###### Abstract  
The fracture characteristics of bedded sandstone determine the stability and safety of in situ coal gasification technology. Four semicircular stratified sandstone specimens with different strengths (0.3, 0.6, 1.0, and 1.5 times that of rock matrix) and seven different bedding angles (0 = 0\({}^{\circ}\), 15\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), 75\({}^{\circ}\), and 90\({}^{\circ}\)) were numerically simulated using RFPA2D-Basic V2.0 software. The SCB specimen had no prefabricated crack, and its radius was 25 mm. The loading rate was 0.00001 m/step. The results show that the fracture characteristics of the sandstone are affected by both the strength of the laminae and the angle; the fracture toughness and peak strength of the ultra-weak sandstone, as well as the weak sandstone, are reduced and more easily affected by the bedding angle; the strength rate of the strong sandstone is higher than that of the homogeneous sandstone, and the difference between the fracture characteristics of the two is not significant. This paper suggests that the key mechanism of this phenomenon is the anisotropy between the bedding and the sandstone, along with the competition/synergy between the main crack and the bedding plane bias crack during fracture propagation. These research results can provide a theoretical reference for the safety and stability of underground engineering in China. s +
Footnote † † † †: The research results of this paper can be used as the theoretical basis for further development and application of coal in situ gasification technology. Footnote †surrounding coal and rock mass, but if the gas cannot smoothly penetrate into the outlet pipeline, it may diffuse and penetrate into other surrounding rocks, causing environmental pollution [4]. In the process of coal pyrolysis and gasification, the movement of gas is mainly controlled by the permeability and mechanical properties of the surrounding coal and rock mass. The fracture properties of layered rock mass, as shown in Figure 1, are divided into two main parts: mechanical properties, and crack propagation behavior [5]. Among them, the mechanical properties of layered rock have been studied by scholars. [PERSON] et al., (2007) conducted direct shear tests on three specimens of layered salt rock without an interlayer, pure hard gypsum, and laminated salt rock with a hard gypsum interlayer, and they obtained the shear strength parameters of the three specimens, finding that the shear strength parameters at the intersection of the hard gypsum interlayer and salt rock were slightly stronger than those of the pure laminated salt rock and pure hard gypsum specimens [6]. To investigate the effects of different test conditions on shale crack extension, [PERSON] et al., (2008) considered the laminar dip angle, the height-to-width ratio of the specimen, and the rate of test loading, and the elastic modulus and compressive strength of the shale both decreased and then increased with the increasing angle between the laminar surface and the loading direction, while the length of the main crack increased and then decreased [7]. [PERSON] et al., (1996) conducted uniaxial and triaxial tests on four types of schist and analyzed the variation of strength and deformation anisotropy with the dip angle and confining pressure in detail [8]. [PERSON] et al., (2014) studied the peak strength and deformation characteristics of layered sandstone with different bedding dip angles in dry and saturated states, and they analyzed the energy dissipation characteristics of the sample under loading deformation and failure by using the monitored acoustic emission data [9]. [PERSON] et al., (2018) found that the mechanical properties of layered sandstone under static loading showed significant differentiation with the change in the dip angle [10].