Sampling Disturbance Effects in Normally Consolidated Clays

The effects of sampling disturbance are investigated by performing single element triaxial tests in which specimens of normally consolidated resedimented Boston blue clay are disturbed according to the “perfect sampling approach” (PSA) and the “ideal sampling approach” (ISA). The effects of PSA and ISA disturbance on the compression and undrained shear behavior of the soil are quantified by comparison with the intact behavior. The results indicate that the release of shear stress associated with PSA disturbance causes a modest change in the engineering properties of the soil. The effects of ISA disturbance are, on the other hand, very significant and increase systematically with the amplitude of the strain imposed. An increase in disturbance causes a decrease in the compression ratio, a decrease in the undrained strength, and an increase in the strain at failure and the recompression ratio, but has a minor effect on the preconsolidation pressure. These effects derive from the decrease in effective stress and from the damage to the soil fabric that occur as a result of sampling. The loss in undrained strength is primarily controlled by the decrease in effective stress and the post-disturbance strength ratio (cu/σs′) may be related to the “induced” overconsolidation ratio (IOCR=σvc′/σs′) through a SHANSEP equation.