Coral gravel soils, which are composite soils consisting of finger-coral fragments and silt matrix, are often found in coastal regions of sub-tropical islands, particularly in Okinawa. In this study, for reconstituted soils with various coral gravel fractions up to 44% that was the densest package, a series of triaxial CU-bar and CD tests was conducted to study determination method for soil design parameters in consideration of interaction between soil skeleton consisted of coral fragments and silt matrix. For samples with volumetric percentage of coral fragments less than 20%, the shear strength obtained from the CD tests was slightly larger than that obtained from the CU-bar tests; however, the difference between those two tests was very small. For samples with volumetric percentage larger than 20%, the shear strengths obtained from the CU-bar tests were significantly overestimated because of the unrealistically large negative excess pore pressure in the field corresponding to significant dilation. The shear strengths obtained from CD tests also show the similar tendency corresponding to the volume expansion; however, these are much smaller than those obtained from the CU-bar tests. For the samples with dense package of coral fragments, shear resistance angle ϕ was much larger than normal soils; however, it tended to decrease in association with particle crush of coral fragments. The tendency of particle crush was visually evidenced through CT-images observed before and after the triaxial tests. The soil parameters were significantly influenced by volumetric percentage of coral fragments in association with particle interaction and particle crush, when the percentage was larger than 20% for the coral gravel soils examined in this study.