In Fig. 8.5, the state of the sample at R1 where the stress is p
01 can move to R2 only by loading to the NCL at N1 where it yields at the yield stress p
y1, further compression along the NCL to N2 where the yield stress is p
y2 and unloading to R2 where the stress is p02. The state of a soil can however move directly from R1 to R2 by creep in fine-grained soils and vibration in coarse-grained soils. Moreover the position of the NCL can shift as a result of soil structure. These mechanisms will be described further in Chapter 16.