Macro-meso modified shear model of 3D-printed rock structural plane reinforced by basalt fiber low-carbon geopolymer mortar

The presence of a structural plane poses a serious threat to the safety of the surrounding rock in tunnels during construction. This study innovatively applied the optimized basalt fiber-reinforced geopolymer mortar (FR-GPM) to reinforce the 3D-printed rock structural plane, and proposed a modified shear strength model for grouted structural planes. The macro-shear response, mesoscopic characteristics, and failure mechanisms of the grouted structural plane were investigated using direct shear tests, acoustic emission (AE) techniques, and scanning electron microscopy. The results show that the compressive strength, shear strength, and tensile strength of the sample at 7 d and 28 d are 1.5 and 1.28 times, 1.31 and 1.28 times, and 1.48 and 1.37 times higher than those without fiber at a water-binder ratio of 0.5, an alkaline activator modulus of 1.2 with content of 8%, and a fiber content of 0.4% with a length of 4.5 mm. Moreover, the normal stress has the most pronounced effect on the shear response of the reinforced structural plane; the peak and residual shear stresses at 4 MPa are 1.55-2.25 times and 1.88-2.2 times higher than at 2 MPa. Furthermore, more cementitious material particles are stacked up at the interfacial transition zone of the 3D-printed complex structural plane, forming better-bonded structures. Additionally, the modified shear strength model can effectively estimate the peak shear strength of the grouted structural plane with a maximum error of only 4.08%. These research outcomes are expected to provide theoretical and technical support for the environmentally friendly and economic reinforcement of geological disasters caused by the structural plane.