Abstract: In order to study the influence of joint density on the strength characteristics and failure modes of rock mass, the rock-like specimens with different joint densities were prepared by using 3D sand printing, with the quartz sand and furan resin being employed as the printing materials. The uniaxial compression test was performed on the 3D sand printed specimens, and the digital image correlation (DIC) method was used as a non-contact technique to monitor the full-field deformation. The crack initiation, propagation and coalescence behaviors were quantitatively analyzed from the micromechanics point of view. The results show that the shape of stress-strain curve and the compressive-to-tensile strength ratio of 3D sand printed intact specimen are similar with those of the natural rock, which can be grouped as a rock-like material. The variation processes of stress-strain curves with different joint densities are similar, and can be divided into initial compaction, linear elastic deformation, crack development and residual strength stages. The mechanical properties of specimens decrease with the increase of joint density εf, and the relationship can be expressed as exponential decay functions. By calculating the strain field and displacement vector distribution on the specimen surface, the deformation field distribution and crack propagation of the specimen are found to be closely related to the joint density. The failure mode shifts from axial tension failure (εf = 0.280%) toward mixed failure (εf = 1.193%) and then to tensile coalescence band failure (εf ≥ 1.712%) as the flaw density increases. When the joint density is greater than or equal to 2.739%, the block rotation appears in the tensile coalescence band, and the bookshelf faulting with block rotation is reproduced.

Key words: rock mechanics, joint density, 3D printing, failure mode, digital image correlation (DIC) method, displacement field