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Technical Note (National Research Council of Canada. Division of Building Research), 1953-09-01
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Tibbetts, D. C.
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DIVISION OF BUILDING RESEARCH
No.
NATIONAL RESEARCH COUNCIL OF CANADA'
151
NOTE
'f
E
C
JH[
N II
(!
AlL
NOT FOR PUBLICATION FOR INTERNAL USE
PREPARED BY D.C. Tibbetts CHECKED BY APPROVED BY
PREPARED FOR General In:rormation DATE September,
1953
SUBJECT Construction of an Offshore Pier in the Lower
St. Lawrence Ice Effects
The Department of Transport is now considering the
design of an offshore lighthouse pier for the Lower St. Lawrence. The pier, when completed, will serve as a permanent aid to navigation
and will replace a lightship now on station. In addition to the
provisions which must be made for tide, wind, and river currents careful study must be given to the forces that may be exerted by
sea and river ice on the proposed structure.
Mr.
Walter Manning,Chief, Aids to Navigation, has requested this Division to assist, where possible, with particular reference to the ice aspects of the probl em.
LOCATION OF PROPOSED PIER
A Department of Transport lightship is on station during
the shipping season, in apprOXimately
6
fathoms of waterimmedi-ately northeast of 'White Island Reef. White Island is ab0ut 10
miles up the St. Lawrence from the mouth of the Saguenay River
and is
5
miles offshore in midstream. It 'is proposed to replacethe lightship by a pier located about 1 mile southwest of the
present station in about
4
fathoms of water. A navigation aid atthis point serves both the north and south channels of the river. Charts of the area have been received by the Division of Building Research and are retained in the Draughting Section.
SITE CONDITIONS
Although boring operations at the site have been limited due to the difficulty of keeping the drill barge on station, core
samples of the river bottom have been taken. These borings show
the bottom to consist of a medium hard shale with a bedding plane,
on the average, of
10
degrees. The unevenness of the river bottomat this point makes it necessary to level the site to reduce shearing of the near-vertical bedding planes.
The tidal effects at this point in'the River are
considerable and these, together with a variety of river currents, make it unpractical to design a structure to resist forces in one
2
-with accompanying ice is such as to sUbject the structure to strong rorces rrom almost every direction.
Currents
(1) Laurentian: this current works upstream in diminishing
volume to a turn-around point near Red Islet. It keeps
to the north side of' the Gulf of St. Lawrence but its presence at the Gulr-end of its path is not sharply in evidence;
(2) The Cross Currents: these currents are continually
delivering "Laurentian" water across the Gulf to the Gaspe current on its south shore;
(3)
Gaspe Current: this current originates close to RedIslet and flows near the south shore of' the Gulr as
far as Cape Gaspe. The Gaspe current flows with great
strength at an average speed of 2 knots and an effective width of 12 miles.
Mr. A.K. Laing, Assistant Chief, Aids to Navigation,
states that there is a reversal of' current every
6
hours due totidal changes. This is to be expected where speed of tide in
knots is suf'ficient to reverse the main river flow in one instance and to add to this flow on the ebb.
Tides
Ocean tides move upstream to a point a rew miles above Quebec City so that there is a definite tidal effect at White
Island. At the proposed pier site tides have been recorded and
are shown to have a 12-f'00t rise on the neap and a spring tide
rise or 16 feet. On the average, f'lood tides have a speed of
4
knots with a rate or 2 knots per hour on the ebb. Some ihelteris reportedly afforded by the White Island Reef at ebb tide.
At low tide the pier would be standing in about
24
feetof water with an expected rise of 16 f'eet on the spring tide giving
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v3
-Salinity
The section ｯｾ the river between the mouth of the
Saguenay River and lIe aux Coudres serves as the mixing pot for the fresh waters of the river and the salt waters of the Gulf.
The limits ｯｾ this estuary are ｾｩｸ･､ by the change in the
character of its waters which at the west end are almost fresh (density 1.005) and, in summer, warm; and when opposite the mouth of the Saguenay are definitely cold and saline (density 1.02). ICE OBSERVATIONS
The Gaspe current is rated as a very generous contributor
ｯｾ drift ice drawing much ｯｾ its supplies in the early winter
ｾｲｯｭ the fresh water river between the lIe aux Co.udres and Three
Ri vers and later from the shallows and shoals along both shores
of the ｇｵｬｾ from. the lIe awe Coudres to the eastern end ｯｾ
Anticosti Island. Little drift ice originating west of Three
Hivers reache s the ｇｵｬｾＮ The north channel fro m the we st end of
Anticosti to Red Islet remains fairly clear of ice all winter and the Gaspe current sweeping along the south shore, although heavily
laden with ｾｬｯ｡ｴｩｮｧ ice, ｾｬｯｷｳ like open water without check or
hindrance.
