Abstract: A series of drainage triaxial shear tests under different stress paths is carried out on calcareous sand in the South China Sea. The particle breakage and shear strength characteristics of calcareous sand under complex paths are systematically studied. The research shows that the mechanical properties of calcareous sand change regularly with the deflection of the shear loading direction. When the stress path is in the loading zone, with the clockwise deflection of shear path, the softening degree and shear strength increase; the dilatability, the peak internal friction angles decrease, and particle breakage increases. When the stress path is in the unloading zone, the calcareous sand breaks suddenly, and the particle breakage is relatively large. There is a "0 initial average effective stress" stress path boundary, and the effect of initial average effective stress on the volume change on both sides is completely opposite. Based on fractal theory, an empirical formula for predicting B_r value under different consolidations, shear paths and initial average effective stress is established, and the complex influence mechanism of stress path and particle fracture coupling on the shear behavior of calcareous sand is revealed. According to the test results, the generalized additive models (GAMs) are used to derive the strength envelope considering the effects of particle breakage and stress paths, which can be used as the basis for predicting the peak strength of calcareous sand under different stress paths.

Key words: stress path, calcareous sand, particle breakage, fractal theory, generalized additive models