Influence of drainage and root biomass on soil mechanical behavior in triaxial tests

This paper presents a study in which triaxial tests were performed on loess soil reinforced with natural roots. Triaxial compression tests were performed on soil specimens with root biomass of 0.25, 0.5, 1.0, and 1.25% and subsequently consolidated at various confining stresses under drained and undrained conditions. The results are presented in terms of monotonic stress–strain behavior, volumetric behavior, failure envelope, and shear strength parameters. The test results showed that the inclusion of roots required higher confining stress to prevent failure. The reinforced specimen showed continued mobilization of dilatancy in drained and undrained conditions and resulted in exhibiting higher peak deviator stress compared to the unreinforced specimen. The specimen with the lowest root biomass exhibited the least increments in the hardening response, while the specimen with the largest root biomass showed the highest hardening response. The addition of roots decreased the contractancy of soil in both drained and undrained condition. Under the same root content and confining pressure, the shear strength in an undrained condition is much higher as compared to drained conditions. The largest improvement in soil's mechanical behavior was observed at smaller confining pressure, i.e., 100 kPa in both drained and undrained conditions. The addition of roots also increases the initial yielding of the soil, which is the function of roots biomass. The output of this research will provide a foundation for the future development of the predictive constitutive model for soil–root composite and its applications to slope stability.