# Experimental Study on Mechanical Properties of Anisotropic Slate under Different Water Contents
## 3 Experimental Results and Analysis
### Failure Modes and Characteristics  
The failure mode of slate is typically influenced by factors, such as bedding angle, confining pressure, and water content. Different states of the same rock type can exhibit considerable variation in failure mode. As illustrated in Figure 9, the samples are categorized into five groups based on the \(\beta\) value. Each group consists of samples in three distinct states: dry, natural, and saturated. The samples are organized from left to right within each state according to increasing confining pressures: 0, 5, 10 and 15 MPa.  
When \(\beta\) = 0\({}^{\circ}\), the compression direction of the sample aligns perpendicularly to the bedding direction, resulting in a predominantly splitting shear failure that intersects the bedding plane. The angle between the sample's fracture surface and the axial direction diminishes as confining pressure increases but expands with higher water content. Here, the mechanical properties of the slate are primarily influenced by water content and minimally by the bedding plane. The rock's strength largely depends on its inherent properties.  
At a \(\beta\) of 30\({}^{\circ}\), the samples typically exhibit shear failure that cuts through the matrix, with a minority showing shear slip failure along the bedding's weak plane. The fracture surface's development direction is affected by this weak plane, as is the sample's strength. Furthermore, the failure fracture widths are notably narrower in dry and natural states than in saturated states.  
When \(\beta\) = 45\({}^{\circ}\), the quantity of fractures in saturated samples notably exceeds those in dry and natural states, leading to more fragmented rock masses. The dry sample's failure mode involves partial shear failure along the bedding plane. The natural sample displays complete and partial shear failure along the bedding plane, while the saturated sample's failure predominantly follows the bedding plane. As confining pressure increases, the angle between the fracture surface and axial direction generally enlarges in most samples.  
Figure 9: Slate samples failure modes for different \(\beta\) values.  
This suggests that the bedding's weak plane influence intensifies with water content but diminishes with increasing confining pressure.  
When \(\beta=60^{\circ}\), samples with different water contents and varying confining pressures all slip along the bedding plane's direction under compression, forming a shear failure surface in the same direction. Compared to water content and confining pressure, the bedding's weak plane exerts the greatest influence on the \(60^{\circ}\) sample, with its fracture surface primarily controlled by this weak plane.  
At \(\beta\) of \(90^{\circ}\), most samples exhibit a splitting tension failure mode. The load is primarily borne by either the matrix or a combination of the matrix and the weak plane. Hence, the fracture surface typically forms a complex pattern, partially along the weak plane and partially through the matrix. Here, the loading direction aligns with the bedding direction, facilitating the development and coalescence of fractures, especially under load and water-induced softening. However, increased confining pressure compacts the fractures and bedding surfaces within the rock, thereby constraining the sample's splitting failure to some extent. Macroscopically, the number and size of fractures in the sample decrease with rising confining pressure and increase with water content.  
Accordingly, the bedding's weak plane can significantly affect the failure behavior of slate specimens. As the angle between the axial compression direction and bedding direction narrows, the sample's failure mode transitions from shear to splitting failure along the bedding plane. Water content amplification heightens the bedding's weak plane influence on failure mode, while increased confining pressure mitigates this effect. Simultaneously, the number and size of fractures resulting from sample failure escalate with water content and decrease with confining pressure.