A Comparative Study on Shear Behavior of Uniform-, Gap-, and Fractal-Graded Carbonate Soils

This paper presents a comparative study on shear responses at the phase transformation, peak, and critical states together with the evolution of particle breakage of uniform-, gap- and fractal-graded carbonate soils. A total of 90 sets of drained and undrained triaxial tests were conducted at relative densities of 30%, 60%, and 90%, under a wide range of confining pressures. The test results show that the phase transformation friction angles ${\phi }_{pt}^{\prime }$ during drained and undrained shearing are approximately the same, and share the same trend with increasing relative density and confining pressure. The stability of the sample for the undrained test (quantified by the ratio of mean effective stress at phase transformation state $p_{pt}^{\prime }$ and initial confining pressure ${\sigma }_c$), peak friction angle ${\phi }_p^{\prime }$, and peak dilatancy angle ${\psi }_p$ for the drained test decrease with increasing confining pressure with the reduction rate decreasing sequentially for the uniform-, gap- and fractal-graded samples. The intercept and slope of the critical state lines (CSLs) of the carbonate soils vary with the initial particle size distribution (PSD) in the $e\text{-}\log p^{\prime }$ space, while the CSLs in the $p^{\prime }\text{-}q$ space appear to be unique regardless of the initial PSD. The crushing capacity, characterizing the crushing potential of a soil sample, was proposed and quantified by a newly proposed parameter $a$. It is also found that the value of parameter $a$ is well correlated with the parameters corresponding to the stability, strength, and deformation responses of carbonate samples.