Abstract:
The undrained behaviour of sands is
affected by many factors including the initial
state and loading path. If laboratory studies are
to be meaningful in the context of in-situ
problems, both the initial state and subsequent
loading path in-situ have to be appropriately
simulated in the laboratory. This is critical since
most natural soils have an anisotropic (or
technically a transversely isotropic) fabric and
their response is direction dependent. The term
initial state encompasses the density, fabric of
the soil, and the stress conditions which are
characterized by the three principal stresses and
their directions. This paper summarizes the
impact of anisotropic fabric on both monotonic
and cyclic undrained behaviour of sands.
The anisotropic response that is manifested in
simpler triaxial compression and extension tests
and is systematically studied using a relatively
complex hollow cylinder torsional shear device.
It is shown that the tendency for strain softening,
which could lead to catastrophic consequences
under monotonic loading, is very much
dependent of fabric and loading path. It is
demonstrated that current cyclic liquefaction
design practice that depends on the cyclic
resistance ratio, CRR is rather simplistic, but the
available data suggests that cyclic simple shear
resistance is possibly a lower bound for the
actual resistance.
The data and experience presented in this
paper suggest that the difficulties encountered in
using laboratory test results in field problems
are possibly a result of inappropriate laboratory
characterization without regard to the initial
fabric and the subsequent loading paths in-situ.
