## 3 Test Results and Analysis  
### Unconfined Compressive Strength  
Figure 2 illustrates the unconfined compressive strength (\(q_{u}\)) and stress-strain (\(\epsilon_{1}\)) curves for crushed gravel soil that has been stabilized with varying amounts of xanthan gum and lignin. The figure illustrates that the curves for both the crushed gravel soil and the soil stabilized with varying dosages of xanthan gum and lignin initially increase before subsequently decreasing. In light of the observed trend in these curves, the response can be classified into four distinct stages. 1 Compaction Stage: At low stress levels, the voids between soil particles and sandstone particles undergo compaction, resulting in a nonlinear increase in the stress-strain curve. 2 Linear Elastic Stage: As the axial load continues to increase, no internal damage occurs at this stage, and the deformation remains reversible, with the curve showing a linear increase. 3 Crack Propagation Stage: When the load reaches the crack initiation strength of the specimen, microcracks begin to form on the surface and progressively develop into prominent macroracks. The curve shows a rapid upward trend during this phase. 4 Post-Peak Stage: Under continuous axial loading, the deformation of the specimen rapidly increases. After the peak strength of the specimen is reached, the load capacity sharply decreases, and the stress-strain curve shows a steep drop. This is because with the incorporation of xanthan gum and lignin, the two in contact with water will form a cement to fill the gaps between the geotechnical particles, thereby increasing the cohesion and friction angle between the specimen micro-particles, and thus increasing the specimen's load-bearing capacity, so that the crushed rock soil cured by xanthan gum and lignin has a higher peak strength than the natural soil. And as the axial strain continues to increase, the surface of the specimen will form an inclined shear fracture surface. In view of the role of internal cohesion and friction angle of the specimen, the specimen is able to maintain a certain amount of residual strength, and xanthan gum and lignin can effectively increase the specimen's cohesion and friction angle so that compared with the natural soil, the residual strength of the treated specimen is higher [33; 34; 35].  
The unconfined compressive strength of gravel soil stabilized with different amounts of xanthan gum and lignin is shown in Figure 3. The unconfined compressive strength of gravel soil stabilized with xanthan gum and lignin is higher than that of natural soil. As the xanthan gum content increases, the unconfined compressive strength of the sample shows a linear upward trend with an increase of 97.31%. This is attrib  
Figure 2: Axial stress–axial strain curves for unconfined compressive tests.  
filling the voids between the soil and rock particles, thereby increasing the load-bearing capacity of the sample. The unconfined compressive strength of lignin shows the law of first increase and then decrease; at a dosage of 4%, the unconfined compressive strength is the largest, increased by 60.05%; as the dosage continues to increase, the unconfined compressive strength begins to decay. This is mainly because the lignin solidification bonded in the soil particles on the surface and in the pore space to increase the strength of the specimen, and the lignin dosing reached 6%; its content is relatively too much, resulting in the compression of the specimen appearing in the local softening phenomenon [36]. These research results can provide a reference basis for the optimal dosage of xanthan gum and lignin to improve gravel soil in actual projects, which can help to save natural resources and reduce the engineering loss, and then provide a strong feasible support for the research of mixing technology.