Laboratory Simulation of Field Sampling: Comparison With Ideal Sampling and Field Data

Tube sampling disturbance effects are investigated in this paper based on the results of constant rate of strain consolidation tests and unconsolidated undrained triaxial compression tests conducted on resedimented Boston blue clay sampled in the laboratory using a specifically designed device and employing various tubes differing in size, diameter to thickness ratio, and tip geometry. The effects of tube geometry were assessed based on comparison of the residual effective stresses, the reconsolidation strains, the undrained strength, and the one-dimensional drained compression behavior. Increasing degradation in the engineering properties was observed with decreasing diameter to thickness ratio (B/t), and the negative impact of a blunt tip geometry could not be compensated for even by a substantial increase in B/t. Comparison of these results to those obtained from triaxial element tests in which disturbance was simulated according to the ideal sampling approach (ISA), indicated that tube sampling is associated with far greater disturbances than what is accounted for by the ISA. Further, additional comparisons with the results of tests run on actual field samples of low over consolidation ratio Boston blue clay from two sites in the Boston area indicate that the behavior observed in the laboratory sampled soil is generally representative of actual field data.