Size effect and anisotropy of mechanical properties of fractured rock masses based on 3D printing

The size effect and anisotropy of the mechanical parameters of fractured rocks are difficult tasks that need to be solved in the field of rock mechanics and engineering. Making full use of the advantages of rapid prototyping and batch preparation of complex internal structure rock models with 3D sand printing technology, the rock-like specimens with different sizes and different rotation angles of the fracture network model are produced by using 3D sand printing, the quartz sand and furan resin are employed as the printing materials. The uniaxial compression test is performed on the 3D sand printed specimens to study the size effect of the mechanical properties of the fracture network rock mass, the correlation between fracture density and strength is revealed and the anisotropy of the mechanical properties of rock masses at the representative elementary volume (REV) scale is analyzed. The test results show that the mechanical properties of 3D sand-printed specimens are similar to those of natural rocks, the stress-strain curves of the fractured network model-like rocks can be divided into four stages: original crack closure stage, linear elastic deformation stage, crack initiation and extension stage, and post-peak stage. There is an exponential decay relationship between uniaxial compressive strength and size of the specimens, and there is an obvious characteristic of size effect. There is a significant negative exponential relationship between fracture density and compressive strength, and the size of the REV determined based on the fracture density and compressive strength is well consistent. The failure patterns and compressive strength of the fractured rocks have obvious anisotropic characteristics. The research approach provides a reliable method for the laboratory experiments to study the size effect and anisotropy of complex fractured rock masses.