# Experimental Study on Scour Resistance Performance Enhancement of Chongqing Red Clay
###### Abstract  
To effectively utilize Chongqing's solid waste red clay for scour protection of local cross-river bridge foundations, this study modified Chongqing red clay using curing agent and cement, focusing on the effects of curing agent dosage, cement content, and water-to-solid ratio on the flowability, anti-dispersion performance, and scour resistance of solidified soil. Microstructural characteristics were observed via SEM, with formula fitting performed for two key parameters. Results indicate that an increased curing agent dosage significantly reduces flowability and suspended solids content of solidified soil while negligibly affecting critical shear stress; elevated cement content markedly enhances critical shear stress, slightly improves short-term flowability with reverse effects over time, and minimally impacts anti-dispersion performance; reduced water-to-solid ratio mitigates free water-induced cohesion weakening, lowering suspended solids content and flowability while increasing critical shear stress. Microstructural analysis reveals that generated C-S-H gels and ettringite (AFt) effectively fill pores, enhance matrix integrity, and improve scour resistance. A suspended solids content-flowability relationship model (R\({}^{2}\) = 0.977) established through quadratic polynomial regression demonstrates excellent predictive performance. The optimal mix proportion (0.3% curing agent, 10% cement, 0.5 water-to-solid ratio) meets specifications and construction requirements, serving as the optimal solidified soil formulation for scour protection. red clay; dispersion resistance; fluidity; scour resistance; critical shear stress; microstructure 2020 IEEE/RSJ International Conference on Acoustics and Electronics (ACoustics and Electronics)  
rings [11; 12], scour prevention trenches [13], and sacrificial piles [14]. However, these methods generally suffer from defects such as coupling failure at contact interfaces, poor adaptability to multidirectional flow fields, and high maintenance costs [15; 16; 17; 18]. Passive protection methods focus on enhancing the anti-scour capacity of riverbeds, mainly through techniques like enlarged foundations [19], concrete protection, partially grouted riprap, and riprap placement [20]. Nevertheless, they encounter challenges, including difficulties in positioning during deep-water construction, shrinkage strain in mass concrete, accumulation of hydration heat, and sudden stiffness changes at contact interfaces [21; 22]. Fundamentally, traditional protection methods predominantly rely on macroscopic engineering experience while neglecting the microscopic mechanisms governing soil-water-material multiphase interface interactions. The application of pre-mixed flowable solidified soil for scour protection of bridge foundations represents an emerging technology in recent years, utilizing soil, cementitious materials, water, and curing agents as raw materials to overcome the limitations of traditional protective measures through microscopic synergistic mechanisms. Its core advantages include (1) elastic modulus of solidified soil matching the riverbed matrix to avoid interface modulus discontinuity; (2) elimination of hydration heat-induced cracking risks associated with mass concrete; (3) local material utilization, environmental friendliness, and low cost [23]; (4) suppression of particle loss by enhancing the soil's inherent shear strength. Regarding the use of solidified soil for scour protection of bridge abutment foundations, a number of scholars have conducted studies. [PERSON] et al. [24] investigated the scour resistance of four single-sized soil samples (d = 0.075 mm, 0.25 mm, 0.5 mm, and 2.0 mm) and four mixed soil samples under varying hydrodynamic conditions. Their study revealed that particle composition significantly influences scour resistance, with well-graded soils exhibiting far superior performance compared to poorly graded soils, while compaction degree had less impact than particle size. [PERSON] et al.