Experimental study on mechanical behavior of weakly structured soft clays

The oedometer and triaxial shear tests on undisturbed, remolded and reconstituted samples of two different weakly bonding soft clays are carried out to obtain the compression curves and stress-strain curves. The test results show that the compressibility abruptly increases in the compression curves of undisturbed samples, and the difference among compression curves of different samples is obvious. The strength is not only different for undisturbed and remolded samples for the difference in void ratio, but also different for samples with the close void ratio when they are sheared under the same confining pressures, because the strength of clay is affected by both void ratio and pore-size distribution. The undisturbed samples will have the highest strength and the remolded samples will have the lowest strength if they have the same void ratio, and it is valid for different soft clays used in the tests. The relation of strength among different samples can be explained reasonably by the volume of pore per unit soil volume with its diameter greater than 0.2 μm and the uniformity of pore-size distribution. Because the difference of the pore-size distribution curves among different samples cannot be eliminated by the increasing consolidation pressure, the reference void ratio e* 10, a parameter simply describing the void ratio and pore size distribution of soil (fabric) is introduced. The compression and shear test results of different samples dealt with by the reference void ratio e* 10 show that they can be normalized to unique e/e* 10-σ_v and e_f/e* 10-q_f curves with high correlation. The normalized results show that if the stress is larger than the structures yield stress, the difference in compression and shear characteristics among the samples are caused by the void ratio and pore-size distribution (fabric), and it can be simply and usefully described by the reference void ratio e* 10.