Stress–strain responses of reconstituted and natural compressible Chicago glacial clay

Reconstituted clay specimens with same stress history are often used to characterize natural samples due to their minimal variability and the reduced impact of sampling disturbance. The use of reconstituted samples is very effective particularly at sites with uniform geologic formation. This paper compares the results and analysis of a laboratory investigation of the very small, small and large strain behaviors of reconstituted and natural Chicago clay. Reconstituted specimens were cut from blocks derived from the slurry consolidation of dried natural Chicago glacial clays. Index properties and results of axially-oriented bender element tests and drained stress probe tests and oedometer tests were compared with data for natural specimens. Even though both sample types share similar index properties, 1D consolidation characteristics and failure lines, softer responses of reconstituted samples are observed in terms of initial shear moduli, shear, bulk and coupled responses and local yielding surface. The differences in those quantities of the two sample types are neither uniform nor proportional with strain levels. The developed structures due to the longer ageing period of natural samples are clearly shown in terms of residual effective stress ratios, shear wave velocity and deformation parameters including coupling between shear and volumetric responses. Thus, the small strain response of natural compressible Chicago glacial clay cannot be simply quantified via reconstituting process presented herein.

► Natural and reconstituted clays had similar index properties and stress histories.
► GBE of the reconstituted clays were about 20% lower than those of natural ones.
► Reconstituted clays show smaller secant shear and bulk moduli than natural ones.
► Though the local yield surface of reconstituted clay is smaller than that of natural ones.
► Reconstituted clays cannot be used instead of natural Chicago clays.