SAMPLING DISTURBANCE EFFECTS IN RECONSTITUTED COASTAL SOILS

M. A. BASHAR, ABU SIDDIQUE and A. M. M. SAFIULLAH

ABSTRACT: The effects of tube sampling disturbances on undrained shear properties of reconstituted samples of coastal soils were investigated. The values of undrained shear strength (s_u), initial tangent modulus (E_i) and secant modulus (E₅₀) were reduced while axial strain at peak deviator stress (e_p) increased because of disturbance caused by the penetration of samplers. Disturbances also considerably reduced initial effective stress (s'_i) and pore pressure changes. The changes in soil parameters between the "in-situ" and "tube" samples depended markedly on the characteristics of the tube samplers. Values of s_u,E_i, E₅₀and s'_i decreased while the values of e_p, increased with increasing area ratio (or decreasing external diameter to thickness ratio) of the samplers. It was also found that the reductions in the values of s_u,E_i, E₅₀ and s'_i increased with decreasing plasticity of the soils. A number of reconsolidation procedures, both isotropic and anisotropic including SHANSEP methods, were adopted in order to assess the suitability of reconsolidation of "tube" samples to recover the "in-situ" properties of the soils. It appeared that reconsolidation using SHAN- SEP procedures may not be applicable to these coastal soils. However, K₀-reconsolidation to "in-situ" stresses provided a better estimate of "in-situ" properties than other reconsolidation techniques.

Key words: coastal soils, pore pressure, sample disturbance, shear strength, stiffness, strains, triaxial compression, tube sampler (IGC: C6/D6)