"Iron Ion Relative Weathering Index": A New Index for Identifying the Weathering Degree in Red Sandstone.

The red bed region in west central and southern China is affected by hot and humid climate, where sandstone is intensely weathered. The weathered hazardous rocks seriously threaten the road and slope, making it challenging to protect the Danxia red bed. After considering the red sandstone's material composition and the local area's main weathering effects. We noticed that iron ions in red sandstone are susceptible to weathering, which leads to changes in the valence and content of iron ions. This study attempts to establish a new chemical weathering index called the "iron ion relative weathering index" (IRWI) to classify the weathering degree of red sandstone. This paper mainly explores the changes of physical characteristics (mineral composition, physical indicator, microstructure, and pore structure) from the surface to the interior of red sandstone in the actual environment and their correlation with IRWI. The study on the correlation between the physical indicators such as longitudinal wave velocity, resistivity, density, water absorption, and IRWI reveals that they have the same trends and are closely related to the weathering degree. The shallow weathering zone of Chishui red sandstone is divided into strong, medium, and slight weathering zones. Microscopically, the cementation and pore distribution of the red sandstone are consistent with the characteristics of the weathering zone. Therefore, IRWI not only is a reliable chemical quantitative method in indicating the weathering of red sandstone but also takes into account the controlling role of iron in the color development of red beds, which provides a new research idea for the quantitative identification of weathering degree and color mechanism of red sandstone.

Study on Failure Mechanism and Numerical Simulation of Argillaceous Slate in Southeastern Guizhou.

The content of quartz and clay minerals has a crucial influence on the mechanical properties of slate, which is manifested by the differences in microscopic displacement and energy conversion during uniaxial compression. With Qiandongnan argillaceous slate in Guizhou Province as the research object, the parameters for numerical simulation were determined through indoor uniaxial tests, and argillaceous slate models with different mineral contents were established to analyze crack formation and energy conversion during uniaxial compression. The damage rate of the specimen was qualitatively analyzed by the fractal dimension of the crack. The results show that ① the number of fractures increases with the increase of quartz content, and the number of cracks in Group 4 is 33.4% higher than that in Group 1, and macroscopic fractures are dominated by cracks while microscopic fractures by tension fractures, accompanied by a small amount of shear; ② the energy change curves of the four groups of specimens are consistent with the stress-strain curves, which are divided into three stages, namely elastic deformation, yield, and strength loss. The strain energy in the strength loss stage is negatively correlated with the dissipated energy, and the dissipated energy of the four groups of specimens is positively correlated with the content of quartz; ③ the damage rates for the specimens in Groups 1 to 4 quantitatively analyzed using fracture fractal dimension are 56.8, 59.1, 65.8, and 70.7%, respectively. The research results obtained in this article have further improved the failure mechanism of argillaceous slate under uniaxial compression.