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Geotechnical News • June 2017
A later study in 1952, carried out
jointly by the Division of Building
Research, National Council of Canada
and the University of Manitoba, con-
firmed an ultimate bearing capacity of
6,200 pounds per square foot, which
correlated very closely with the theo-
retical value based on a soil mechan-
ics analysis.
Two Canadian cases of recorded long-
term building settlements, erected
before the science of soil mechanics
was applied to building foundations,
are also noteworthy.
Construction of the CPR Empress
Hotel at James Bay, Victoria began in
1904 on a site reclaimed from the sea.
Marine clay underlies the building to
a thickness ranging from a few feet to
more than 100 feet. The building was
constructed on a foundation of 1,853
timber piles, each about 50 feet long.
Observations began in 1912, after
settlements were first noticed, and
have continued ever since. By 1971
the differential settlement across the
building north to south amounted to
some 30 inches, although this was not
noticed by the casual visitor.
After 50 years of service, the owners
were faced with the decision whether
to extend the life of the elegant struc-
ture or to replace it with a modern
building. On the basis of a comprehen-
sive study, R.M. Hardy concluded that
the rate of settlement was decreasing
and would be within acceptable limits.
As a result, in a multi-million dol-
lar program, the building was reha-
bilitated under the appropriate name
Operation Teacup.
The Victoria Memorial Museum
(National Museum of Canada) build-
ing in Ottawa, a massive four-storey
structure, 400 feet long and 150 feet
wide, with heavy sandstone bearing
walls, rested on spread footings. Since
completion of the building in 1910,
footing loads, which varied from 12 to
4 tons per square foot, caused a differ-
ential settlement in 40 years of more
than 1 1/2 feet.
Unlike the Empress Hotel, the build-
ing showed distress from the start and
was completed with much difficulty.
Basement and ground floors and the
exterior walls, supported on both
exterior and interior footings, showed
severe distortion and cracking. The
upper storeys, carried on plate girders
spanning the exterior walls, suffered
less differential settlement. By 1916 a
tower at the front of the building was
out of plumb by more than a foot and
the upper portion had to be removed to
prevent complete failure.
In the early 1950s, borings and studies
of the museum by DBR/NRC revealed
that the building was underlain by 50
feet of sensitive, compressible marine
(Leda) clay, which graded into clayey
silt, sand, and glacial till at increasing
depth, with bedrock at 132 feet.
Birth of Soil Mechanics
Prior to the 20th century, any textbook
on foundation and earthwork engineer-
ing divided soil into several categories
– gravel, course and fine sand, silt, and
soft or stiff clay. Various allowable
bearing values, based on empirical
equations or rules, were assigned to
these different materials. But only one
variable, the type of soil, was consid-
ered. Equally important mechanical
properties of the soil, such as density,
water content, and compressibility
were ignored.
In those early ears, the foundation
design of buildings or of structures
involving deep excavation or tunnel-
ing was based on primitive geologi-
cal surveys of the materials located
beneath the construction site. Founda-
tion on bedrock was preferred. But
where bedrock could not be reached,
over soft soils the bearing load was
spread out by use of spread footings or
rafts, often with disappointing results,
as we have seen with the Victoroa
Memorial Museum and the Transcona
Grain Elevator.
When in doubt, pile foundations were
the rule. At the beginning of the 19th
century, empirical pile formulas were
developed, with the bearing capacity
of each pile computed on the basis of
the work performed by the hammer in
driving the pile into the ground, the
depth of the pile’s penetration, and the
resistance of the soil. While helpful,
these formulas did not preclude the
possibility of an entire group of piles
settling. If the pile tips were located
above clay soil, excessive settlement
often took place as a result of the
gradual consolidation of the clay soil
beneath the piles, as we have noted
with the Empress Hotel.
The mechanics of landslides were not
understood, and rational methods for
evaluating the safety of slopes with
respect to sliding were unknown. The
only analytical tools at the disposal
of civil engineers were the theories of
earth pressure on retaining walls, and
the natural angle of response at which
a soil mass would remain stable, as
enunciated by C.A. Couloumb in
1776 and W.J.M. Rankine in 1856.
However, because of their simplified
assumptions on the behaviour of soil,
these theories had little practical use-
fulness outside of the classroom.
Humankind had been constructing
earth dams for at least 2,000 years
usually for the purpose of creating
water storage reservoirs. Yet the height
of such construction was limited to
about 100 feet before collapse. Dam
failures were widely reported in
the engineering literature, when the
mechanics of seepage, pore-water
pressure, and piping in cohesive soils
were still undiscovered. Few engineers
had the perspicacity of Samuel Fortier,
and systematic methods for compact-
ing the soils used to construct the dam
remained undeveloped.
Early in the 20th century, three major
engineering failures precipitated the
first modem soil studies. These were
the great landslides in the deep cuts
made to bring the Panama Canal
through the Continental Divide, the
catastrophic slides on the Swedish
state railways, and the outward move-
ments of the massive pile-supported
quay walls in the construction of the
COMMEMORATIVE EDITION
