Mechanical properties and failure mechanisms of anisotropic rough jointed rocks reinforced by carbon nanotube grouting material

Jointed rock masses, widely distributed in geotechnical engineering, often exhibit anisotropy and discontinuity that severely compromise the stability of underground structures, yet conventional cement-based grouting materials provide limited reinforcement due to inherent micropores and weak interfacial bonding. This study systematically investigates the enhancement effects of carbon nanotube (CNT) modified grouting material on the mechanical properties and deformability of rough jointed rock masses. Firstly, an optimized process involving polyacrylate superplasticizer (PCA) and humic acid (HA) assisted ultrasonic dispersion was employed to achieve uniform dispersion of CNTs, followed by the casting of grout-reinforced rough jointed rock samples with varying joint surface dip angles ( α = 0° ∼ 90°). Uniaxial compression tests were conducted, combining acoustic emission (AE) and digital image correlation (DIC) monitoring techniques, to quantitatively compare the reinforcement effects of CNT grouting material with ordinary cement grouting material. The discrete element method-based particle flow numerical simulation (PFC) was utilized to analyze the number and distribution of tensile and shear cracks, as well as the anisotropy of displacement field. The results indicate that, compared to ordinary cement grouting material, the CNT grouting material significantly enhanced the mechanical performance of jointed samples due to the micro-pore filling and bridging effects of CNTs. The peak stress increased by up to 99.5% (at α = 60°), and the elastic modulus was significantly improved. The increased shear stress on the joint surface promoted shear slip, causing the peak stress to initially decrease and then increase with increasing α , reaching its minimum value at α = 60° or 75°. Jointed rock samples modified with CNT grouting material exhibited more active AE responses and higher cumulative counts during the yielding stage, attributed to CNT-induced toughening, microstructural optimization, and interface strengthening. As α increased, the failure mechanisms of the jointed samples transitioned from tensile-dominated to shear-dominated failure modes due to the increased shear stress on the joint surface. These findings demonstrate that CNT-modified grouting materials can substantially enhance the mechanical performance and stability of rough jointed rock masses. The results provide theoretical guidance and technical support for the design of high-performance grouting reinforcement in underground engineering projects such as tunnels, slopes, and deep roadways.