Strength test of 3D printed artificial rock mass with pre-existing fracture

Discontinuities or structural planes are widely distributed in natural rock masses and significantly influence their geo-mechanical and geometric properties. Herein, a batch of rock samples, each with a single structural plane, is created using a 3D printer equipped with two robotic manipulators. One of the manipulators is connected via a nozzle to a concrete pumping truck, which can extrude brittle rock-like material to form layered intact rock masses; the rock-like material is mainly composed of cement, silica fume, sand and water. The other manipulator features a knife, which can carve discontinuities onto each layer of the printed model. By means of this system, rock masses with discontinuous joints are formed, and the failure strengths of rock masses with different joints are demonstrated via uniaxial compression tests and direct shear tests. The results thereof obtained via digital image correlation technology show that discontinuities lower the strength of the rock mass models significantly. With the increase of the angle between the fracture and horizontal plane, the uniaxial compressive strength first decreases, and then increases. During shear testing, the shear strength of the rock mass models increases with the surface roughness of the preset joint. These test results indicate that the influence of artificial joints on the mechanical properties of the models is consistent with that of natural rock mass joints. Using digital modeling and 3D printing technology, cracks hidden in a rock mass can be reproduced.