Experimental Study On Strain-Softening Behaviour Of Saturated Silty Sand

In this study, a series of isotropically consolidated undrained triaxial tests (CU) were conducted on a clean sand (S), silty sands with three different silt contents (FS1: with 10% silt content, FS2: with 20% silt content and FS3: with 30% silt content) and a silt (F) to investigate the effects of void ratio, confining pressure and silt content on the strain-softening behaviour (instability) of saturated silty sands. The forementioned behaviour was interpreted by the intergranular state parameter, which is derived from the framework of the equivalent intergranular void ratio and the critical state theory. The major findings of this study are as follows:(1) All the five tested materials exhibit the strain-softening behaviour (instability). The brittle index I_B and the stress ratio of instability line (IL), (q/p')_IL are used to quantify the degree of strain-softening and define the boundary of stress states beyond which strain-softening behaviour may occur, respectively. The void ratio (after consolidation) and the confining pressure are the key factors which affect their strain-softening behaviour.(2) For the same tested material consolidated to the same void ratio, I_B increases with confining pressure. (q/p')_IL decreases with increasing confining pressure, i.e. the area of the zone of instability (i.e. the area between IL and critical state line) increases with confining pressure. For the same tested material consolidated to the same confining pressure, I_B increases with void ratio. (q/p')_IL decreases with increasing void ratio, i.e. the area of the zone of instability increases with void ratio.(3) For silty sands possess silt contents smaller than 30% which are subjected to the same confining pressure and void ratio, (q/p')_IL decreases with increasing silt content, i.e. the area of the zone of instability increases with silt content. I_B increases with silt content.(4) It is assumed that some portions of silt only fill the void between large sand particles which do not take part in the load bearing of the global soil skeleton, thus it is postulated to use the equivalent intergranular void ratio (e_ge) to replace the void ratio to describe the strain-softening behaviour of the silty sands. If e_ge is used to interpret the critical states of the silty sands which possess silt contents smaller than 30%, the critical states of silty sands (FS1 and FS2) and clean sand(S) will be represented by the same critical state line (CSL) in e_ge-ln p' plane.(5) The intergranular state parameter (ipge) which is derived from the framework of the equivalent intergranular void ratio and the critical state theory was used to interpret the strain-softening behaviour of the silty sands which possess silt contents smaller than 30% (FS1 and FS2). (q/p')iL decreases linearly with increasing ijjge. Ib equals to zero when ipge is less than a threshold value beyond which Ib increases with...