*2.1. Materials*

Figure 1 shows that Henan Province is located in the North China Plain of the middle and lower reaches of the Yellow River, where silt is widely distributed. The silt sample location is at an engineering project in the Xing-yang area, west of Zhengzhou city in northern Henan Province, which adjoins the south bank of the Yellow River. The experimental alluvial silt has poor early strength and water stability [40,41]. Xanthan gum is therefore used to strengthen the silt in the Yellow River flooding area due to the complex engineering properties of silt.

Xanthan gum is a high molecular anionic polysaccharide polymer produced by the aerobic fermentation of Xanthomonas and carbohydrates. It is carbon neutral, sustainable and reproducible, stable to acid, alkali, and heat, and has excellent compatibility with a variety of salts. It is made from non-food crops at a low cost and can be prepared in large quantities [26]. The xanthan gum used to treat the silt was purchased from Fu Feng Biotechnology Co., Ltd. in Inner Mongolia. The reagent was of food grade and analytical grade. The storage environment conditions were 25 ◦C and 35% relative humidity. Pictures of the dry silt and xanthan gum are shown in Figure 2.

**Figure 2.** Samples of natural soil and xanthan gum: (**a**) silt; (**b**) xanthan gum.

The basic physical properties of natural silt are listed in Table 1. The grading curve determined by hydrometer analyses is shown in Figure 3. The gradation parameters of the soil sample are coefficient of curvature *C*<sup>c</sup> = 0.75, nonuniform coefficient *C*<sup>u</sup> = 4.39, and liquid limit *w*<sup>l</sup> = 21.4%, and the silt shows poor gradation with a low liquid limit.

**Table 1.** Basic physical properties of silt.


**Figure 3.** Grading curve of the silt.

The basic parameters of xanthan gum (XG) are shown in Table 2, and its molecular structure is shown in Figure 4.


**Table 2.** Basic physical properties of xanthan gum.

**Figure 4.** Molecular structure of xanthan gum.
