Publisher’s version / Version de l'éditeur:
Technical Note (National Research Council of Canada. Division of Building
Research), 1967-06-01
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Observations on the Quality of the Ice in Kingston Harbour, 20 March
1967
Gold, L. W.
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NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=56d6c541-f6d4-46e6-8324-0b31f47a82fe https://publications-cnrc.canada.ca/fra/voir/objet/?id=56d6c541-f6d4-46e6-8324-0b31f47a82feDIVISION OF BUILDING RESEARCH
No.
NATIONAL RESEARCH COUNCIL OF CANADA
488
NOTJE
']['EClHI N][ CAlL
PREPARED BY L. W. Gold CHECKED BY APPROVED BY N.B.H.
June 1967
PREPARED FOR Inquiry and record purposes
SUBJECT OBSERVATIONS ON THE QUALITY OF THE ICE IN KINGSTON
HARBOUR, 20 MARCH 1967
In response to an invitation from Brigadier H. W. Love, Director, Montreal Office of the Arctic Iristitute of North America, observations were made on the quality of the ice in the harbour of Kingston, Ontario, at the time of the testing of the Alexbow Ltd. ｰｲｯｴｯｴｹｰ･ｩ｣･ｾｲ･｡ｫｩｮｧ plow. The testing of the ice-breaker bow was carried out during the week of March 20 to 24 and the observations were made on the ice on the 20th of March.
FIELD OBSERVATIONS
Most of the observations were made at a site about one-half mile south of the dock of the Kingston Shipyards and 300 feet from shore.
Measurements along the line from the dock to the observation site showed that the ice cover was between 12 and 14 inches thick. The ice was generally clear and in many areas cracks could be seen at the underside of the cover. The surface of the cover was about 50 per cent covered with white patches. These appeared to be due to drifted patches of snow becoming saturated with water and subsequently freezing. A profile of the cover at one of the white areas is shown in Figure 1.
There was a ridge in the cover about 300 feet south of the dock. This ridge ran approximately perpendicular to the shore to a point of land on the east side of the harbour. It was composed of blocks which, at the surface, were up to about 6 feet square and 6 inches thick. The top of the ridge was
2
-about 3 feet above the surface of the cover. Three separate blocks with water in between were encountered in drilling from the top of the ridge to a depth of 3.5 feet.
The ice cover was highly cracked, the polygonal areas formed by the cracks having a maximum dimension generally not exceeding 36 inches. Some of the cracks extended completely through the cover, but were open only from the surface down to a depth of 4 to 6 inches.
A block about 20 inches square and 12i inches thick was cut from the cover at the observation site. Although the temperature at the surface and throughout the cover was 32o F, the action of the saw indicated that the ice was quite hard. This block was cut in half, placed in insulated boxes, and brought back to Ottawa for testing.
The clear ice cover contained many cavities that appeared to be arranged in curved planes. On removing the block from the cove r, it was seen that these planes of cavities extended from the surface to about 4 inches from the bottom. The concentration of cavities was greatest near the surface and gradually decreased with depth below the surface.
The cavities had the appearance of old "Tyndall flowers." 'Tyndall flowers" are formed by internal melting due to absorption of radiation.
Observations made from the ice-breaker bow during the afternoon indicated that the thickness and quality of the ice in the vicinity of the docks of the Kingston Shipyard Co. were the same as those at the obser-vation site.
LABORATORY MEASUREMENTS (1) Grain Size Measurements
Thin sections were cut from the block samples parallel and per-pendicular to the direction of freezing of the water, and observed with polarized light. The thin sections perpendicular to the direction of freezing were taken at depths of 1,2,3,4,5,7,10, and 12 inches beneath the original ice surface. The sections parallel to the direction of freezing showed that the ice had a columnar structure with the long axis of the columns perpendicular to the surface of the ice cover. Average grain dimensions perpendicular to the long axis of the columns increased with distance beneath the surface. Most grain boundaries were inclined to
the vertical. As a result, many of the grains were "cut-off" by neighbouring grains, particularly near the surface. The sections perpendicular
3
-to the direction of freezing showed considerable intergrowth at the grain boundarie s. Average grain dimensions perpendicular to the long direction of the columns are given in Table 1. These values must be considered as rough estimates.
