Three-dimensional numerical simulation of soil stabilization effects by different root morphologies and analysis of bank stability

Extensive wind-deposited sandy soils line the middle and lower reaches of the Tarim River, rendering its banks vulnerable to erosion. Under fluctuating rainfall and water levels, these banks are highly susceptible to collapse and failure. Natural vegetation serves as an effective soil stabilization measure, significantly enhancing slope stability. To investigate the soil-stabilizing effects of different root morphologies, pull-out and shear tests were conducted on the root systems of four plant species: Haloxylon ammodendron, Alhagi camelorum, Tamarix tarimensis, and Phragmites australis. Finite element modeling was employed for three-dimensional analysis, simplifying the root systems into four distinct three-dimensional models: Shuttlecock-shaped, heart-shaped, tap-shaped, and plate-shaped. This study investigates the patterns of slope stability variation under the reinforcement effects of these diverse root morphologies. Results indicate: (1) Root tensile strength is inversely proportional to root diameter, with larger roots exhibiting lower tensile strength. Root volume density (RVD) first increases and then decreases in its effect on the shear strength of root-soil composites. Among the four root-soil composites, the enhancement of cohesion follows the order: Tamarix tarimensis > Phragmites australis > Alhagi camelorum > Haloxylon ammodendron. (2) Under rainfall conditions, among the four root morphologies, the tap-shaped root system demonstrated the most significant enhancement to slope stability, with the safety factor increasing by up to 13.04%. When rainfall intensity reached 240 mm/d, the maximum displacement of the bare slope was 0.05557 m, while that of the tap-shaped root system was 0.02615 m. The displacement contour surfaces differed between bare slopes and vegetated slopes. The displacement contour surface of the bare slope extended across the entire slope face to the crest, exhibiting a crescent-shaped pattern. The displacement contour surfaces of vegetated slopes are relatively smaller and predominantly concentrated near the toe. The safety factor of the slope increases with root depth; at a root depth of 1.75 m, the safety factor improves by 41.16%. (3) Under conditions of rapid water level drop, the tap-shaped root system exhibited the greatest increase in the safety factor for the slope, reaching 14.58%. When the water level change rate was 2.0 m/d, the maximum displacement of the bare slope was 0.08967 m, while the plate-shaped root system among the four root morphologies produced the smallest displacement at 0.05751 m. Among these, the displacement contour surfaces for the heart-shaped root system slope extended across the entire crest at water level change rates of 1.0 m/d and 2.0 m/d, exhibiting the largest displacement among the four root systems.