitsbergen Islands. Under difficult conditions, Babushkin landed on and took off from ice floes on no less than fifteen occasions, in a sing1e• engine metal monoplane YU -13. Neither before nor afterwards was such a number of landings in Arctic aviation made by a single pilot on landing places measuring approximately 200 x 550 sq. ft. A large amount of experienc e on drifting floes of pack ice was gathered in April 1934 during the rescue of the stranded passengers of the steamer "CheLius k in!' which was crushed by jamming ice and sank on 13 February, in the Chikehee Sea north of Kamtchaka. The "Cheliuskin" was an ice-breaking freighter, constructed during 1933 in the dockyards of Burmeister and Wesh, Denmark. The vessel of steel, was 307 ft. long, 55 ft. wide, with a displacement of 3,600 tons. In the last two hours during which the vessel was afloat, the passengers, numbering 104 (including 10 women and 2 children) were able to disembark upon the sur• rounding ice floe, to unload tents, provisions, and building materials intended for Wrangel Island. Within a week a hut sheltering 50 people had been built; the others continued to live in heated tents. An amphibian aeroplane Sh-2, which had served for ice surveys during the expedition, was also unloaded. All around the ice floe were numerous channels of open water; the heaped-up ice blocks reached heights of 60 feet but three miles from the encampment there was an area of smooth ice suitable for the landing of aeroplanes and the Sh-2 was removed to this place, because the ice on the flow began to show cracks. Rescue expeditions were organized on all sides. The pilots Kukanov, Kopnin, and Liapidevsky in U elen and at Cape Severny were instructed to fly at the first sign of favourable weather. Three aeroplanes were avail• able, the T-Z at Cape Severny, and the ANT-4 and a light aeroplane U -2 in Uelen. On 4 Mar ch, Liapidevsky landed at the ice aerodrome, took on board the women and children, and brought them safely to UeIen, He left fuel for the Sh-2 in the camp so that the pilot, M. S. Babushkin, would be able to fly it in an emergency. -27 -

G. A. Ushakov, Vice-Director of the Chief Adrrrirris tra tion of the Northern Sea Route, and the pilots Levanevsky and Stepnev, were sent to Arne r ica to undertake flights f r orn Alaska. They bought two passenger planes f r orn the Pacific -Alaska Airways Corporation, and took off f r orn NOITle. Levarievskyt s plane was forced down by icing near Cape Onrnan and was wrecked in the landing, but on 3 April the second Arn.er ican aeroplane, piloted by Stepnev arrived at Uelen. On 7 April the weather p errni.tted to fly to the caITlp and to take five rnen to the shore. On the s arrie day one of seven aeroplanes R-5, which had been brought by the s t earne r "Srriol ens k " f r orn Vladivostok to Oliutorsk arrived at Uelen. Fair visibility allowed the pilots, Karnarrin and Molokov to fly to the caITlp on April 10 followed by Stepnevt s plane. Four landings were rnada on the ice, and 22 people r errioved, On that day the caITlp itself was experiencing the strongest pressure, a high ice rampart fell upon the c arnp, crashed the hut and pushed it into the water; the aerodrome was entirely broken. On the follow• ing day seven landings were carried out and 22 rnen were taken off by Molokov and Karnariin, assisted by Doronin and Vodiapanov who had arrived with another of the R-5 planes. Only six rneri r erria.ined on the ice, arnorig theITl the wireless operator Krenke l and the captain of the vessel; they were rescued on 13 April, after a stay of two months on the ice floe. A dozen landings had been rna.de on the ice floes without an accident. The experience gained in this rescue operation, COITl• bined with the experience of the polar pilots A. D. Alexeyev, M. 1. Koslov and others enabled the Soviet Union to undertake an ex• pedition to the North Pole, to land on the polar ice with four four• engined aeroplanes (with Vodiopianov and Babushkin in the N-170, Molokov in the N-17l, Alexeyev in N-l72 and Mazurnk in N-169), to establish the polar research station on a drifting ice floe, and as a lasting conquest of the North Pole, to unveil the secret of the rnovernerrt and the behaviour of the ice floes in the heart of the Arctic. II (Moskatov) The four-engined Soviet aeroplanes that landed on skis near the Pole had each brought 21- tons of various supplies for the party of four that was to carry out scientific observations for nine rnonths on the ice. All the planes landed safely on skis after their 500 -rrril e trip f r om Rudolph Island to the North Pole. The landing field was an ice floe 10 ft. thick, 21- rn.il.e s long by Ii rrril e wide; in May it was quite level and stable but after a m onth a wide fissure was discovered under one of the tents. By 1 July, pools of water had formed everywhere under the snow. To• wards the end of July ice walls and pressure ridges had begun to appear on the floe, one of the ice walls was 30 feet high and nearly 330 feet long. The water on the floe became so deep that it would have been possible to sail a ship across the floe. At the beginning of October the floe had 0 drifted to latitude 85 , but the increasingly cold weather and the surround• ing floes protected the floe f r orn total destruction by the a u turrin gales. -28-

