## 3 Results
### Characteristics of Shear Band  
#### 3.2.1 Evolution of Shear Bands  
To investigate the evolution of the shear band of specimens, a series of photographs was captured during plane strain compression tests for specimens consolidated to 100, 300, and 500 kPa. When the localized shear band develops into an evident shear band, and the stress-strain relationship is at a steady stage after the peak deviatoric stress, the shear band is considered as fully developed. DIC analyses were carried out for the T1, T3, and T5 tests at seven typical moments before the peak, at the peak, after the peak, and at the steady stage of the deviatoric stress, respectively. The local strain distributions were computed by comparing an image with its initial image, and the images of the strain fields at the seven moments were distinguished by the value of the global axial strain \(\varepsilon_{z}\). The results of the local equivalent strain (\(\varepsilon_{eq}\)) distribution and stress-strain relationship for the T1, T3, and T5 tests are shown in Figures 7-9. For the T1 test, the global stress-strain curve and the distribution of \(\varepsilon_{eq}\) calculated using the DIC technique are shown in Figure 7a,b, respectively. The image of \(\varepsilon_{eq}=0.64\%\) indicates no significant strain localization, as the local strain is relatively uniform in the specimen. However, in plane strain compression tests of the other natural clays [19; 26], evident strain localization appears at \(\varepsilon_{z}=3\)-5%. In other words, compared with the other natural clay, conspicuous strain localization appears at a small axial strain in Zhanjiang clay. The peak deviatoric stress is reached when \(\varepsilon_{z}=1.04\%\); however, the fully developed shear band does not appear in the specimen. The maximum \(\varepsilon_{eq}\) at this time is 2.67%, and strain localization appears only at the lower right corner of the specimen. When \(\varepsilon\) increases from 1.53% to 2.75%, accompanied by severe strain-softening, a band zone with localized shear strain (localized shear band) extends to the upper left of the specimen and gradually develops into a curved shear band. When \(\varepsilon_{z}\) increases from 2.75% to 8.45%, the stress-strain relationship is in a steady stage after the peak deviatoric stress, and the thickness of the shear band increases with increasing \(\varepsilon_{z}\). The maximum \(\varepsilon_{eq}\) inside the shear band exceeds  
Figure 7: Results of DIC analyses for the T1 test: (**a**) global stress–strain relationship for the T1 test; (**b**) shear strain distribution at different stages in the T1 test. 35% at \(\varepsilon_{2}\) = 8.45%. When the specimen failed, the specimen was divided into two parts by the shear band. Figure 8: Results of DIC analyses for the T3 test: (**a**) global stress–strain relationship for the T3 test; (**b**) shear strain distribution at different stages in the T3 test. Figure 9: Results of DIC analyses for the T5 test: (**a**) global stress–strain relationship for the T5 test; (**b**) shear strain distribution at different stages in the T5 test. For the T3 test, as shown in Figure 8b, unlike the T1 test, two conjugated localized shear bands appear when \(\varepsilon_{z}=1.55\%\). As the axial strain increases, the thickness of both localized shear bands increases accordingly. However, \(\varepsilon_{eq}\) in the localized shear band that inclined to the left increases faster than \(\varepsilon_{eq}\) in the localized shear band that inclined to the right after the peak deviatoric stress. When \(\varepsilon_{z}=5.05\%\), the maximum values of \(\varepsilon_{eq}\) in the localized shear band that inclined to the left and right are 26.36% and 14.52%, respectively. When \(\varepsilon_{z}=7.75\%\), the maximum value of \(\varepsilon_{eq}\) in the localized shear band that inclined to the left exceeds 35.0%, and the shear band that inclined to the left develops into a shear band.