INFLUENCE OF PLANT SPECIES AND ROOT GROWTH PERIOD ON THE MECHANICAL BEHAVIOR OF LOESS SOIL IN DRAINED TRIAXIAL TESTS

Vegetation is increasingly used for shallow loess-slope stabilization, yet its growth-dependent reinforcement mechanisms remain insufficiently quantified. This study investigates the growth-dependent mechanical behavior of root-reinforced loess using consolidated-drained triaxial tests. Loess specimens were cultivated for 30, 60, and 90 days with plant species exhibiting contrasting root architectures (fibrous-rooted Festuca arundinacea and Lolium perenne, and tap-rooted Medicago sativa L.) and tested under confining pressures of 50, 75, and 100 kPa. Results show that reinforcement depends on both plant species and growth period, as root biomass accumulation significantly enhances peak strength and stiffness while reducing volumetric contraction. Peak deviatoric stress increased by 30-60% from 30 to 90 days, with increases consistent with root biomass development. Among the species, M. sativa L. produced the highest strength gains and largest reduction in volumetric contraction, followed by L. perenne and F. arundinacea. Failure-envelope analysis showed that reinforcement was governed primarily by species- and growth-dependent increases in apparent cohesion. These findings provide a basis for incorporating vegetation growth periods and species selection into the engineering assessments of loess slopes, and for guiding the development of constitutive models