At the end of the year the floe measured 98 x 164 sq. ft. On 19 February, 1938, the four members of the party were removed from the floe by ice breakers, just after an aeroplane from the rescue ship had landed on the landing field Ii miles from the encampment. The dwindling ice floe had drifted 1560 miles from a point within 35 miles of the North Pole towards the coast of Greenland, at 71 0 lat. N. Outstanding ac hievements during 1940 were a flight from Tixie Bay (Lonely Island) to the "Pole of Inaccessibility" (lat. 84 0 N, long.160 0W), and a flight from Dickson Island to a point lat. 82 "N, long. 83 o E. The most recent landings on the pack occurred in March and April 1941 on a flight from Wrangel Island. Ivan Cherevichni and four others flew from Moscow and made a descent on the pack in lat. 81 °2f N., long. 180 °E. The next flight was to lat. 78 "N, , long. 176 0 40! E., and the third landing was atlat. 78°N., long. l700E. The ocean depths were found to be between 6, 000 and 12, 000 ft.

PROPERTIES OF SEA ICE (Translated from the article: Contribution to the study of the properties of sea ice, by V. S. Nazarov. Transactions of the Arctic Institute 110: 101-108, 1938). In 1935, the Polar Ice Laboratory was organized on Lonely Island (Kara Sea). In its first year it studied the impact strength of sea ice and the strength in repeated bending. The results were as follows: 1. The strength of ice depends on its structure and on the arrangement of the crystals. The structure of ice depends on the conditions during its formation and the composition of the water from which it is obtained. 2. The ice that forms on the sea early in winter, or in the middle of winter, when the temperature is just suf• ficiently low, is weaker than the ice of the cover that grows slowly dur- ing the winter. For reasons to be indicated, the change in strength is about 10 per cent or 12 per cent. 3. This condition is due to the fact that the first ice crystals floating in the water congeal to a mass with ir• regular orientation of the crystals, but that in the second ins tanc e, when ice grows from an existing ice cover, the crystals form an orderly arrangement and produce a strong mass of ice. Sea ice forrned in stormy weather, or in strong currents under the snow cover, must, for the same reason, be weaker than the ice formed in calm weather and in calm water. 4. The strength of the ice depends on its temperature, it increases with decreasing temperature. 5. An increase in the salt concentration re• duces the strength of ice at one and the same temperature. 6. Fresh water ice has greater impact strength than sea ice, but the tests on fresh water ice are rendered difficult by the large quantity of splinters. 7. Tests show that between -2 ° C and - 8 ° C (28 i o F to 17io F.) the force required for breaking an ice cover by applying it to the plane surface in contact with the atmosphere, in the manner that ice is attacked by an ice breaker, -29-

must be about 15% larger than the force applied for this purpos e to the lower side of the ice, in contact with the water, and about 5% greater than the force necessary applied in a direction parallel to the flat sur• face, the wayan ice breaker would cut the ice. 8. The results indicate that for bringing a ship through thin ice it is economical to use an ice breaker with a vertical bow, and for breaking harbour ice an ice breaker with an oblique bow. For work in ice of average strength, where the ship may become ice - bound, the best type of ship is the ice - breaker with a hull that can free itself by pressing against the ice cover. (With an average uncertainty of the results equal to 10% or 15%. it is impossible to attach real meaning to the author's distinction in (7) and (8),and still less to issue recommendations on this basis for ice breakers with verti• cal bows, unless the preference is proved by other considerations. To comply with the author's wish, the text has been left unchanged, but the Editors state that they consider the question not settled).

ICE IN EXCAVATION OF SHAFTS AND TUNNELS

The freezing of water -logged soil in order to render pos sible the excavation of pits, tunnels and shafts was fir s t applied in 1862. When encountering ground water during the sinking of an Artesian well near London, a cooling pipe in the shape of a large coil traversed by brine, was sunk into the quicksand. The method was studied and used on a much larger scale twenty years later by F. H. Poetzsch for the sinking of colliery shafts in German Mines and by Captain Lindmark, who was engaged in the construction of a tunnel for foot passengers through a hill in an inhabited part of Stockholm. The freezing process is most useful in sinking shafts through alluvial ground where the amount of water to be dealt with is too great to be handled by pumping and the pressures are too high to be balanced by compressed air. In the more than fifty years that it has been in use, the technique has emerged from the experimental stage and experience has led to the development of methods suitable for general use. In sinking a shaft by this process, a series of pipes arranged in a circle is first put down into the ground outside the boundary of the shaft to be dug. The freezing pipes consist of two parts; first, heavy weldle s s steel tubes closed at the bottom, and placed inside bore-holes drilled by ordinary methods; secondly, smaller pipes open at the bottom inserted into the wider pipes. Cold brine is circulated through the inner pipes and up in the annular space between the two pipes. In this way a cylinder of frozen ground is gradually forming around the pipes. The increase in diameter is relatively quick at first, but becomes slower as the size increases, until finally a condition of equilibrium is reached and the ice cylinder ceases to grow. But if a number of pipes are put down in a circle outside the proposed shaft, provided that they are not spaced too far apart, the ice cylinders will eventually touch one another, and a solid ice wall will sur• round the site of the shaft. -30-

