# Study on the Development Rule of Mudstone Cracks in Open-Pit Mine Dumps Improved with Xanthan Gum
## 4 Discussion
### Modification Mechanism  
Based on the XRD analysis results, it is known that the open-pit mine mudstone contains a portion of clay particles (kaolinite, illite, and montmorillonite), accounting  
Figure 9: Comparison of microscopic images under scanning electron microscope. (**a**) 500x U1 specimen SEM image; (**b**) 1.0 kx U1 specimen SEM image; (**c**) 2.0 kx U1 specimen SEM image; (**d**) 5.0 kx U1 specimen SEM image; (**e**) 500x M6 specimen SEM image; (**f**) 1.0 kx M6 specimen SEM image; (**g**) 2.0 kx M6 specimen SEM image; (**h**) 5.0 kx M6 specimen SEM image; (**g**) 2.0 kx M6 specimen SEM image; (**h**) 5.0 kx M6 specimen SEM image. for 31.4%. Negatively charged clay particles form an electric field around them, and surrounding water molecule dipoles, cations, etc., are adsorbed on the surface due to electrostatic attraction [36]. XG is an anionic polysaccharide composed of D-glucuron acid, D-mannose, pyruvate mannose, 6-O-acetyl D-mannose, and 1,4-linked glucan. The primary chemical structure of xanthan gum is a linearly linked \(\beta\)-D glucose backbone with a trisaccharide side chain on every other glucose [37]. As shown in Figure 10a, due to the presence of a large number of carboxyl (-COOH) groups and hydroxyl (-OH) groups in the chemical structure of XG, under conditions of sufficient moisture, these anionic groups can form bonds with cations, oxygen atoms, and water molecules on the mineral surface. This bonding can enhance the inter-particle linkage force and resist the tension of drying shrinkage in the form of bond energy during drying and water loss [38]. In addition, under static conditions, a small amount of XG can cause a significant increase in the viscosity of liquids. While adding water for wetting, XG dissolves in water to form a gelatinous liquid with a specific viscosity, filling the gaps between the soil particles. It shrinks during drying and water loss and becomes a hard plastic-like substance. XG gradually shrinks and accumulates during the drying and curing process, merging into bridge links to form a dense network that tightly connects the framework of adjacent soil bodies [39]. Therefore, in the electron microscope image of the unmodified U1 specimen, the soil particles are dispersedly arranged with many pores. In contrast, in the M6 specimen with added XG, they appear dense and reticulated. Based on the analysis above, we can summarize the mechanism by which xanthan gum (XG) modifies the properties of mudstone in open-pit mines. When the specimen is in a water-saturated state, the XG solution can effectively carry fine particulate matter, which then extends and fills into the pores of larger mudstone particles. Electrostatic bonding and hydrogen bonding allow the fine particles in the XG solution to firmly adhere to the surface of the soil. As the drying process progresses, the water in the XG gradually evaporates, causing some soil particles to detach from the adsorption on the surface of the larger mudstone. At the same time, other soil particles interact with the XG matrix during the drying shrinkage process, forming a filamentous network structure. These filamentous networks act to connect and fill between the mudstone bodies, enhancing the overall structural stability of the soil. The entire process is depicted in Figure 10b. During the wet-dry cycling process, XG continuously transitions between a gel-like solution and a filamentous matrix. This transition is crucial for maintaining the stability and strength of the soil. Due to XG's inherent stability and durability, its performance does not show a significant decline even after six wet-dry cycles. This indicates that mudstone modified with XG can maintain good performance under repeated changes in moisture conditions, which is of great significance for improving the engineering performance of mudstone in open-pit mines.