The
LIQUITER program determines the safety factors pertaining to the
liquefaction of incoherent saturated terrains subjected to earthquake
phenomena.
The
used calculation method, proposed by Seed and Idriss in 1982, is
the best known and most frequently used as it requires the knowledge
of only a few and commonly used geotechnical parameters(volume weight,
relative density and the mean particle diameter).
Like
all methods based on the concept of resistance factors, it is necessary
to evaluate the resistance of the soil to the cyclic shear stresses:
the program uses the correlation between the resistance to liquefaction
and the number of blows of the SPT test.
The
last input value required by the program is the definition of the
seismic parameters that are necessary to simulate the earthquake.
The
used formula enables one to take into account the sporadic character
of the maximum acceleration peaks through the ratio of cyclical
stress induced by the earthquake with reference to a mean value
instead of the maximum value.
For
each SPT test that is carried outs, the corrected number of blows
is calculated in such a way as to consider the lithostatic pressure,
through the use of a corrective coefficient that is a function of
the depth where the test is performed and the relative density.
It
is also possible to consider the presence of a load and take the
layers of soil above the aquifer, considered as loads acting on
the underlying terrain, into account.
The
verification is based on the determination of the resistance to
liquefaction factor witch is calculated as the ratio between the
limit shear stress that induces liquefaction and the maximum shear
stress induced by the earth quake, but leaving out the interstitial
pressures and deformations that develop during the earthquake.