It is found that soft ground, such as quicksand can, when frozen, be safely relied upon to withstand a compression of 150 lb. per square inch. At the bottom the ice wall must extend to firm impermeable ground.

In practice it is found that under average conditions, the most economical spacing for the pipes is about 3 ft. for a wall 3 ft. thick to be obtained in a reasonably short time. In larger shafts more than one ring of pipes suitably staggered may be necessary. Special precautions must then be taken to prevent pockets of ground to be left unfrozen, which when cooled later might cause internal stresses in the ice wall. Various instruments have been devised and used with succ es s for sur• veying bore-holes and keeping pipes vertical even when the length ex• ceeds 200 ft. The ideal to be aimed at is to freeze the ice wall only and leave an unfrozen core of soft material in the centre. Rock drills and explosives may be required for the removal of frozen ground. In a small shaft, 15 ft. or less in diameter, it is of course impossible to prevent the appearance of a frozen core at depth when the freezing process extends over a few weeks. In 1932 the shafts required for the intake and discharge openings of the condensing water tunnels at the Swansea power station had to be excavated through very soft mud, running sand, open gravel and other water -bearing deposits. It became necessary to choose between driving the tunnels at a shallow depth in unstable ground to enable compressed air to be employed or sinking the shafts by freezing to a depth at least 170 ft. that would allow the tunnels to be constructed in free air under an ample cover of rock. Fears of subsequent settlement and assurance by the most experienced local colliery experts that the freezing process would work led to the adoption of the deep level scheme. The advice of the Foraky Company of Brussels was secured for planning the freezing proces s , The circle on which the pipes around the shaft at Swansea were inserted was 22 ft. in diameter, 3 ft. outside the line of excavation. Twenty-four pipes were provided, spaced 2 ft. lOt in. apart. Under the contract they must not deviate from one another in any vertical direction by more than one per cent of the depth. The complete depth was 172 ft. In addition to the freezing pipes a pilot hole was drilled in the middle of each shaft and lined with filter pipes. The freezing plant consisted of one unit of 100 million calories per hour at -20°C (-4°F) and two units, each of half that capacity. The volume of brine pumped varied from 7, 000 to 15, 000 gallons per hour; at first the temperature of the outgoing brine was 32°F. and of the return stream 38°F., at the end of one month the temperatures had been reduced to 2 ° F and 7 0 F, and at the end of two months when freezing was complete to -4°F and -2°F. When the foundations for Grand Coulee Darn across the Columbia River were excavated, it was found that about midlength of the east coffer• darn area, the underlying bedrock is crossed by a narrow ravine 120 feet -31-

deeper than the prevalent surface of the surrounding bedrock. The steep walls of the ravine are about 100 ft. apart where the axis of the da.rn crosses the ravine. The bottom of the ravine is 175 ft. below the surface of the river at its low-water stage. Early in the spring the neighbouring overburden of till started to flow and pushed its way along the f lurne of• fered between the rocky vertical walls. While the bottom of the ravine was exposed for a short time, the contractor tried to halt the slide by a arnaIl concrete arch darn across the ravine but in vain. After other un• successful attempts to stop sliding, it was decided to freeze the entire rnater ia.l in an arch across the slide area between the steep rock walls of the ravine. A radius of 105 feet was adopted for the arch and 20 ft. for its thickness. The refrigerating plant consisted of two arnrnon'ia compr e s s or s that had a c ombined capacity of 80 tons of ice per day, 67 kgrn, calories per sec. The rriater iaI in the arch had an average water content of 32 per cent by dry weight so that its heat conductivity was high. The refrigerated brine was forced through several groups of vertical Ii in. pipes, 43 ft. long protected by envelopes of 3 inch pipes driven into the ground. All told, 377 of these pipes were used. The arch and all exposed mains were insulated with a layer of sawdust 2 ft. thick. It took about six weeks for both c ompres s ors to freeze the arch, but afterwards one c ompr e s s or was able to rnaintain the ternper a tur e of the arch at the freezing point while construction of the daIn was under way. The cost of freezing the arch, which was 100 ft. long, 20 feet th.ick, 40 feet high and contained about 3, 000 cubic yards of rnater ial, was 30, 000 dollars. Freezing saved at least 30, 000 cubic yards of excavation. (The Engineer 165: 183-184, 1938). (Ice and Refrigeration 17: 77, 1937).

