*Article* **Experimental Study on the Shear Strength of Silt Treated by Xanthan Gum during the Wetting Process**

**Junran Zhang \*, Zhihao Meng, Tong Jiang, Shaokai Wang, Jindi Zhao and Xinxin Zhao**

Henan Province Key Laboratory of Geomechanics and Structural Engineering, North China University of Water Resources and Electric Power, Zhengzhou 450045, China; z20201020288@stu.ncwu.edu.cn (Z.M.); jiangtong@ncwu.edu.cn (T.J.); wangshaokai@ncwu.edu.cn (S.W.); x201810207162@stu.ncwu.edu.cn (J.Z.); zhaoxinxinncwu@126.com (X.Z.)

**\*** Correspondence: zhangjunran@ncwu.edu.cn; Tel.: +86-15890092736

**Abstract:** Traditional materials such as fly ash and lime are generally used to improve soils but can severely pollute the environment. Eco-friendly protocols, such as the application of xanthan gum, are therefore essential for soil treatment. In this study, a series of microscopic tests, water retention characteristics tests, and shear tests were carried out on silt, which are known to have poor engineering properties, to explore the effect and mechanism of xanthan gum treatment on the water retention and shear strength characteristics of silt during the wetting process. The results show that the water retention capacity of the treated silt increases with increasing xanthan gum content, and a hysteresis effect is clearly observed. The cohesion and internal friction angle of the silt strongly decrease with increasing water content, and the strength significantly weakens. However, the strength of the silt treated with xanthan gum is consistently higher than that of the untreated silt. The microscopic tests show that soil pores are gradually filled by xanthan gum with good water-retaining properties, thus significantly enhancing the water retention capacity. Furthermore, the hydrogel that cements the soil particles forms by the bonding effects between xanthan gum and soil particles, which greatly improves the silt strength.

**Keywords:** xanthan gum; silt; water retention capacity; strength; wetting process; microscopic tests
