The true three-dimensional stress state of coral sand in actual engineering can be realized by using true triaxial test

but the influence of coefficient of intermediate principal stress b on the mechanics of coral sand in the existing true triaxial test is not considered deep enough. In this paper

true triaxial experiments of coral sand with different average principal stresses p and the coefficients of intermediate principle stress b were carried out to study the effects of coefficient of intermediate principal stress and average principal stress on particle breakage

strength and deformation of coral sand particles. The results show that the increase of b will reduce the shear stress

shear strain and volumetric strain of coral sand

while the increase of p will have the opposite effect on the stress-strain curve of coral sand. The critical state theory is applicable to coral sand in the true triaxial state. The effects of b and p on the particle breakage

the deviator stress in critical state and the friction angle of coral sand are different. According to the relationship between particle breakage

strength and deformation

the empirical formula of strength considering the influence of particle breakage was fitted

and the dilatation equation of coral sand considering particle breakage under true triaxial conditions was derived. The research results can provide theoretical support for the construction of coastal engineering in coral sand foundations.