Swelling Damage Evolution of Argillaceous Slate in a Water-Rich Environment

The swelling of rock is a key issue in engineering. With large infrastructure construction trending toward complex geological conditions, an increasing number of projects could suffer from soft rock swelling. To solve this problem, an understanding of the damage evolution during the swelling process is essential. Argillaceous slate is a typical metamorphic rock and shows strong swelling characteristics in a water-rich environment due to its abundance of hydrophilic minerals. In this paper, argillaceous slate was selected as the research object. The damage evolution of argillaceous slate during swelling was explored via laboratory tests including swelling characteristic tests, soft rock needle penetration tests, and scanning electron microscope tests and damage theory. The research findings reveal that the slate swelling process in a water-rich environment could be divided into three stages. The swelling rate was relatively high in the early stage of the tests, slowed over time, and finally stabilized. However, the argillaceous slate strength decreased rapidly in the early stage, and the degradation rate was generally slow in the later stage. After water absorption, the clay mineral particles began to expand, and the microscopic structure of the argillaceous slate became complicated. The pore area increased, and the pore diameter decreased. A low degree of microscopic damage induced a high degree of macroscopic mechanical degradation. Additionally, the damage mechanism of argillaceous slate during swelling was discussed from micro- and macroscopic perspectives. A relationship between macroscopic mechanical degradation and microscopic damage to argillaceous slate was established, which can provide theoretical support for further research on soft rock swelling characteristics: The microscopic damage drove the macroscopic mechanical degradation.