Characterisation of the mechanical behaviour of layered clay sedimented using a geotechnical centrifuge

Ritchie (2023) describes how Speswhite Kaolin and Polwhite E Kaolin can be combined at very high water contents to create a slurry from which a series of layers of clay can be sedimented in a soil container using a geotechnical centrifuge. Because Polwhite E Kaolin has a larger particle size than Speswhite Kaolin the Polwhite E Kaolin sediments first, creating a higher permeability deposit at the base of each sedimented layer. This bed of sedimented layers of clay can then be consolidated in a consolidation press to reach states allowing the construction of a reduced scale physical model of, for example a tunnel excavation, which can be tested in the centrifuge. The paper presents results of preliminary triaxial tests characterising the strength and volumetric compression of this laboratory sedimented clay. In addition, these data are compared to data from specimens of clay where the Speswhite Kaolin and Polwhite E Kaolin have been mixed evenly or reconstituted at water contents of approximately 120%, allowing the effect of the sedimented structure to be quantified with respect to an equivalent reconstituted soil as is frequently undertaken when studying natural sedimented clays. The preliminary data presented indicates that the sedimented clay has a stable structure or fabric which only affects the specific volume or packing of the soil grains at a given value of mean effective stress. The sensitivity of the sedimented clay when compared to the same clay reconstituted is as much as 4.7. The angle of friction or coefficient of friction of the sedimented clay appears to be very similar to that of the reconstituted clay.