In Russia the first ice castle on record was built as a show piece in 1740 and shots were fired on this occasion f r orn guns rnade of ice, long before ice was used for the preservation of food. Artificial freezing of the ground was utilized on a large scale f r orn 1925 on, after the dis• covery of huge pota.e s ium sources near SolikaInsk. For the excavation of the first shaft, 5 In. wide and 125 In. deep, the ground around the pit was frozen, for a width of about 4 rn,, by placing concentric freezing pipes along the periphery, about 1 In. apart. During two rnorrths three compres• sors with a total capacity of 300 rrriIl.i on calories per hour pumped brine at -42°C. through the pipes. Then the construction of the wall of the shaft was begun. It was rnade with cast iron rings and concrete. After five rnore rrionths the shaft had been built to a depth of 125 In. The arnount of heat r ernoved was Ii billion calories. Artificial freezing of the ground was useful during the construc• tion of the Moscow Subway in 1937-38. The ground of Moscow in the Korov section of the subway consists of wet sand and clay of the glacial and Jurassic period, 25 to 30 In. thick, -32-

over limestone. The ground water level is from 5i to 7 m , below the surface. A water -proof stratum is formed by clay lying at a depth of 22 to 25 rn, Thus the total thicknes s of the unstable water -bearing stratum extends to 15 to 17 metres. It yields its water with difficulty and all the inclined shafts and vestibules had to be excavated after artificial freezing of the ground. A wall of frozen ground was produced by drilling a number of boreholes in which freezing pipes cooled by smaller pipes were placed. The ground surrounding the boreholes gradually f r oze, the ice cylinders formed grew and joined the neigh• bouring cylinders until a compact solid layer was produced. The presence of buildings made the use of inclined boreholes unavoidable. The refrigerating plant for freezing the ground around one in• clined shaft consisted of one ammonia compressor for 820, 000 calories per hour and a second compressor for ＳＵＰｾ 000 calories per hour, evaporator, condenser and motors (236 kw, and 184 kw). The temper• ature of the brine varied between -25°C and -20°C. It took 40 days to form an ice wall around the cylinder surrounding one of the inclined shafts, 15m. deep and about 50 m , long. Only a strip of ground 50 to 60 ern, thick on the outer side of the shaft was frozen. Attempts were also made in Russia during recent years to build subterranean storage rooms, with ice walls cooled by refrigerators in the warm season; but apparently the scheme was not satisfactory.

REINFORCED ICE AS STRUCTURAL MATERIAL

Reinforced ice, in particular, ice reinforced by its refrigeration pipes, was proposed by Karl P. Billner for temporary structures such as ice arches erected between the piers of a bridge to serve as supports for the concrete forms, or for roofs of structures where insulation is a chief objective (gasoline tanks). A beam of ice reinforced in this way, 23 in. wide and 24 in. deep, traversed by sixteen I-inch pipes was placed upon concrete supports 28 ft. apart and 13 in. wide. In addition to the pipes through which a continuous flow of brine was maintained, the ice beam was strengthened by Ii in. round steel rods, anchored by i in. steel plates 4 in. from each end of the b earn, together with 20 inclined stirrups. The ice beam was formed in place, it required about four days to freeze dry. After freezing, a brine temperature of 16°F. was maintained; it kept the top of the beam at 30.2 ° F. The beam was loaded vertically at the c entre, through a surface of wood 3 in. x 36 in.; the weight of the beam, pipes and rods was 8, 200 lb. the concentrated load was increased from 4, 000 lb. in steps of 800 lb. until it had attained 10,400 lb. -33-

The rnaxrmum deflection read immediately after the application of the full load was 0.27 inch; 20 minutes later it had increased to 0.37 inch, 40 minutes later to 0.41 inch, after one hour 0.44 inch. After un• loading the deflection went back to 0.07 inch after 20 hours. When a con• centrated load of 4, 000 lb. was then added, the deflection increased from 0.07 to O. 13 inch at the first reading, to 0.21 inch the next day, 0.23 in. on the third day and to 0.244 inch on the fourth day. (Ice and Refrigeration 100: 3-5, 1941).

COEFFICIENT OF LINEAR EXPANSION OF ICE

In the most recent measurements, rods of ice frozen slowly in paper tubes were used, the freezing proceeding radially from outside in. The polariscope gave no indication of any regular orientation of the constituent crystals, but it was probable that the optic axes of the crystal tended to be parallel to the radius (Jakob and Erk).

