Abstract:
A senes of laboratory tests was performed on specially prepared specimen of clay soil in
undisturbed, reconstituted and compacted conditions to study the stress and defol111ation
anisotropy. Clay soils in both undisturbed and disturbed conditions were collected from selected
locations of Dhaka City. For compacted soil specimen the collected soil sample was dried,
grinded and thcn compacted in laboratory with water content near to optimum moisturc content.
The compacted soil cake was extruded from the compaction mold and specimcns were prepared
for strength and defonnation tests. The tests were also done on undisturbed and reconstituted
soil samples having water content approximately to saturation. For reconstituted soil samples, a
soil SllllTYwas prepared at water content 1.25 times to liquid limit and consolidated at at Kocondition.
The undisturbed soil sample was taken using block sampling.
The test specimens were taken from soil masses at different orientations relative to its
depositional/consolidation direction. The major principal stress direction, compared to the
depositional/consolidation direction, was varied from 0= 0° (i.e., a vertical sample) to the
maximum 0= 90° (i.e., a horizontal sample). Similarly, test samples were also collected from a
horizontal plane (i.e., from a 0= 90° plane) by changing its orientation in that plane from a= 0°
(an arbitrarily choscn reference direction) to a= 180°. Test samples were subjected to undrained
strength tests, such as unconfined compression, direct shear tests and triaxial tests. Onedimensional
consolidation tests were also performed to evaluate defom1ation characteristics.
The existence of strength anisotropy was noticeable in compacted clays. The coefficient
of anisotropy, defined as the ratio of strength of vertical specimen to that of a horizontal
specimen, was varied from 0.75 to 1.25 in unconfined compression and unconsolidated direct
shear tests, while it was between 0.6 and 1.08 unconsolidated direct shear tests on soaked
samples. Compaction effort had influences on anisotropy, which was found to be dependent on
tcst types.
The strength of reconstituted and field clays was approximately isotropic in horizontal
plane. The strength was, however, anisotropic for specimens trimmed from a vertical plane at
different oricntations. The coefficient of anisotropy was mostly to that in compacted clays.
However, thc coefficient for undisturbed clay was varied between 1.01 (i.e., isotropic) to 1.55
(i.e., anisotropic).
Deformation characteristics (Ce, C, and my) and coefficient of pem1eability obtained by one dimcnsional
consolidation tests on reconstituted clay were directionally independent in a vertical
plane. Natural clay was, however, anisotropic both in deformation and hydraulic characteristics.
Keywords: anisotropy. clay, laboratory tests, reconstituted, field-undisturbed. strength and
deformation.
