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EFFECTS OF STRESS ROTATION AND CHANGES OF b-VALUES
ON CROSS-ANISOTROPIC BEHAVIOR OF NATURAL, K0-CONSOLIDATED
SOFT CLAY
POUL V. LADE and MARK M. KIRKGARD
ABSTRACT: A series of consolidated-undrained torsion shear tests was
performed on large, hollow cylindrical specimens of undisturbed San Francisco
Bay Mud to investigate the influence of stress rotation and changes in b-values
on the stress-strain, pore pressure, and strength characteristics of a cross-anisotropic,
natural clay. The specimens were first Ko-consolidated and then
sheared along various undrained stress paths to study the clay behavior in the
full range of stress rotation from 0°to 90° relative to vertical. For
this cross-anisotropic clay, the test results indicate that the major principal
strain increment directions in physical space do not coincide with the directions
of major principal stress at failure. The deviation between these two directions
varied continuously and the maximum deviation was measured at approximately 20°
, The normalized, undrained shear strength decreases systematically with inclination
of the major principal stress at failure,‚™",
from triaxial compression with‚™"=0°
and b=0 to triaxial extension with =90°and b= 1. The effective friction
angle remains constant at approx. 35° in the range of ‚™"from
0° to 30° after which increases gradually to almost 50° at ‚™"=
90°. These results are unlike those obtained for a laboratory prepared deposit
of kaolin, which tended to behave more like an isotropic material despite the
initial Ko-consolidation. Thus, effects of aging are very important
in the behavior of clays, and it may not be possible to simulate such effects
with sufficient accuracy and reliability with laboratory prepared clay deposits.
Key words: anisotropy, clay, consolidated undrained, shear,
cross-anisotropic, failure, shear-strength, torsion (IGC:
D6)
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