ｾ
The active ice movement is/largely due to tidal
fluctua-tions and a barrier across the Gulf ｾ lIe aux Coudres with the
assistance of levees could almost completely cut off the supply
of drift ice to the Gulf areas from the upper shoals. Substantial
quantities ｯｾ drift ice might be expected to form in the Gulf ｯｾ
St. Lawrence itself after February 1, but this ice would not be of great thickness nor would it be hard frozen if compared with
､ｾｩｦｴｩｮｧ ｾｲ･ｳｨ water ice.
4
-TENTATIVE DESIGN OF PROPOSED PIERIn view of the many directions in which forces are expected to be exerted against the pier, present plans call for
a cylindrical shape of structure. The diameter will be in the
order of 70 to 80 feet and the height about 60 feet. Some
ｴｨｯｾｴ has been given to the idea of assembling the cylinder at
Quebec Drydock this winter and floating it to the site in the
spring of 1954. At the site the structure will be sunk and
dowelled to the reef as required and the whole filled with concrete. The expected weight of the completed pier is expected to be
approximately 10,000 tons.
It is intended to flare the cylinder inward at the ice surface, the idea being to permit a's much of the ice as possible coming in contaot with the pier to "ride off" thus helping to
reduce impaot. The actual height at whioh to begin flaring the
pier will be difficult to determine and will be determined somewhat by the ice conditions at a particular water-level or phase of tidal flow, there being a difference of 16 feet between
high and low water. The super-structure will produce a dead
load of about 500 tons and it is hoped that this will be sufficient to prevent shearing at the critical section.
On the basis of a crushing strength for ice at 400 p.s.i. the present design provides for a contact surface of two-thirds
of the pier diameter to a depth of 6 feet. If additional strength
of ice is later assumed the extra thrust will have to be taken
｢ｾ dowels or pins in bed-rock.
The expected cost of the pier is expected to be about
$750,000. This is high for a navigation aid but it would cost
approximately $1,000,000 to replace the lightship and in addition the annual maintenance and operating costs are such as to make a pier desirable where possible to construct.
INVESTIGATION BY THE DIVISION OF BUILDING RESEARCH
The Division of Building Research has been asked to assist specifically with the ice problem which is of a special nature in that both sea and river ice are encountered at White
Island.
A literature search has been made and in addition the National Research Council Liaison Office in Washington has been
contacted in order to determine to what extent work of this nature has been conducted elsewhere in the world.
As a result of correspondence with Washington on the subject Commander K.W. Donnell of the United States Coast Guard
met with Mr. Laing in Ottawa June
25, 1953,
to discuss offshorepiers. The United States, while anxious to eo-operate where
possible, have apparently little or no information that would be
usef'ul in this particular case. Mr. Manning has contacted other
countries on the subject but there appears to be no similar conditions existing in other parts of the world.
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, ';(" • ｾＮ Iｾ -.J Ｎｾ｟ ..\)'The Division of Building Research has submitted some information on the crushing strength of ice (Inquiry No. 1-2882) but as temperature has a considerable effect on the strength of ice
the Division has been asked to look into the effects of water and
Burrounding air temperatures on ice. The temperature of the
St. Lawrence River at White Island in winter is about 28°F.
It has been suggested to Mr. Laing by this Division
that the impact of floating ice on structures should be carefully
studied. Impact is thought to be a more important factor in
the design of piers than the crushing strength of the ice. REFERENCES
In an endeavour to determine the effects of drifting ice on structures and the crushing strength of ice at'various
temperatures the following literature has been reviewed.
Informa-tion not included in the text of this.note has been summarized under the appropriate reference.
(1) Winter Navigation on the St. Lawrence - "A Suggested Method 'of Overcoming the Limitations·Due to lee".
(a) The Dock and Harbour Authority - November 1950. (b) The Dock and Harbour Authority - December 1950. (2) "Ice Pressures on Dams", by Howard T. Barnes, 1928. (3) "The Ice Packs" - Lower St. Lawrence - E.I.C. Journal
October, 1951.
(4)
"Bridge Piers" - Handbook by Merriman&
Wiggins.(5) Symposium on Ice Pressures. File copy obtainable from
Mr. Leggetts office.
