Reinforcement Effect of T. repens L. Influenced by Soil Depth, Plant Density and Growth stage: Experimental Analysis and Root Cohesion Models

• Provide a detailed analysis of how soil depth, plant density, and growth stage influence the morphological and mechanical characteristics of T. repens L. roots, in preparation for analyzing their reinforcement effect on soil. • Analyze the reasons behind the decrease in root cohesion. • Propose an empirical correction model for root cohesion by taking into account the tensile strength and flexural strength of roots. • Demonstrate the applicability of the empirical correction model across different plant densities and growth stages. Trifolium repens L. ( T. repens L.), a globally distributed legume, is commonly cultivated along streambanks owing to its broad environmental adaptability. However, the reinforcement mechanism of T. repens L. roots remains insufficiently characterized. This study comprehensively investigated the morphological characteristics of T. repens L. roots concerning soil depth, plant density, and growth stage. The tensile strengths of roots broken simultaneously and progressively ( t r and s r ), along with flexural strength ( f r ) were examined. The variation patterns in the shear strength of the T. repens L. root-reinforced soil were also analyzed. Results indicated a decrease in cohesion at the 12-month growth stage, which may be attributed to the changes in soil structure and specimen size in the shear test. Root cohesion ( c r ) was calculated using classical models, but the models proved inadequate for capturing the complexity. According to existing research, linear functions were employed to model the relationships between c r and t r , c r and s r , as well as c r and f r , respectively. Among these, c r exhibited a stronger correlation with s r . However, these functions remained insufficient for accurate calculations. Considering root bending, an empirical correction model relating c r to s r and f r was proposed and validated, achieving error rates below 15%. This model can calculate c r for T. repens L. root-reinforced soil regardless of variations in plant density and growth stage, but further improvements are still necessary.