Thermal Coefficient of Linear Expansion (perpendicular to optic -axis) 6 6 Temperature °C Coefficient x 10 Temperature °C Coefficient x 10

0 52.7 -110 30.6 -10 51.7 -120 27.3 -20 50.5 -130 23.9 -30 49.0 -140 20.4 -40 47.4 -150 16. 8 -50 45.6 -160 13.0 -60 43.7 -170 9. 5 -70 41. 5 -180 6.3 -80 39.2 -190 3.3 -90 36.7 -200 0.8 -100 33.9 -210 -1. 3 -220 -3.3 -230 -4. 5 6 The coefficient of expansion of iron is about 8 x 10- at low tem• peratures and not much over 10 x 10-6 at ordinary temperatures.

TEMPORARY SUPPORTS OF ICE Faced with the necessity of lowering 3, 200 ft of telephone duets 30 in. along an avenue in Br-ook.lyn, the New York Telephone Company had holes dug, six feet apart, under each of the 400 or 500 ft. sections of the duct and 100-lb. cakes of ice 14 x 30 x24 in. placed under the duct as -34-

temporary support. The remainder of the supporting earth was then removed. When the section had sunk 8 in. the remaining ice was taken out and the operation was repeated with new cakes of ice until the section had been lowered the required distance. Each section consisted of nine separate vitrified clay and two wooden conduits surrounding the cable weighing 250 pounds per foot. The weight on each ice support was 1. 500 pounds and if a normal stress of 40 lb. per sq. in. was allowable. a section of 37.5 square inches for bearing surface of the ice was the ITlini• ITlUITl. The use of ice, 60, 000 lb. in all. allowed to lower each section as a whole, without cracks or breaks in the ducts. (Eng. News - Record 11 O. Edison EI. Institute Bulletin 3: 483, 1935).

Ice cakes were used as a m eddum of lowering a new 82. ODD-barrel oil tank, 36 feet to its foundation in Jersey City. Ten cakes of ice 22 in. high were placed between the tank b ottorn and the foundation on a 25 ft. d i arne ter circle. away f r orn rivet sections. All of the wooden horses were then r ern.oved beginning at the centre. (Gas Age 77: 667 June 13, 1935).

ICE AS A BUILDING MATERIAL

No serious att.ernpt s e erns to have been rnade to use ice as build• ing rnater ial except in the construction of ice castles as show pieces. The four explorers on the North Pole ice floe report that for the first tirne in the Arctic they built their kitchen of wet snow that was allowed to freeze during the cool auturnn nights. On 4 Sep terribe r , the leader of the party began to rnode l the walls of the kitchen f r om wet snow. The snow lumps were mixed with water, just as rrias ons on the rriai nl.arid m ix gravel, c ernerrt and water for concrete. A f r arnewor k is set up on the spot where the future walls will rise, and is anchored by crowbars. Then the wet snow is brought and dumped into the f oz-rn s ,

DESTRUCTION OF ICE MASSES BY EXPLOSIONS

The first serious experiITlents to destroy icebergs by high ex• plosives were rriade in 1925 by the Ice Patrol Service. There are two easily recognizable types of icebergs. the solid ice• berg, and the drydock iceberg. The solid berg lies c ornpar a tive l y low in the water, its sides are rounded by the action of water, because it has tipped now this way and now that way. The dry dock bergs consist of two high towers with a lower section between thern, and do not turn over. SOITle of the bergs may weigh over a million tons. In general charges of 210 pounds of trinitrotoluene planted in the ice or used as depth charges under the ice do little damage to large icebergs. Only half the length of a six-pounder projectile will penetrate into the ice when the shot is fired at 150 yards. -35-

