The application of critical state framework depends on the presence of either a unique critical state line (CSL). However, many authors have observed that a transitional behaviour occurs in certain granular intermediate soils in which the fines content and the initial void ratio have a significant effect on the location of this line. This work investigates these effects in poorly graded granular soils as previous studies reported that this type of soil does not exhibit transitional behaviour. Results from this study reveal that poorly graded fine-grained sand exhibits transitional behaviour similar to that of intermediate soils, and subsequently, it can be grouped into ranges of initial densities in which each group approaches a unique CSL in v:lnp' space. A unique state boundary surface is identified by determining the critical state parameters from each group and using these parameters to normalise the stress paths; this shows that the critical state framework can be successfully applied to this type of soil.