2.2.1. Sample Preparation

Soil samples were prepared following the dry method [42], which was commonly used in previous tests. The dried silt powder was fully mixed with dried xanthan gum. Water was then added, and the mixture was stirred evenly. Based on previous experimental studies, the optimal mass ratio (*mbp*/*ms*) of dried XG and dried silt in the water retention characteristics tests was set as 0.0%, 0.5%, 1.0%, 1.5%, and 2.0%, and the optimal mass ratio in the direct shear tests was set as 2.0% [21,33,34,43]. In order to ensure the uniformity of XG-silt, dry soil was stirred and mixed evenly with XG of the corresponding quality. Deionized water was added to form wet soil that avoids the influence of additional chemical components in the water. The soil was then sealed at a constant temperature for 24 h until the water was fully infiltrated. The initial water content of the specimen was 15%, and 92% of the maximum dry density, *ρ*<sup>d</sup> = 1.63 g/cm3, was selected as the initial dry density. After specimen preparation, a vacuum pump was used to vacuum and saturate the specimen for testing.