(6) Technical Translation Series, Division of Building Research,
Article by Lofquist. ｾ
Transactions of American Geophysical Union, v28-l, p.116,
by Robert P. Sharp (Moskatov 1938) - "Most sea ice has a
breaking ,strength of 10 to 15 kg/cm2 in contrast with the
30 kg/cm2 of fresh water iceft
•
(8) Bibliography tlSIPREtt - Sunnnaries
(a) "Analysis of the Compressive Strength of Ice", by
F.F. Vitman and N.P. Shandrikov. Arkticheskogo
Instituta, Leningrad, 1.938, 110:83-100 DLC, G600.
L4.
V.110 - Samples 5 x 5 x 5 em.(i) maximum strength of sea ice is about 60 kg/cm2• (ii) strength of upper transparent layers is greater
than lower, porous layers. .
(iii) strength increases as temperature 1s lowered.
Average strength at -60°C. was
4
times as large:,-: - ｾ (.I f r .. ::: " v l- , ( j v ｪｾ l oJ ','- Ｇｾ... e- "
-
, ｾｾｲ 0:::. (')ｾ ｾＭ ｾＭＭＺ -- ｾ :j rt J" :ｾＬ I' ( , In.,
J'" :"1\..0, ＧＮｾ Jｾ r - (. )' '''J , J c;" • J..
- o ; ( r. :.. h. •--
t - C > 3 . .J.. ｾ !' I •. \ . = C , r ｾ . ;-" ,( ｪＧｾ C' :Jr ( ' . l (' ;. , ._(' :.. , '1'l '....
'- .-,. (' (.. u ｾ.
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Ｇｾ f, -I, t . , ［ﾷＮＱＰｾ ｾ _. .:: ＮｾＮ . ... rＭＧｾ , . J .. ':"1 ._<II. I-e: I· '3 c ....".
ｾＧｬ ｾＧ" , :..6
-(b) "Observations on the Crushing Strength of Ice", by William Ludlaw, Proceedings of the Engineering Club
of Philadelphia, 4:93-99, incl. tables 1884 DLC, TA 1. E7, V.4 - maximum pressure required to crush ice of the clearest and most compact structure is 1,000 p.s.i.
(c) G.G. ｂ･ｬｬｾＭ structures subject to blows from floating
iee shoUld resist from 10 to 12 tons/sq. ft.
(9)
AI
file D.B.R. LibraryNotes by Mr. Legget - "Tarr and Von Engeln (1915) state
in their conclusions that 'Variations of temperatures between limits of 10° and 25°F. do not seem to exert a notable ef!ect on the crushing strength of ice'".
(10) "Arctic Ice and;the Warning of the Arctic", by N.N. Zubov, D.S.I.S., Defence Research Board, Canada, 1950.
"The strength of ice is very much dependent on its
tempera-ture. At -90°C. its strength is approximately equal to
that of well-fired brick and increases very little as the
temperature is lowered below that point. As the temperature
rises toward the melting point its strength rapidly declines; at still higher temperatures the ice turns to a porridge-like mass.
The temperature of sea ice formation is continually changing
but that of the under surface remains constant ｡ｰｰｲｯｸｩｭ｡ｴ･ｬｹｾ
equal to the freezing point of sea water, i.e. -1.6° to -1.8°C. The temperature of the top surface approximately follows that
of the atmosphere, sometimes dropping to -40°C. Consequently
the ice at the bottom of the field does not change in bulk while at the upper surface it is either swelling or shrinking
by reason of thermal expansion and contraction.
(11) Transactions of the Arctic Institute (U.S.S.R.) Vol. 110, 1938, p.43 to 55.
Abstracts: Arctic manual p.l03, para. 168.
Sea ice: the lower the air temperature at which sea ice
forms, the stronger the ice. In early winter sea ice is
generally not as strong as fresh-water ice at thicknesses of about 1 ft., however, the strength of the two becomes nearly the same by spring except during a thaw, when sea
ice is usually the stronger of the two.
AppendiX I. Summary - "The Landing of A/C on Ice", by
K.A. Moskatov.
The mechanical properties of ice of salt water origin have, on the average, half (sometimes one-third) the value of
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-those of fresh water ice. This depends on the degree of
salinity and temperature of formation. In the East
Siberian Sea 1929-30, ice had a compressive strength of
426 p.s.i. and a bending strength of _'l42 p.s.i. In the
Laptyon Sea and in the Kara Sea (west of Siberia) ice had
a eompressive strength of 213 p.s.i. and a bending strength
