Abstract: To analyze the interlayer sliding evolution patterns and deformation failure characteristics of layered composite rocks, we conducted a three-point bending test on a layered composite rock specimen composed of fine sandstone, using digital speckle correlation as the observation method. The main conclusions are as follows: (1) interlayer contact conditions (or occurrence of sliding) significantly influence the fracture sequence and peak load deformation characteristics of composite rocks. When sliding occurs at the interlayer contact surface, the upper rock layer is the first to undergo failure, and the peak load is smaller compared to the same structure without sliding. In this experiment, for instance, the peak load during sliding conditions was 56% of that without sliding. (2) During the deformation and failure process of layered composite rocks, the interlayer sliding displacement exhibits an overall fluctuating distribution. In the second set of experiments, the maximum sliding displacement reached 0.320 mm, whereas in the fourth set, it was only 0.027 mm, indicating a nearly 10-fold difference. Abrupt changes in sliding and vertical displacements were observed in different regions at the sudden drops of the load curve. However, the patterns of these abrupt changes differed between the second and fourth sets of experiments, primarily due to variations in the initial crack formation locations within the composite rock layers. (3) In our study, when sliding occurred at the interlayer contact surface of the composite rocks, the fluctuation amplitude of the ratio between horizontal and vertical stresses remained within 0.15. In contrast, when no sliding occurred, the fluctuation amplitude of the stress ratio was mostly confined to 0.5. (4) During the rupture of the upper rock layer accompanied by interlayer sliding, both horizontal and vertical accelerations were detected. Notably, the amplitude of vertical acceleration variations was approximately 50% of that of horizontal accelerations. Consequently, the energy released during the rock failure process propagates in both horizontal and vertical directions, specifically as shear waves and longitudinal waves. These research insights offer valuable implications for studying high-level rockbursts during coal mining operations and for understanding the deformation characteristics of overlying rock layers.

Key words: laminated composite rocks, three-point bending experiments, contact surface, interlayer sliding