## 4 Analysis of Damage Characteristics
### Destruction Mode  
From the damage process, it can be seen that different bedding angles lead to different crack propagation trajectories. By compiling the shear stress damage clouds of the residual stages of the four bedding strength specimens under different bedding angles and focusing on the process of crack propagation (Figure 6), the damage patterns of each group of specimens were analyzed as follows:  
Figure 6: \(Cont.\)For the ultra-weakly bedded sandstone, the rupture patterns were similar at \(\theta=0^{\circ}\) and \(15^{\circ}\). Advanced cracks occurred on the bedding plane, and multiple secondary cracks were generated along the bedding plane. The primary cracks started from the middle matrix part at the bottom of the specimen and expanded toward the loading point, but the secondary cracks led the primary cracks to migrate along the bedding surface, and the crack expansion path eventually showed an intermittent step pattern. Therefore, the rupture mode was a mixed type of tension rupture with mainly through-layer tension rupture, accompanied by the migration of the main crack along the bedding surface. When \(\theta=30^{\circ}\), \(45^{\circ}\), \(60^{\circ}\), \(75^{\circ}\), or \(90^{\circ}\), the layered surface will also rupture superficially, and multiple cracks along the layered surface will appear. With the loading of displacement, these cracks interact with one another; that is, the cracks in the rock body fracture competitively with one another, and eventually the crack at a certain layer \"win\" becomes the main crack and expands until the end of the damage. When \(\theta=30^{\circ}\), the crack expands mainly along the \(30^{\circ}\) bedding plane, but localized penetration rupture occurs in the process. Therefore, the damage mode is dominated by the tension rupture along the bedding surface, and local tension rupture through the layers is produced. At other angles, the cracks expand along the bedding plane until the end of the damage, so the entire damage mode is tension rupture along the laminae. In the case of weakly bedded sandstone, the damage patterns are similar for \(\theta=0^{\circ}\), \(15^{\circ}\), \(30^{\circ}\), and \(45^{\circ}\). Advanced cracks still occur on the bedding plane, but they are not as obvious as when the bedding strength is 0.3 times, and the guiding effect of secondary cracks on the main crack is obviously weakened. The damage model is still a mixed type of tension rupture with mainly tension rupture through the plies, accompanied by the migration of the main crack along the bedding plane. With the increase in the bedding inclination angle, the extension direction of the main crack tends to be more vertical. When \(\theta=60^{\circ}\), the damage mode is mainly tension rupture along the bedding plane, and the transbedding tensile fracture occurs locally. When \(\theta=75^{\circ}\) and \(90^{\circ}\), the crack completely develops a tensile fracture along the bedding plane. In the case of the strongly bedded sandstone, the damage pattern of each laminated dip specimen is very similar to that of the homogeneous sandstone, which shows that the strength and dip angle of the bedding have little effect on the damage pattern of the  
Figure 6: Cloud images of different sandstone fracture modes. specimens at this time, and the damage patterns that occur are essentially the same, with all of them being tension rupture through the layers in the direction of the loading point. Among them, when the bedding angle is \(30^{\circ}\) and \(60^{\circ}\), there is a great difference between the fracture trajectory of homogeneous sandstone and the fracture trajectory of the two in the form of \"symmetry\". These two bedding angles lead to relatively active offset fractures and frequent shear fractures, leading to a large offset of the main fractures, similar to ultra-weak sandstone.