Shear strength-dilation characteristics of coral sand contained fines

Coral sand (CS) always contain different contents of fines and consequently cause some changes to shear behavior which is distinct from the regular silicious sand. To examine the effects of stress level (σ₃), fines (FS), and relative density (D_r) on shear strength-dilation behaviors of CS, a series of consolidated drained tests and gray correlation analysis were conducted. Results show that peak strength of sandy soil improved by increasing σ₃ and D_r but reduced as increasing FS content. However, the peak strength loss rate η increased with an increase of D_r or FS content but decreased as increasing σ₃. In addition, strain softening of mixture was aggravated by increasing σ₃, D_r, and FS percentage. Particularly, the shear dilatancy of mixture transformed to shear contraction as σ₃ increased from 200 to 400 kPa. Maximum angle of dilation has an approximate linear relation with peak-state friction angle. Gray correlation analysis indicated that the influence of stress level and FS content on peak strength and strain-softening of sandy soil is more prominent than D_r. Furthermore, when D_r increased or FS content decreased, the internal friction angle of mixture increased linearly. The cohesion force of mixture has a positive linear relation with D_r while appears a hyperbolic relation with FS content. Based on the concept of equivalent void ratio, the grain contact and mixture phase were discussed. Finally, the modified Mohr-Coulomb criterion of mixture was proposed considering D_r and FS content.