PLASTICITY OF ICE

Solid bodies differ from liquids mainly by the ease with which their shape is changed without a change in volume. Changes in shape without changes in volume are brought about quite generally by shearing stresses. If a body is continuously deformed by a small shearing stress, it is called a liquid, whereas if the deformation stops increasing after a time, the substance is a solid. Considered from this point of view, ice is on the borderline between liquids and solids; its coefficient of viscosity (10 13 to 10 14 c. p , s.) places it midway between pitch on one side, and lead, zinc (3.3 x 10 16 c. p, s.) or aluminum (7.5 x 10 16) on the other side. Hence the earlier observers concluded that ice yields progressively when subjected to a constant tension. "The extension increases continuously with all stresses above 1 kgrn, per sq. c rn,, and at all temperatures between _6 0 C (about 21 0 F. ) and freezing!' (Main). Under the influence of the applied tension, the layers nearest to the surface begin to flow and create shearing stresses all through the sample. At the same time ice consists of large single crystals and possesses, therefore, the properties of a solid body, but it shows the behaviour of single crystals rather than that of the fine-grained materials that the engineers use. The main feature of the deformation of large single crys• tals is the discontinuous sliding along certain crystal planes whatever the direction of the applied stress provided that it exceeds a certain lower limit. In single crystals of ice and zinc, for instance, the preferred plane is the basal plane. When a cylindrical test piece of zinc, cut from a single crystal, is subjected to tension, it flattens out at one place, and moderate stress changes the formerly round portion into a thin band equal in width to the diameter of the undistorted section. The flat portion can be stretched con• siderably before it breaks so that the total length of the test piece is more than doubled. The distorted part consists of a large number of layers that slide one upon the other and rotate at the same time about the horizontal direction until their plane becomes nearly parallel to the direction of the applied stress. The deformation of the test piece depends, therefore, not on the direction of the applied force, nor upon the two components at 45 0 into which the force can be resolved, but on the orientation of the crystal plane or planes, in particular, upon the angle which the optical axis of the crystals forms with the axis of the cylinder (when the base of the hexagonal prism acts as sliding plane). As the sliding and the rotation render the crystal layers or sliding planes more and more parallel to the axis of the cylinder when the strength of the applied force is increased, the cylinder becomes more and more difficult to stretch, its plasticity decreases; indeed, cold working is known to strengthen the test piece, be it by distorting the crystal lattice, be it by producing a larger number of smaller crystals or -36-

by both effects. (At 80 0 abs the tensile strength of zinc is 250 to 350 kgm, per sq. em. when the material consists of a single c r ys tal, 300 to 600 kgrn, when the grains have about 0.02 em. in diameter, 1300 to 1800 kgrn, when the grain size is about 0.01 em. ) A single crystal of zinc is difficult to stretch either when the basal plane of the prism is quite accurately perpendicular to the axis of the cylinder. so that the applied force has no component in the plane of the base or when the basal plane is practically parallel to the axis of the cyl• inder so that a plastic deformation is only possible by stretching the crys• tal planes or layers. Depending upon the orientation of the crystallographic axes, there are then two kinds of zinc crystals. plastic crystals and inex• tensible crystals. Thirty years before the laws of deformation of single crystals be• gan to be derived from tests with metal crystals, J. C. McConnell had arrived at most of the main facts in his study of single crystals of ice and pieces of glacier ice. Working first with ice composed of crystal grains (glacier grain) larger than 3 rnrn, in diameter, taken from ice caves at the foot of the Morteratsch glacier near St. Moritz, and then with lake ice built of verti• cal columns a centimeter or less in diameter and 30 cm. in length, with the optical axis parallel to the surface of St. Moritz Lake, McConnell and Kidd found considerable differences in the plasticity of ice under tension; they discovered the influence of the structure of ice on its behaviour, and proved that ice is plastic even in the absence of pressure. The re• sults obtained with ice are difficult to study and interpret on account of the ever present progressive viscous flow which is absent in metal crys • tals. Typical measurements are reported in the table that follows. -37 -

Plasticity of Ice in Tension (according to McConnell and Kidd) Test pieces about 25 ern. long and 7 -10 sq. ern. in cross - section

Elongation per hour Nature of Ice in millionth Load kgm. Max. Mean Duration ern. per ern. per sq. ern. temp. temp. of length DC DC test

Glacier i.c e made up of 160 2.7 -2.5 -3.5 24 hours irregular grains, max. Glacier ice max. rate 68 2.55 -2. 5 -4.5 23 hours min. rate 13 2.55 -6.0 -9.0 3 days Total elongation 3% of original length in 25 days. The rate of extension at -40°C is about double that at -9 DC.

Glacier ice, large single crystal with optical axis at 70° to the axis of the test piece (stretched by 4% of its length in 3t days).

Max. rate 18, 800 2.5 -2. 1 -2. 1 10 min. Min. rate 54 1, 45 -6.0 -10.0 16 hours Lowest temperature 65 1. 45 -9.0 -10.5 12 hours

Lake ice length perpendicular to optic axis, and consisting, after tests, of about 30 columns running the full length of the bar 4.0 2. 1 o -5. 5 7 days Lower temp- 7.6 2.8 -4.0 -5. 5 2 days

Lake ice optic axis at 45 to longitudinal axis of test piece

340 2.75 -5. 6 - 5. 8 6 hours 100 2.75 - 5. 6 -6.0 16 hours Icicle with small grains 41 2.2 0.0 0.0 5 days -38 -

Sim.ilar variations in the results are obtained when pressure is applied to ice crystals. For three pieces of glacier ice composed of grains about 7 rum. in diameter and subjected to a pressure of 3.2 kgrn, per sq. cm.• the mean rate of contraction was, respectively, 350 millionth, 560 millionth and 70 millionth centim.etre per hour per centimetre length. Pieces of lake ice compress ed in a direction perpendicular to the optic axis showed a progressive reduction in length equal to 10 millionth c rn, per hour per c rn, length under a load of 3. 7 k.grn, per sq. crn, The values obtained by McConnell and Kidd for the progressive yielding of ice under loads ranging from Ii to 3 kgrn, per sq. crn, are in good agreement with the results deduced from recent tests on ice frozen in a mould and subjected to loads of I to 5 kgrn, per sq. ern. main• tained for a month (30 January to 28 February, 1938). The average tem• 0 perature was - 5 0 C (23 F), the ice consisted of fine grains.

