关键词: 巴西劈裂, 抗拉强度, 细观结构, 层理

Abstract:

The stability of rock structures plays a crucial role in various mining processes, including the study of open-pit mine slopes, predictive analyses of mine pressure in roadways, and the stability of underground quarries. Consequently, research into the strength and stability of rocks has remained a prominent area of focus in mining engineering. Numerous studies in rock mechanics have shown that the tensile strength of rock is significantly lower than its compressive strength, with most rock failures resulting from cleavage damage. As such, tensile strength is a key indicator of rock integrity. Current research on the tensile strength of laminated rocks primarily investigates the relationship between tensile strength and lamina inclination, with little attention paid to the influence of lamina spacing. Additionally, studies often describe the relationship between tensile strength and lamina inclination without exploring the underlying microstructural mechanisms responsible for rock failure. This study aims to investigate the relationship between tensile deformation characteristics, lamina spacing, and loading direction. Experimental samples were prepared with lamina spacing of 2d, 23/3d, d on the cuts of S₁, S₂, S₃ surface and level S, respectively. Brazilian splitting tests were performed to determine the tensile strength of siltstone under different loading directions. Full-field strain measurements using Digital Image Correlation(DIC)were employed to observe the deformation characteristics, and microstructural analysis was conducted based on crystal space distribution theory.

The results of the experiments are as follows:

(1)When the loading direction is parallel to the lamination direction, the tensile strengths of the S₁(2d), S₂(23/3d), and S₃(d) surfaces are 29.99MPa, 26.56MPa, and 18.92MPa, respectively. When the loading direction is perpendicular to the lamination direction, the tensile strengths of the same surfaces are 32.76MPa, 30.44MPa, and 27.77MPa. These findings indicate that tensile strength decreases with decreasing lamina spacing. Thus, as the laminae become more closely spaced, the tensile strength weakens, highlighting the contact surfaces between laminae as weak planes.

(2)The tensile strength of the sample with the S surface as the layer is not primarily influenced by weak interfaces, but rather by the mineral arrangement within the layer. When the loading direction aligns with denser mineral arrangements, the sample is more prone to cracking along the direction of looser particle arrangements, resulting in lower tensile strength. This demonstrates that preferential mineral orientation significantly impacts tensile strength.

(3)For samples with the same lamina spacing, when the loading direction is parallel to the laminae, the tensile region is concentrated along the centerline of the sample. As loading progresses, the tensile region propagates, eventually causing the sample to split into two. When the loading direction is perpendicular to the laminae, the tensile region is more dispersed initially, with several strain concentration points. These points are typically located along the transverse axis, and the sample splits in a manner similar to the parallel loading case. When the loading direction is diagonal to the laminae, the distribution of tensile regions is irregular, with the weak contact positions between laminae contributing to intermittent and tilted strain distributions.

(4)As lamina spacing decreases, the concentration of strain zones becomes denser under the same loading direction, further supporting the hypothesis that laminae contact surfaces act as weak planes.

The above findings provide valuable insights into the tensile behavior of laminated rocks and the influence of lamina spacing and mineral arrangement on rock strength.

Key words: Brazil split, tensile strength, mesostructure, layering