Effect of qh on Shear Properties
Figure 10(a) shows the stress-strain relationships at αh = αs = 45o, bh = bs = 0.5, p' = 100kPa and various values of qh during the shear history process. As the deviator stress qh increases, the deviator stress q , which can maintain linearity, increases in turn.
Figure 10(b) shows the volumetric strain-shear strain relationships taking into account the drained shear process where αh = αs = 45o, bh = bs = 0.5, p' = 100kPa and various values of qh during the shear history process. It can be seen from the figures that when the deviator stress qh is smaller, there is more contractive volumetric strain. The results of these experiments lead to the conclusion that the magnitude of qh has an effect on the dilatancy characteristics of cohesive soil similar to shear deformation.
Effect of αh on Shear Properties
Figure 11(a) shows the stress-strain relationships taking into account the drained shear process where αs = 45o, qh = 60kPa, p' = 100kPa and different values of αh during the shear history process. The p' values during the shear history and during the shear process are both equal to 1 in these tests. When αh is coincident with αs (i.e., α of the shear history process is equal to 45o), the linear part before yielding maintains the largest deviator stress q . As the difference between αh and αs increases, the deviator stress q , which can maintain linearity during the drained shear process, decreases.
Figure 11(b) shows the volumetric strain-shear strain relationships for the same case illustrated in Fig. 11(a). Contractive volumetric strain occurs in all cases. Where the difference between αh and αs is larger, a more contractive response can be observed.
Figures 12 and 13 show the results for the same type of experiments as in Fig. 11 except for the value of b . The shear history in the tests shown in Fig. 12 and 13 was carried out under bh = 0.5 and bh = 0 conditions, respectively. A similar tendency to the case shown in Fig. 11 is indicated in the results of different cases which are shown in Fig. 12 (bs = 0.5) and Fig. 13 (bs = 0). These results imply that the elastic limit progresses sufficiently in the same direction as the shear history but progresses little at right angles to the shear history.
Effect of bh on Shear Properties
Figure 14(a) shows the stress-strain relationships of bs = 1 where αs = 45o, qh = 60kPa, p' = 100kPa and different values of bh. The yield points are a little different at various values of bh , and when bh is coincident with bs , the linear part before yielding maintains the largest deviator stress q . Where the difference between bh and bs is larger, the deviator stress q , which can maintain the linearity during the drained shear process, is smaller.
The relationships of εv - εs in the same case as shown in Fig. 14(a), are shown in Fig. 14(b). These relationships have a similar tendency to those in the stress-strain relationships. That is, where the difference of b between the shear history and the shear process increases, more contractive volumetric strain occurs.
A similar tendency is indicated in the results of different bs conditions which are shown in Fig. 15 (bs = 0.5) and Fig. 16 (bs = 0). It is interesting that the stress-strain and the volumetric strain-shear strain relationships of TH-21 and TH-24 are the same in Fig. 15, and that the differences in the values of b between the shear history and the shear are 0.5 for both TH-21 and TH-24. It is apparent from Figs. 14, 15 and 16 that the strength under constant p' is not affected by this type of stress history.
Interaction between αh and bh in Shear Properties
The effect of αh on shear properties was examined above based on the same b between the shear history and the shear. In this section, the effect of αh on shear properties was estimated based on the difference in b between the shear history and the shear.
Figures 17 and 18 show the shear properties for αs = 45o, bs = 1 and qh = 60kPa considering the effects of αh under conditions in which the differences in b between the shear history and the shear are equal to 0.5 and 1, respectively. By comparing Fig. 11, 17 and 18, it can be clearly seen that as the difference in the value of b between the shear history and the shear process increases, the effect of αh on shear properties decreases. These results can be inferred from the reduction of the linear section induced by the difference in b between the shear history and the shear process.
The effect of bh on shear properties was examined above based on the same α between the shear history and the shear. The effect of bh on shear properties was estimated below, based on the difference in α between the shear history and the shear.
Figures 19 and 20 show the shear properties for αs = 45o, bs = 1 and qh = 60kPa considering the effect of bh where the differences in α between the shear history and the shear are equal to 22.5o and 45o, respectively. By comparing Figs. 14, 19 and 20, it is evident that where the difference in the value of α between the shear history and the shear process increases, the effect of bh on shear properties decreases. These results can also be inferred from the reduction of the linear section induced by the difference of α between the shear history and the shear process.
This means that the shear properties are affected by the interaction between αh and bh , and the differences in α and b between the shear history and the shear seem to have a significant effect on shear properties.
Effect of Shear History on Strength
It is evident from the above-mentioned results that the stress-strain relationships of specimens subjected to the shear history get closer to those of the virgin shear as the shear strain increases, though the shear strain levels are small (εs = 4%). The results of comparatively large strain levels are shown in Fig. 21. It is clear from this figure that a satisfactory convergence in the deviator stress can be accomplished at an even larger strain. This implies that the shear history under constant p' conditions does not affect the strength of the cohesive soil, but that the strength is fixed by p' and bs during the shear. It should be noted that this result, relating to the strength obtained from the cohesive soil with induced anisotropy, is different from that relating to sand with inherent anisotropy. For instance, Oda (1972) showed that the initial fabric of sand had a significant effect on the strength.
Non-coaxiality between Stress and Strain
It is possible to generate non-coaxiality between stress and strain when soils have anisotropic characteristics. The non-coaxiality generated by the shear history is investigated in this section by paying attention to the directions of major principal stress and strain.
The relationships between αε and εs relating to the effect of αh are shown in Fig. 22. The experiments were carried out under αs = 45o, bh = bs = 0.5 and qh = 60kPa. The data for αε at less than 0.02% shear strain might contain some significant errors. This means that the data from the very small strain is not reliable because it includes an unacceptable level of error. The gaps between α and αε hardly exist in the cases of the virgin shear, αs = 45o conditions and αs = -45o conditions. In other words, the non-coaxiality between stress and strain does not occur when the directions of the shear history and shear are coincident or are at right angles to each other. Moreover, the gap between α and αε looks largest in the case of α = 0o even if by a small margin. However, the direction of shear strain tends to converge in the direction of shear stress with shear strain. Although these are the results of bh = bs = 0.5, a similar tendency was observed in the case of bh = bs = 0 or bh = bs = 1.
The relationships between αε and εs relating to the effect of bh are shown in Fig. 23. The experiments were carried out under αh = αs = 45o, bs = 0.5 and qh = 60kPa. Although there are minor gaps in small strain, they promptly converge on αe = 45o. This fact indicates that the effect of bh on the non-coaxiality is not so important.
