## 1 Introduction
To evaluate the overall performance of biopolymer-soil mixtures, a series of tests are typically conducted, including measurements of soil compressive strength [23], shear strength [24; 25], and other related parameters. These experiments are crucial for understanding how biopolymers influence the physical and mechanical properties of soil [26], providing a scientific foundation for their practical application. Biopolymers, by binding soil particles, can significantly enhance the mechanical strength of the soil, improving its compressive and shear strengths. The soil modified with biopolymers retains moisture more effectively, reducing soil moisture loss. Biopolymers can effectively increase the soil's cohesion, reducing erosion caused by water flow. Biopolymers also help restore plant growth [22], providing support for ecosystem restoration. As biodegradable and environmentally friendly materials, biopolymers, when used to modify soil, do not cause long-term environmental pollution. The modification of granite residual soil with biopolymers not only enhances the stability and bearing capacity of the soil in geotechnical engineering [11] but also mitigates soil erosion and contributes to ecological restoration in environmental protection. The current solidification methods for granite residual soil mainly include chemical stabilizers and MICP technology. Biopolymers, which are natural polymer compounds derived from living organisms, can reduce environmental damage and pollution compared to chemical stabilizers. In comparison to MICP technology, biopolymers offer significant advantages in terms of solidification speed, adaptability, ease of construction, and resistance to harsh environmental conditions. Although existing studies have investigated the use of biopolymers in soil improvement [27, 28], research on their effectiveness and the microscopic mechanisms by which biopolymers enhance the strength of GRS remains limited. This study fills this gap in the field by focusing on the curing effects and mechanisms of biopolymers on granite residual soils. Compared to traditional homogeneous soils, granite residual soils have significant heterogeneity and differences in soil properties, making the study of biopolymer stabilization of these soils both theoretically and practically significant. Compared to existing stabilization solutions, the biopolymer stabilization method proposed in this study shows clear advantages in curing heterogeneous soils and provides a more competitive solution in terms of environmental friendliness and cost-effectiveness. Given this context, conducting an in-depth investigation into the application of biopolymers for stabilizing GRS is of considerable practical importance. In this study, three types of biopolymers-XG, LBG, and GG-were selected as soil stabilizers to enhance the strength characteristics of GRS. To evaluate the effectiveness of these biopolymers, unconfined compressive strength tests and direct shear tests were performed. Additionally, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were employed to examine changes in the soil's microscopic structure and to explore the underlying mechanisms responsible for the observed improvements in strength due to biopolymer treatment. Unconfined compressive strength tests and direct shear tests provide quantitative data on the soil's mechanical properties, evaluating the effect of biopolymers on soil strength and stability. SEM provides insights into the impact of biopolymers on the soil's microstructure, helping to understand the interaction between biopolymers and soil particles. XRD reveals the potential impact of biopolymers on the soil's mineral composition.