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 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.