# Experimental Study on Scour Resistance Performance Enhancement of Chongqing Red Clay
## 3 Results and Discussion
### Scour Resistance Analysis  
Critical shear stress refers to the hydrodynamic shear stress corresponding to the critical state at which soil transitions from static to motion under water flow. The experimental results of critical shear stress for solidified soil are shown in Figures 13-15, with photographs of the scouring initiation process provided in Figure 16. The results demonstrate that critical shear stress exhibits significant influences from cement content, water-to-solid ratio, and curing duration but minimal impact from curing agent dosage. As shown in Figure 13, the critical shear stress increases with prolonged curing time but exhibits no clear correlation with curing agent dosage. Previous experimental results revealed that while increased curing agent dosage enhances cohesion between red clay particles, it does not proportionally improve scour resistance. This phenomenon may be attributed to the dual effects of the curing agent: although it strengthens interparticle cohesion, it simultaneously forms a membranous coating around cement particles, hindering their contact and hydration reactions with water. While enhancing cohesion, the curing agent also inhibits cement strength development, leading to non-monotonic trends in scour resistance with increased dosage. Increasing curing agent dosage fails to improve scour resistance, raises material costs, and reduces flowability. Therefore, the optimal curing agent dosage should only meet anti-dispersion specifications (\(\geq\)0.3%) without additional increments for scour protection. Figure 12: Relationship model between flowability and suspended solids content. Figure 13: The effect of curing agent content on the critical shear stress of solidified soil. Figure 16: Experimental photographs of the scouring initiation process for solidified soil. (**a–d**) represent the stages of progressively increasing flow velocity, and (**e**) corresponds to the attainment of critical shear stress. Figure 14: The effect of cement content on the critical shear stress of solidified soil. Figure 15: The effect of water-to-solid ratio changes on the critical shear stress of solidified soil. The influence of cement content on critical shear stress is shown in Figure 14. As curing time increases, the critical shear stress of solidified soil gradually rises. At 1-h curing, solidified soils with different cement contents exhibit minimal differences in critical shear stress, but these differences become increasingly pronounced with prolonged curing, demonstrating higher critical shear stress at greater cement contents. This indicates that cement's solidification effect on red clay develops progressively during curing and intensifies over time. This phenomenon may arise because cement hydration proceeds gradually: minimal early-stage hydration contributes little to scour resistance, while prolonged curing enables cement to participate in hydration reactions, producing calcium silicate hydrate (C-S-H), ettrinigite (AFt), and other products that form a three-dimensional network structure. This network fills pores between red clay particles, enhances interparticle cementation strength, and improves the overall performance of red clay. Additionally, although red clay inherently possesses strong cohesion, its strength drastically diminishes upon water absorption. Enhancing its scour resistance relies on boosting interparticle cohesion and reducing water adsorption. Cement hydration consumes free water between particles, thereby lowering water adsorption, while hydration products cement particles to strengthen cohesion. Increased curing duration and cement content amplify free water consumption and interparticle cohesion. Consequently, higher cement contents accelerate the growth of scour resistance with curing time, yielding superior scour resistance at equivalent curing durations.