Observations were made on the thin sections on the crystallographic orientation of the grains. It was found that the crystallographic axis of hexagonal sym.m.etry, that is the "CII axis, had a marked tendency to be
parallel to the long direction of the grains. The basal plane of the grains (the plane of easy slip), consequently tended to be perpendicular to the long direction of the grains.
(2) Measurement of Compressive Strength
Rectangular specimens, 2 by 4 inches in section and 10 inches long, were cut from the top, middle, and bottom of the block samples; two were prepared for each level. These specimens were cut so that the long direction of the grains was perpendicular to the 4 by 10 inch face. The specimens were cut from the sample with a band-saw and brought to their final dimensions with a milling machine.
The compressive load was applied to the specimens on the 2- by 4- inch face, that is, in a direction parallel to the original surface of the ice cover and perpendicular to the long direction of the columns. All specimens were loaded to failure as quickly as possible in a 10-ton Carver hydraulic press. The te sts were carried out in a cold room maintained at 14°F. The compressive strength and the time to failure for each specimen are given in Table 1.
There is a marked increase in the compressive strength with distance below the surface of the cover. The tests indicate that the ice had a compressive strength of about 625 psi in the upper 4 inches of the cover, about 1000 psi in the middle, and about 2000 psi in the bottom. These results show that the ice in the vicinity of the docks at Kingston Har bour was of good quality.
In all case s, failure occurred by the abrupt lIexplosionll of the specimen in the testing machine. Prior to sudden disintegration, crack formation was observed. The cracks tended generally to be parallel or perpendicular to the vertical faces of the specimen, with the plane of the crack parallel to the direction of the load. Time until failure generally increased with distance from the upper surface of the cover.
,
4
-The specimens from the upper 4 inches broke within 3 seconds of the beginning of the application of the load. In the case of the specimens taken from the bottom 4 inches, the maximum load was attained very
quickly and then the specimen yielded. The hydraulic system of the testing machine had to be pumped rapidly in order to maintain the load. As a result, the specimens underwent considerably more deformation prior to the final failure than did those from the higher levels. Cracking was more extensive for the se specimens than for those from the upper and middle part of the cover. In one case, the internal cracks formed were
initially uniform in distribution, but subsequently began to concentrate along planes tending in the direction of the planes of maximum shear.
The times to failure for the two bottom specimens were 12 and 25 seconds. In all cases the type of failure observed and the characteristics of
internal cracking during load are consistent with the columnar -grained structure of the ice and the preferred crystallographic orientation of the grains.
CONCLUSIONS
The ice cover in the vicinity of the docks at the harbour in Kingston, Ontario, on 20 March 1967, was clear and between 12 and 14 inches in thick-nes s. The ice had a columnar -grained structure, with grain size increasing with distance from the surface. The crystallographic axis of symmetry tended to be parallel to the long direction of the grains. Internal cavities were present, the concentration of the cavities increasing toward the surface.
The ice was of good quality. Its compressive strength increased with dis-tance below the surface, being about 625 psi in the upper 4 inches and 2000 psi in the bottom 4 inches. The decrease in strength toward the surface was probably due to the presence of the cavities and the decrease in the average grain size. The compressive strengths observed are comparable with those for good quality ice with the same structure characteristics and c:rystallographic orientation.
ACKNOWLEDGEMENT
The author wishes to express his appreciation for the assistance of Mr. W. Ubbink in making .the field observations and carrying out the laboratory tests.
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-TABLE I
STRENGTH PROPERTIES AND GRAIN SIZE PERPENDICULAR TO LONG DIMENSION OF GRAINS FOR ICE FROM KINGSTON HARBOUR
Specimen No. Location in Compres sive Time to Average grain COver strength, psi failure, size, inches
seconds 1 Top 687 2 1.0 2 Middle 1285 5 1.5 3 Bottom 2185 25 2.0 4 Top 538 3 0.7 5 Middle 813 3 1.5 6 Bottom 1862 12 2.0
