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Dynamic impedances of
pile groups |
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 When
the natural soil is unable to provide the necessary stiffness
or strength under the design loads, a pile foundation may be
required. The study of the response of pile groups may be complex,
particularly under dynamic loads (earthquakes, ship impact,
winds, etc). In dense pile groups, the interaction between neighbouring
piles via the intervening soil has important effects on the
dynamics of the group.
 Principia
uses special purpose software for evaluating the dynamic impedances
of dense pile groups, a methodology that the company has applied
in many projects of high responsibility: nuclear power plants,
liquefied natural gas tanks, large bridges, petrochemical plants,
etc.
The photographs correspond to the pile foundation of two large
LNG tanks in India, designed by Principia in collaboration with
Esteyco.
Each tank is supported on 578 concrete piles, 1 m in diameter
and about 40 m long. |
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Failure of the Aznalcóllar
tailings pond |
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The infamous failure of the Aznalcóllar
tailings pond in April 1998 was analysed by Principia for
Boliden Apirsa, owner of the facility, in order to identify
the causes of the accident. The studies showed that failure
occurred because the design did not account for the slow consolidation
of the underlying blue clays and the brittleness of their
structural behaviour.
The detailed simulation of the failure process is particularly
difficult in this case. It requires conducting coupled calculations,
using effective stresses in the soil, along the construction
period, as well as an explicit representation of the softening
response that the brittleness of the clays entails. Further,
the onset of failure produces tailings liquefaction and a
sudden acceleration of events; the dam moved up to 60 m along
hundreds of metres of its length.
The first figure shows the calculated failure mechanism,
which is consistent with the one actually experienced. The
second one is a photograph of the pond taken after the accident. |
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