Strength and deformation anisotropy of clays

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.