Large-scale true triaxial experimental study on the stress path dependence of mechanical properties of coarse-grained material

The mechanical characteristics of coarse-grained materials exhibits a significant dependency on the stress path, and the large-scale true triaxial tests of complex three-dimensional stress paths are rarely reported. To investigate the influence of stress paths on the deformation and strength characteristics of coarse-grained materials, large-scale true triaxial isotropic consolidation and drained shear tests were carried out under two stress paths: constant minor principal stress σ3 and intermediate principal stress coefficient b (constant σ3 and b), and constant mean normal stress p and intermediate principal stress coefficient b (constant p and b). The results indicate that the stress path has a significant influence on the stress-strain relationship. As the intermediate principal stress coefficient b increases, the stress-strain curve under the stress path of constant σ3 and b gradually ascends and becomes steeper, and the volumetric contraction deformation gradually enlarges. However, under the stress path of constant p and b, the stress-strain curve descends and becomes more gradual, and the volumetric change initially compresses and then expands, accompanied by an increase in the volumetric change rate, and the dilatancy deformation gradually increases. The intermediate principal strain undergoes a transition from dilation to compression as the intermediate principal stress coefficient, b increases from 0 to 0.25. When b exceeds 0.25 and reaches 1.00, the intermediate principal strain consistently exhibits compressive behavior, and the compressive deformation gradually increases. The stress path exerts a pronounced influence on the strength of coarse-grained material. Under the constant σ3 and b stress path, the strength progressively enhances with the increasing intermediate principal stress coefficient, b. Conversely, a progressive diminution of strength is observed under the constant p and b stress path as b increases. The peak internal friction angle exhibits a positive correlation with the intermediate principal stress coefficient b, and the peak internal friction angle of the constant p and b stress path is higher than that of the constant σ3 and b stress path. Additionally, lower consolidation stresses yield greater peak internal friction angles. The failure stress ratio exhibits a monotonic decrease with diminishing decrement rates as the intermediate principal stress coefficient b increases from 0 to 0.75, while lower consolidation stresses correspond to higher failure stress ratio. When the intermediate principal stress coefficient varies between 0.75 and 1.00, the failure stress ratio basically remains constant. The stress path exerts a significant influence on the deformation and strength characteristics of coarse-grained materials under three-dimensional stress states. Accurate understanding of these mechanical characteristics is crucial for scientific implementation of earth-rockfill dam engineering.