3.4.2. Strength Characteristics of Xanthan Gum-Treated Silt

Figure 16 shows the shear strength–displacement relation curves of the XG-silt samples with different water content. The peak strength and residual strength of the treated silt were found to gradually increase with the increase in vertical stress.

**Figure 16.** Shear strength of xanthan gum-treated silt with different water contents (*mbp*/*ms* = 2%): (**a**) *w* = 2%; (**b**) *w* = 4%; (**c**) *w* = 8%; (**d**) *w* = 16%; (**e**) *w* = 22%.

When the water content was 2%, 4%, and 8%, the shear strength–displacement relation curves of the treated silt showed the stress-softening phenomenon. When the water content was 22%, the shear strength–displacement relation curves of the treated silt showed a stress-hardening phenomenon. When the water content was 16%, and the vertical pressure was 50 kPa, the shear strength–displacement relation curve of pure silt showed a stresssoftening phenomenon, and when the vertical stress was 100 kPa and 200 kPa, shear strength–displacement relation curves showed a stress-hardening phenomenon.

Figure 16c,d show the stress softening into stress hardening with water content increasing from 8% to 16% after the addition of XG.

## 3.4.3. Relationship between Strength and Water Content

Figure 17 shows the shear strength–displacement relation curves of the pure silt and XG-silt specimens with different water contents under vertical stress of 100 kPa. The strength of the silt specimens gradually increased with decreasing water content, as did the strength of the XG-silt specimens.
