# Experimental Study on Mechanical Properties of Anisotropic Slate under Different Water Contents
###### Abstract  
Slate typically possesses a pronounced layered structure and tends to soften when exposed to water, leading to numerous detrimental effects on the construction of related underground projects. In this study, X-ray diffraction (XRD) analysis was first performed to investigate the mineral composition of the typical slate from Changsha, China. Then, uniaxial and triaxial compression tests under varying bedding angles (i.e., \(0^{\circ}\), \(30^{\circ}\), \(45^{\circ}\), \(60^{\circ}\), and \(90^{\circ}\)) and moisture levels (i.e., dry state, natural state, and saturated state) were conducted to explore the anisotropy characteristics and susceptibility to water-induced softening of the slate. The results reveal that: (1) The exposure of slate to water exacerbates the deterioration of its layered structure, making it more prone to shear failure along the bedding planes. Furthermore, the energy released during shear-slip damage is reduced, which is macroscopically manifested by the decrease in slate brittleness and the increase in plasticity. (2) The slate's compressive strength, elastic modulus, and cohesion vary in a U-shaped pattern with the increase in bedding angles. However, Poisson's ratio and internal friction angle are slightly affected by the bedding angle and water content, which do not exhibit a clear variation pattern. (3) In addition, the formulations for strength and stiffness predictions of slate were also discussed in this study. The results show that the modified Hoek-Brown criterion characterizes the uniaxial and triaxial compressive strengths of slate more accurately, and the generalized Hooke's Law more effectively predicts the elastic modulus. slate; varying moisture levels; uniaxial compression test; triaxial compression test; anisotropy; failure modes +
Footnote †: journal: Medical Sciences  
0000-0001-9001-9000][PERSON]  
0000-0001-9001-9001-9000][PERSON]  
0000-0001-9001-9001-9001-9000][PERSON]  
0000-0001 uniaxial compression and Brazilian splitting tests on rocks with three different bedding angles, reported that when the bedding plane is tilted relative to the loading direction, the influence of weak planes becomes more evident, and the strength anisotropy exceeds the elastic modulus anisotropy. [PERSON] et al. [5] conducted a dynamic compression test on anisotropic rock masses and discovered that under the same strain rate, the dynamic compressive strength of the anisotropic rock masses varies in a U-shaped pattern with the increase in bedding angle; the trend becomes more pronounced with higher strain rates. [PERSON] [6] monitored the slate fracture process, identifying that the bedding angle and microscopic strength anisotropy in the bedding direction are key factors affecting the macroscopic strength anisotropy of the sample. [PERSON] et al. [7] focused on the microscale parameters of sandy slate, highlighting that the number of bedding planes, weak mineral content, and polycrystal grain size are the main factors influencing the macro-mechanical properties of slate. [PERSON] et al. [8], [PERSON] et al. [9], and [PERSON] et al. [10] indicated that slate bedding planes significantly impact the deformation characteristics, failure mode, and strength parameters of rock based on a mechanical test of slate. These studies primarily explore the anisotropic properties of foliated rocks and slates from different bedding directions, elucidating relevant physical and mechanical properties. However, most studies focus on a single variable, with few examining the changes in failure modes and anisotropic properties of foliated rocks. Under water-rich conditions, foliated anisotropic rocks' physical and mechanical properties are greatly affected, resulting in noticeable softening and deterioration. [PERSON] et al. [11], based on ultrasonic velocity measurement results of shale, reported that with increasing water content, the transverse and longitudinal wave speeds decrease, and the anisotropy increases.