| Summary: | A one dimensional incremental effective stress liquefaction model is presented. Two
versions of the model have been developed - a static model to simulate the behaviour of a
sand element to laboratory cyclic simple shear tests, and a dynamic model to compute the
response of sand under harmonic or earthquake loading. For undrained cyclic loading,
neither model incorporates strain softening response typical for loose sands, but have been
calibrated to predict the response type known as cyclic mobility.
The static version of the model is calibrated to match characteristic laboratory cyclic
simple shear test results. Comparisons between laboratory results and modelled data are
presented.
The dynamic version of the model incorporates the key components of the static
model, and can be used to predict the response of a simplified soil profile under dynamic
loading. In particular, earthquake acceleration time history records may be used as input.
The dynamic model was applied to simulate the field case history recorded at the
Wildlife Site in California during the 1987 Superstition Hills earthquake. The recorded
downhole acceleration time history was used as input for the dynamic model and the
predicted response, in terms of surface acceleration, relative displacement, and porewater
pressure, compared with the measured values.
The predicted acceleration and displacement time histories are in good agreement with
the measured values in terms of both the amplitude and characteristic frequency of response.
The predicted porewater pressures are not in good agreement with the recorded
values. The predicted porewater pressure rise is much faster than the measured data. The
slower response may be due to limitations in the compliance of the measuring system and to
the possibility that liquefaction did not occur simultaneously at all points in the liquefied
layer.
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