Reconstruction of aquifuge:The engineering geological study of N2 laterite located in key aquifuge concerning coal mining with water protection in northwest China

In the arid-semiarid area of northwest China,the shallow water such as the water of rivers and lakes,valley runoff water,the phreatic water of Quaternary in sand-layer and so on are precious water resources which maintain re- gional ecological geological environment and the body of water resource protection in coal mining. According to the re- gional geological structure of the shallow water aquifer-aquifuge,the N2 laterite,distributed widely above coal seam in northwest coal field of China,as the direct aquifuge bottom of regional shallow water or valleys runoff cushion,playing a crucial role to the coal mining with water protection and ecological environment protection,is the key aquifuge soil. In this paper,based on the analysis of regional distribution features,the basic physical,hydro-physical and the me- chanical properties of N2 laterite,the impermeability of post-mining stress recovery creep,before mining crack and post mining was deeply studied and analyzed by the water pressure test before and after mining,the test of creep permeabil- ity and the experiment of soil-water interaction and so on. The results show that the N2 laterite has a good capacity of self-recovery after the impermeability was broken by mining crack. The mechanism of impermeability self-recovery was explained from the perspective of geological structure,soil-water interaction and rheological properties;and according to this finding,the reconstruction of aquifuge and major engineering geological properties included was proposed.