Experimental and numerical study on cross-layer mechanical characteristics and failure mechanism induced by grouting in interbedded rocks

Abstract Deep geotechnical engineering requires grouting technology to ensure project safety. However, the interlayered geological conditions of layered rock formations make grouting effectiveness difficult to predict and guarantee. Therefore, it is of significant practical value to investigate the diffusion mechanism of grouting within layered rock masses further. First, this study developed a true triaxial grouting physical testing system to reveal the influence of water-to-cement ratio (W/C) and injection rate on grout diffusion. The evolution of acoustic emission characteristics under different grouting parameters was compared and analyzed. Furthermore, potential fracture mechanisms within layered rocks were identified through moment tensor inversion. The results indicate that cement slurry spreads more readily within weak layers at low injection rates and W/Cs, facilitating generation of multiple small-scale fractures. Peak fracturing pressure exhibits a positive correlation with the injection rate and a negative correlation with W/C. Acoustic emission localization results indicate that higher injection rates facilitate slurry diffusion perpendicular to weak layers. Furthermore, a hydraulic-mechanical-damage coupled model for simulating grouting in layered rocks was developed using COMSOL Multiphysics software. By numerical simulation, the regulatory mechanisms of weak layer dip angle and in-situ stress on dominant diffusion directions were revealed. Compared results revealed that when longitudinal stress was the maximum principal stress, a steeper weak-strength layer inclination tended to confine slurry within high-strength layers. However, the initial cracking pressure first decreased then increased with weak layer inclination, approaching its minimum at 45°. This work systematically investigates the fracture mechanism induced by grouting in layered rocks by integrating laboratory physical tests with numerical simulations that account for weak layer dips and in-situ stress fields. The relevant findings and insights provide valuable practical references for underground geotechnical engineering.