Effect of Particle Shape on Dilative Behavior and Stress Path Characteristics of Chamkhaleh Sand in Undrained Triaxial Tests

Abstract

The behavior of Chamkhaleh sand and three other recognized sands namely, Babolsar, Firouzkuh, and Standard (Ottawa) sands are compared using triaxial apparatus under undrained monotonic loading conditions. Chamkhaleh and Babolsar sands are supplied naturally from southern Caspian Sea shorelines, whereas artificial Firouzkuh and Standard sands were supplied commercially. Samples were prepared using wet tamping with regard to the reduced compaction effect at relative density of 15 % under isotropic consolidation pressures of 100, 300, and 500 kPa. The results of triaxial tests have indicated that Chamkhaleh sand has much more dilation tendency than the other sands. To evaluate the reasons behind this behavior, the sphericity and roundness of all the four sand particles were measured using an image processing method. It was revealed that the sphericity of the four sands is not much different, but Chamkhaleh sand is more angular than the other sands. For comparison of the dilative response of the sands in undrained triaxial tests, a “dilation tendency index” is introduced. This index may be used as a criterion for measuring the dilation of sands in undrained tests. Results have shown that the internal friction angle under the steady-state condition is more dependent on the shape of particles than the maximum strength condition. For sphericities greater than 0.5, the dependency rate of sand behavior on the roundness is decreased.