The phenomenon of soil dilatancy is the key to the characterising the strength and deformation of soils. The best known are the Rowe [10, 11] and Bolton  stress–dilatancy relationships for granular soils. Similarly, the dilatancy equations of Cam-clay and Modified Cam-clay  models are known for remoulded and normally consolidated clay. For structured and highly overconsolidated clays, however, the Cam-clay model’s stress–dilatancy relationships should be modified. By differentiating the plastic potential functions of the classical elasto-plastic model, various stress–plastic dilatancy relationships can be obtained . Szypcio  developed a general stress–plastic dilatancy relationship for soils based on the Frictional State Concept (FSC). The linear general stress–plastic dilatancy relationship defined by the critical frictional state angle (
In this paper, the stress–plastic dilatancy behaviour of Fujinomori clay during drained triaxial tests will be analysed. Data from drained TXC and TXE tests conducted by Nakai and Hinokio  with various OCRs and different stress paths conducted by Nakai and Matsuoka  will be taken for analysis. The influence of OCR and stress path on the stress–plastic dilatancy behaviour will be presented.
The general stress ratio–plastic dilatancy equation of the FSC  is
For drained TXC,
For drained TXE,
For TXC and TXE,
For drained TXC, the dilatancy equation of the Cam-clay model is 
The results of drained triaxial tests of Fujinomori clay conducted by Nakai and Hinokio  and Nakai and Matsuoka  will be analysed. Specimens for tests were prepared by mixing natural Fujinomori clay (
The samples prepared in this way were consolidated isotropically to the pressure
High-degree polynomials were used to segmentally approximate the relationships
The behaviour of the remoulded Fujinomori clay under different OCRs during drained TXC is shown in Figure 1. On the basis of the experimental results  of the relationship between the stress ratio and the shear strain (Fig. 1a) and of the volumetric strain and the shear strain (Fig. 1b), the relationship between the stress ratio and plastic dilatancy was calculated (Fig. 1c).
The behaviour of clay during shear is highly dependent on OCR. For OCR = 1 and 2, contractive behaviour and for OCR = 4 and 8, dilative behaviour are observed. In all tests, plastic strains (
The behaviour of Fujinomori clay in the drained TXE tests is shown in Figure 2.
As in the case of TXC, the relationships
The influence of the stress path on the behaviour of remoulded Fujinomori clay in drained TXC and TXE was studied by Nakai and Matsuoka . The TXC and TXE tests were carried out for stress paths σ′3 - constant,
Linear approximations of the stress to plastic dilatancy ratio in different shearing stages are described by Equation (1) with the critical frictional state angle
OCR and stress path significantly influence the shearing behaviour of the remoulded clay.
The general dilatancy equation of FSC can be used to describe the behaviour of the stress–plastic dilatancy relationships of soils during shearing.
The Cam-clay model dilatancy equation describes well the stress–dilatancy behaviour only for remoulded, normally consolidated clay loaded under a constant mean pressure stress path.
DFS independent of OCR and stress paths are very characteristic states of soil behaviour during shear.
The points representing DFS lie on the friction state line defined in the
The relationships between stress and plastic dilatancy, although rarely presented in the literature, are important for a full understanding of the behaviour of clay during shearing.
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