1994 Arctic Ocean Section
Measurements of Ice Mechanical Properties
F. Mary Williams
During AOS-94, ice mechanical properties were measured by the Institute
for Marine Dynamics. Williams (1994) gives details on the methods and re-
sults. The program was supported by Ship Safety, Canadian Coast Guard, as
part of a broad ship technology program.
Under the ship technology program, ice loads at three locations on the hull
of the Louis S. St-Laurent were monitored throughout the voyage, and signifi-
cant events were recorded. Ship performance was documented by continuous
recording of propulsion system parameters, as well as ship speed and position.
The ice properties that influence hull loads and ship performance are the thick-
ness, strength and density of the ice and the quality of the snow cover.
Ice temperature and salinity were measured at 10-cm intervals, and ice
density was measured at selected depths in vertical ice cores. Two cores were
taken at every science station in the ice using the Rapid-Core, a crane-deployed
coring device operated from the deck of the ship. Additional cores at sites
distant from the ship were taken using a hand corer. Often, average ice temper-
atures were 2C, and average salinities were around 2‰. The ice contained
large brine channels, and brine in the upper layers had drained out.
Measurements of ice density from core samples are difficult at these temper-
atures. The result depends strongly on the amount of brine trapped in the
sample, which in turn depends on both the structure of the ice in the core and
sample handling. Most of the local density values were between 0.82 and 0.92
Mg/m3.
The inertial and buoyant forces of ice on the ship depend on the global, in-
situ ice density. This quantity, determined from freeboard measurements and
adjusted for the snow burden, was consistently between 0.92 and 0.93
Mg/m3.
A beam test is a direct measure of the flexural strength of the ice. When
logistics permitted, beam tests, in a standard size and configuration (Williams
and Parsons 1994), were carried out on the ice immediately after cutting the
samples. A typical result is a series of eight beams of columnar-grained ice at
1.8C, with an average flexural strength of 499 kPa. Some beam samples
were cold soaked and tested in the coldroom onboard the ship.
F. Mary Williams is with the Institute for Marine Dynamics in St. John's, Newfoundland, Canada.
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