Study on regression model of shear strength of root-soil composite under freeze-thaw action

Currently, the deterioration mechanism of root containing soil performance under freeze-thaw cycles remains poorly understood, and existing prediction models seldom systematically account for the influence of freeze-thaw cycles. In this study, the reed root-sandy silt in the Inner Mongolia section of the Yellow River was taken as the research object. The effects of initial water content w, initial dry density ρ_d, confining pressure σ, root section ratio RAR and freeze-thaw cycles n on the shear strength τ, cohesion c and internal friction angle φ of reed root-sandy silt were investigated. The sensitivity of each factor was analyzed. Based on the above parameters, the regression model of reed root-sandy silt τ, c and φ in the Inner Mongolia section of the Yellow River was constructed. The results show that τ, c and φ are positively correlated with ρ_d and negatively correlated with w, and τ is positively correlated with σ. τ and c are greatly affected by n and decay exponentially, while φ is less affected by n and increases slightly linearly. There is a quadratic function relationship between soil τ, φ and RAR, and a Gaussian function relationship between c and RAR. The influencing factors for τ rank in the order: σ > ρ_d and RAR > n > w, c is: n > ρ_d and RAR > w, φ is: ρ_d and RAR > n > w. The interaction between w and n is not significant for τ, c and φ of bare soil and root-soil composite, while the interaction between w and ρ_d, n and ρ_d, w and RAR, n and RAR is significant for τ, c and φ of bare soil and root-soil composite. Based on the interactions among factors such as w, ρ_d, σ, RAR and n,the general regression model for τ, c, φ, the Coulomb regression model of shear strength, and the Wu regression model for shear strength all perform well. They can be used to estimate the strength of reed root-silty sand in the Inner Mongolia section of the Yellow River, providing technical guidance for riverbank protection engineering.