In May 1970, a 70 ft tall, 20 ft diameter concrete grain silo was constructed at a site in EasternCanada (Bozozuk, 1972b). This cylindrical silo, which had a weight of 183 tons, was supportedon a 3 ft wide, 4 ft deep ring foundation. The outside diameter of this foundation was 23.6 ft,and its weight was about 54 tons. There was no structural floor (in other words, the contents ofthe silo rested directly on the ground).The silo was then filled with grain. The exact weight of this grain is not known, but wasprobably about 533 tons. Unfortunately, the silo collapsed on September 30, 1970 as a resultof a bearing capacity failure.The soils beneath the silo are primarily marine silty clays. Using an average undrainedshear strength of 500 lb/ft2 , a unit weight of 80 lb/ft3 , and a groundwater table 2 ft below the ground surface, compute the ASD factor of safety against a bearing capacity failure, then com-ment on the accuracy of the analysis, considering the fact that a failure did occur.
In May 1970, a 70 ft tall, 20 ft diameter concrete grain silo was constructed at a site in Eastern
Canada (Bozozuk, 1972b). This cylindrical silo, which had a weight of 183 tons, was supported
on a 3 ft wide, 4 ft deep ring foundation. The outside diameter of this foundation was 23.6 ft,
and its weight was about 54 tons. There was no structural floor (in other words, the contents of
the silo rested directly on the ground).
The silo was then filled with grain. The exact weight of this grain is not known, but was
probably about 533 tons. Unfortunately, the silo collapsed on September 30, 1970 as a result
of a bearing capacity failure.
The soils beneath the silo are primarily marine silty clays. Using an average undrained
shear strength of 500 lb/ft2
, a unit weight of 80 lb/ft3
, and a groundwater table 2 ft below the
ground surface, compute the ASD factor of safety against a bearing capacity failure, then com-
ment on the accuracy of the analysis, considering the fact that a failure did occur.
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