Pressure kgrn, per sq. em. I 2 5 Rate of contraction millionth 3 6.25 46 em. per hour per em. These experiments suggest that progressive yielding is propor• tional to the applied load so long as the stresses are smaller than about 2 kgrn, per sq. em. and increase more rapidly at higher loads. Ex• amination of thin sections of the test pieces before and after the test under a polarization microscope show that the deformation is accompanied by sliding and rotation of the crystal plane (Bader). As a result of these and similar investigations it may be stated that ice yields progressively under stress, at the rate of at least a few millionths centim.etre per hour per centimetre length when the load is 1 kgrn, per sq. crn, This rate increases when single crystals are present in which the sliding planes form a finite angle with the direction of stress and also when the stress exceeds a few kgrn, per sq. ern. The progressive yield consists of shearing parallel to the sliding plane. -39-

REFERENCES Adams, J. M., and W. Lewis. The production of large single crystals of ice. Rev. Sci. Instruments. Vol. 5, p. 400-402, Nov. 1934. Bader, H. "Der Schnee und Seine Metamorphose", Beitrage zur Geologie der Schweiz - Geotechnische Serie - Hydrologie, Vol. 3, Bern, 1939. (in German) Bell, G. G. Results of experiments on strength of ice. Maine Soc. of Civil Engineering, Vol. 1, p. 41-46, 1911. Bernstein, S. Railroad ice crossings. Trudy Nauchnoteknicheskogo Komiteta Narodnogo Korni s s a r iata Putei Soobshchcnia, Vol. 84, p. 36-82, 1929. Billner, K. P. Ice and refrigeration, Vol. 100 p. 3-5, Jan. 1941. Boyle, R. W. and D. O. Sproule. Velocity of longitudinal vibration in solid rods with special reference to the elasticity of ice. Can. J. Research, Vol. 5, p , 601-618, Dec. 1931. Brockamp, B. and H. Mothes. Seismic investigations of the Pasterze Glacier. Z. Geophysik, Vol. 6, p. 482-500, 1930. (in German) Brown, E. Experiments on strength of ice. Appendix F, p. 423 -453, May 20, 1926, (In: Report of Joint Board of Engineers on St. Lawrence Waterway Project, Nov. 16, 1926. Ottawa, F. A. Acland).

Ewing, M., A. P. Crary, A. M. Thorne, Jr. Propagation of elastic waves in ice, Part 1. Physics, Vol. 51, p.165-168, June 1934. Finlayson, J. N. Tests on the shearing strength of ice. Can. Eng. Vol. 53, p • 10 1 - 103, J ulY 5, 19 27 . HaefeLi, R. "Schneemechanik" from "Der Schnee und Seine Metamorphose", Beitrage zur Geologie der Schweiz - Geotechnische Serie - Hydrologie, Vol. 3, Bern 1939. (in German) Jacob, M., and S. Erk. Thermal expansion of ice between 0 0 C and -253 0 C. Z. g e s , K:tlte-Ind., Vol. 35, p. 125-130, 1928. (in German) Koch, K. R. The elasticity of ice. Ann. Physik, Vol. 45, p. 237 -258, 1914. Komarovskii, A. N. Methods of calculating the magnitude of the pressure exerted by the ice cover. Gidrotekhnicheskoe St.roitel! stvo, Vol. 2, No. 11-12, p. 24-29, 1931. (in Russian) McConnel, J. C., and D.A. Kidd, On the plasticity of glacier and other ice. Proc. Roy. Soc. (London), Vol. 44, p. 331-367, 21 June 1888. Moskatov, K. A. Landings of airplanes on ice. Trans. Arctic Irist; , USSR. Vol. 110, p.43-55, 1938. (ATR Translation 225). -40 ...

Main. J. F. Note On some experiments on the viscosity of ice. Proc. Roy. Soc. (London), Vol. 42, p. 491-500, 9 June 1887.

