Study on time effect and prediction model of shear strength of root-soil complex under dry-wet cycle

Triaxial compression tests were conducted on the alfalfa root-loess complex at different growth stages obtained through artificial planting. The research focused on analyzing the time variation law of shear strength index and deformation index of the alfalfa root-loess complex under dry-wet cycles. Additionally, the time effect of shear strength index of the alfalfa root-loess complex under dry-wet cycles were analyzed and its prediction model put forward. The results show that the PG-DWC (dry-wet cycle caused by planting management and watering during plant growth period) causes the peak strength of plain soil to change in a "V" shape with the increase of growth period, and the peak strength of alfalfa root-loess complex is higher than that of plain soil at the same growth period. The deterioration of the peak strength of alfalfa root-loess complex in the same growth period is aggravated with the increase of drying and wetting cycles. Compared with the 0-day growth period, the effective cohesion of alfalfa root-loess complex increased the most at 180 days, which were 33.88%, 46.05%, 30.12% and 216.02% respectively. When the number of dry-wet cycles is constant, the effective cohesion of the alfalfa root-loess complex increases with the growth period. However, it gradually decreases compared to the long-term growth trend of the previous life, with the smallest increase observed at 180 days. For the same growth period, the effective cohesion of the alfalfa root-loess complex decreases with an increase in drying and wetting cycles. This indicates that EC dry-wet cycle (the dry-wet cycles caused by extreme natural conditions such as continuous rain) have a detrimental effect on the time effect of the shear strength of alfalfa root-loess complex. Finally, a prediction model for the shear strength of the alfalfa root-loess complex under dry-wet cycles was proposed, which exhibits high prediction accuracy. The research results provide useful guidance for the understanding of mechanical behavior and structural damage evolution of root-soil composite.