Disturbances due to Tube Sampling in Coastal Soils

The effects of tube sampling disturbances on undrained shear characteristics of reconstituted samples of three coastal soils were investigated. The values of undrained shear strength su and initial tangent modulus Ei were reduced, whereas axial strain at peak deviator stress (epsilon)p increased because of a disturbance caused by penetration of samplers. Disturbances also reduced initial effective stress (sigma)ʹi and pore pressure changes considerably. The changes in soil parameters between the "in situ" and "tube" samples depended markedly on the geometry of samplers used to retrieve tube samples. Values of su, Ei, and (sigma)ʹi of samples were reduced, whereas the values of (epsilon)p increased with an increasing area ratio (or decreasing external diameter to thickness ratio) and an increasing outside cutting edge angle of the samplers. Different reconsolidation procedures were adopted to assess the suitability of reconsolidation of tube samples to recover in situ properties. It was found that the K0-reconsolidation of tube samples to vertical effective stresses equal to 1.5 and 2.5 times the in situ vertical effective stress produced the best overall estimate of in situ characteristics.