Miigge, O. Further experiments on the translation of ice and comments on the importance of the structure of the Greenland Ice Cap. Neues Jahrb. Mineral. Geol., Vol. 2. p. 80-98, 1900. (In German)

Nazarov, V. S. Contribution to the study of the properties of sea ice. Transactions, Arctic Institute. USSR. Vol. 110. p. 101-108. 1938 (in Russian)

Romanowicz, H. and E. J. M. Honigmann. Tensile and compressive strength of ice. F'o r s ch, Gebiete Ingenieurw. A. Vol. 3:99, March-April 1932. (in German)

Rothrock. A. M., and R. F. Selden. Adhesion of ice in its relation to the de-icing of airplanes. NACA Tech. Note No. 723, Aug. 1939.

Sellerio, A. Adhesive forces which manifest themselves during solidifica• tion. Physik z.• Vol. 34. p. 180-181, 15 Feb. 1933. (in German)

Stefansson, V. My life with the Eskimo. Collier-MacMillan, 1962. (Most recent edition)

Tammann. G. and K. L. Dreyer. Naturwis s ens chaften, Vol. 22. No. 37, p. 613-614, 14 Sept. 1934. (in German)

W einberg. B. Bulletin of the Arctic Institute of USSR No. 8-9, p. 369-375. 1936. (in Russian)

Weinberg. B. The mechanical properties of ice. Intern. Geodet, Geophysl. Union. Assoc. Sci., Hydr-ol,, Bulletin 23, 1938.

Witman, F. F. J and P. P. Shandr ikov, T'r-ans , , Arctic Institute, USSR. Vol. 110, p. 83-100, 1938. (in Russian) APPENDIX A

SUMMARY OF DATA ON REINFORCED ICE FROM FILES OF THE NATIONAL RESEARCH COUNCIL OF CANADA

(a) Flexural Strength

(1) Laboratory Tests on 2- by 4- by 36-in. Beams.

Modulus of Rupture Construction (psi)

Chipped ice and water - no reinforcement 194 Chipped ice and water, wood tensile reinforcement (1. 56 per cent) 277 Chipped ice and water, wood tensile reinforcement (1. 56 per cent) plus web O. 3 ..in. Dwire 801 Chipped ice and w ate r , steel tensile reinforcement (0. 44 per cent) 632 Chipped ice and water, steel tensile reinforcement (O. 44 per cent) plus web 960 Chipped ice and water, steel tensile reinforcement (0. 31 per cent) plus web 986

Pykrete 6 per cent dry fibre, no reinforcement 712 Pykrete 9 per cent dry fibre, no reinforcement 884 Pykrete 10 per cent dry fib r e, no reinforcement 1050 Pykrete 10 per cent dry fibre, wood or steel reinforcement 2140

i2l Performance of Various Micro Reinforcements (2 .. by 4- by 36-in. Beams)

Ratio of Modulus No. of of Rupture Material Specimens (average) Water 9 1.0 Snow and water 5 1.11 Peat Moss 2 0.81 Saw dust 2 1. 86 Hay 3 2. 15 Newspaper 6 2. 5 to 4. 7 Wood Pulp 6. 5 per cent 6 2.8 Wood Pulp 10 per cent 7 4.3 Cotton 2 4.33 A-2

(3) Beam Tests. Rapid Loading of 4%- by 10- by 29-in. Beams

Modulus of Rupture (psi)

Plain ice (no reinforcem ent) 100 Plain ice diagonally reinforced 1360 Pulp ice diagonally reinforced 1500

(b) Tensile Strength

(I) 14 per cent ground scotch pine at 5° F:

Ultimate tensile strength parallel to layers = 700 psi Ultimate tensile strength normal to layers = 300 psi

(c. f. ice c::: 100 psi)

(2) 10 per cent wood pulp (T unknown)

U. T. S. (4 specimens) = 346 psi U. T. S. (ice, 17 specimens) = 111 psi tc) Compressive Strength (unconfined)

No significant difference between pure ice and pulp ice. Typical range of values for both materials is 300 to 1400 psi.

(d) Creep Properties

(1) Investigations indicate creep rate for flexural loading of pulp ice (8 per cent) 2- by 4-in. beams at 12° F is given by ..11 3. 5 Creep rate = 1. 25 x 10 (f) per cent per hour

where f is the extreme fibre stress (psi).

(2) A load of 100 psi on 8-in. diameter cylinder 7 in. long for 8 weeks at 5° F gave a rate of 0.85 per cent per year. A-3

te) Bond Strength

(1) (Temperature = 23 0 F)

i-in. oak dowel 203 psi (plain ice) 116 psi (pulp ice) 3/8-in. plain steel 202 psi (plain ice) 102 psi (pulp ice)

Creep tests at 15 psi: (steel failure after 90 hours) (wood no failure after 200 hours)

{f} Ice Production

(I) Test pad on lake (20 by 20 ft); ice grown at 2 to 4 in. per day (Temp. data in report).

(2) Tests indicated a rate of O. lin. /hour at 240 F flooding in l/l6-in. layers.