![flac3d simulation of triaxial test flac3d simulation of triaxial test](http://docs.itascacg.com/flac3d700/_images/sleeve-initial-geom.png)
found that the effect of gradation on the stress-strain curve and volume strain-axial strain curve of coarse-grained materials is more significant under the condition of low confining pressure. believed that with the increase of the coarse-grained content, the permeability coefficient, and internal friction angle of the coarse-grained material tends to increase.
![flac3d simulation of triaxial test flac3d simulation of triaxial test](https://www.scientific.net/AMR.143-144.873/thumbnail.gif)
found that the increase of the coarse coarse-grained content will increase the strength of the coarse-grained material, and the degree of particle breakage will increase accordingly. Many scholars have studied the relationship between the gradation and the physical and mechanical properties of coarse-grained materials. The scale effect is mainly due to the fact that the scale changes the gradation composition of the coarse-grained materials, and the gradation is an essential factor affecting the physical and mechanical properties of the coarse-grained materials. Because the scale reduction changes the gradation of the original coarse-grained materials, the physical and mechanical properties of the coarse-grained materials are also significantly changed, which is the scale effect. The current method of studying this type of coarse-grained material is to reduce the gradation of the natural materials and try to estimate the actual strength parameters by measuring the strength parameters of the reduced coarse-grained materials. To determine the shear strength parameters of such coarse-grained materials, a giant instrument with a diameter of more than 5 meters and a height of more than 10 meters needed to be established, and its size is far beyond the size of existing instruments. Besides, the particle size of coarse-grained materials is very dispersed, and the size of large particles even exceeds 1 m. However, as a granular loose geotechnical material, the strength of coarse-grained materials is affected by gradation composition, particle shape, and intergranular force, mineral composition of rock, and other factors, so even coarse-grained material subjected to multiple same laboratory tests has the same gradation composition, and the results may not be consistent. Generally, the shear strength parameters of coarse-grained materials can be obtained through large-scale direct shear tests or large-scale triaxial tests. However, in practical engineering, the reasonable strength parameters of coarse-grained materials have always been a problem.
![flac3d simulation of triaxial test flac3d simulation of triaxial test](http://docs.itascacg.com/flac3d700/_images/modelssc-tri-undrained-pq.png)
Obtaining reasonable strength parameters of geomaterials is the primary task of studying the stability of such geotechnical engineering. Introductionīecause of good engineering properties, coarse-grained materials are widely used as the primary filling materials for railway ballasts, reservoirs, and dams and are also the main bulk geotechnical material piled up in the dumps of open-pit mines. The research results can provide a way of thinking for the study of the scale effect of coarse-grained materials and also have certain reference significance for inferring the strength parameters of the original-graded coarse-grained materials. If particle breakage and migration were assumed to be neglected, the internal friction angle φ and would be roughly proportional, the cohesive force c fluctuated with the increase of, and the empirical relations between and c and were established, respectively, which provides a reference for estimating the actual shear strength parameters of coarse-grained materials on-site. As the confining pressure increased, the scale effect of coarse-grained materials would be magnified. The results showed that under the same confining pressure, the peak stress and initial deformation modulus increased with the increase of the maximum particle size, while the degree of shear shrinkage and Poisson’s ration υ decreased. The failure process and the scale effect on the strength and deformation of coarse-grained materials were analyzed and discussed. The parallel grading method was adopted to create six grading curves for numerical simulation based on one in situ grading curve. By combining the self-developed cellular automaton program with laboratory experiments, a method of simulating the triaxial test of coarse-grained materials was proposed in this paper, and a triaxial test numerical specimen that can characterize the discontinuous, nonuniform, and heterogeneous characteristics of bulk geotechnical materials was established. The scale effect is an unavoidable problem in the laboratory test of coarse-grained materials.