Research on shear strength models for unsaturated soils considering fine particle contents

The shear strength of unsaturated soils is influenced not only by saturation and matrix suction, but also significantly by the content of fine particles. At present, no shear strength model has been established that accounts for the effect of fine particle content. To elucidate the influence of fine-grained content on the shear strength of unsaturated soils, analysis of cohesion variation mechanisms reveals that increased fine-grained content alters particle contact relationships and spacing. This affects the water-bend liquid surface, causing matrix suction to initially increase before decreasing, resulting in a peaked variation pattern for cohesion. Secondly, based on the dual-stress variable theory and its superiority over other models, combined with the capillary action mechanism at curved liquid surfaces, a shear strength prediction model accounting for fine-grained content was established by introducing constitutive variables and the contribution strength of fine particles. Through comparative validation, this model has been shown to accurately predict the shear strength of soils with varying fine particle contents. The physical significance of each parameter within the model has been clarified, and approximate ranges for these parameters have been provided. This model is suitable for predicting the strength characteristics of unsaturated soils with smaller particle sizes.