Experimental Study on Permeability of Mining-Cracked N₂ Laterite

The laterite of Neogene pliocene series （N₂）, abbreviated as N₂ laterite, over coal seams distributed widely in the mining area of western China is the key aquifuge soil for protecting the shallow water from being destroyed by coal mining. The permeability change induced by soil-water interactions of mining-cracked N₂ laterite was studied. On the basis of analyzing the mineral composition and swelling properties of N₂ laterite, the water inrush evolution process induced by soil-water interactions of mining-cracked N₂ laterite was studied quantitatively using self-made experimental equipment. The results show that there is a high content of hydrophilic minerals in the clay minerals of N₂ laterite, such as montmorillonite and illite/montmoduonite interstratified, therefore N₂ laterite is more hydrophilic and has strong expansionary. During the early stages of soil-water interactions of mining-cracked N₂ laterite, the accumulation of loose particles and the collapse of fracture edges were more intense, and the degree of fracture closure was larger. In the 100 minutes of the whole water inrush test, the amount of crack closure in the first 15 minutes accounts for about 60% of the total closure degree. In addition, the change of water inrush volume can be divided into three typical stages, namely, the rapid decline stage, the slow decline stage, and the stable stage. The greater the crack width is, the longer the water inrush stability time. The relationship between the permeability induced by soil-water interactions of mining-cracked N₂ laterite and time is a negative exponential relationship.