Effect of joint density on mechanical behavior of rock mass: Insight from 3D printing tests and DEM simulation

The complex structure of rock masses makes their strength and failure behavior highly variable. The investigation of the strength and failure of jointed rock masses remains a critical issue in rock engineering. This study combined 3D printing experiments and numerical simulation to examine the effect of joint density on the mechanical properties of rock masses. A network of persistent joints was developed using 3D printing to create rock-like specimens that were then subjected to uniaxial compression tests. CT scanning was used to monitor the failure modes of the materials with different joint densities. Laboratory tests showed that the peak strength and elastic modulus of rock-like materials decayed as a power function with increasing joint density. Numerical simulations revealed the crack initiation, propagation, coalescence, and ultimate failure processes in specimens with varying joint densities under uniaxial compression. The results indicated that a higher normal stiffness of the joints led to a lower elastic modulus, whereas a greater shear stiffness resulted in a smaller elastic modulus. There is a threshold for joint cohesion. Below this threshold, the peak strength of the rock mass increases with increasing joint cohesion, and the strength increases linearly with the internal friction angle of the joints. Finally, the limitations of using 3D printing and numerical simulations to study the mechanical properties of natural rock masses were discussed.