Background  Coal gangue is a solid waste generated in the process of coal production, which has low water-retaining capacity. A large amount of coal gangue accumulation may cause serious environmental pollutions. At present, the main way to treat gangue mountains is to directly cover soil and vegetation reconstruction; however, usually the mining area is short of soil and the site condition is extremely adverse. Therefore, it is necessary to add different proportion of coal gangue and water-retaining agent in soil to make rational use of coal gangue and improve its water-retaining property.

Methods  Yangchangwan dump site of Lingwu in Ningxia Hui Autonomous Region was taken as the research object, and 3 types of gangue matrix were set up:the ratio of coal gangue to soil was 3:1(CGM₁), 1:1(CGM₂) and 1:3(CGM₃). In addition, acrylamide-potassium acrylate crosspolymer type (CLP) and attapulgite composite acrylamide-acrylamide type (WT) water-retaining agent with ratios of 0.1%, 0.2% and 0.5% were added respectively. The porosity, water absorption, water-retaining capacity and infiltration of gangue matrix were determined by soil column simulation.

Results  1) The porosity, water-holding capacity and cumulative infiltration of CGM₂ and CGM₃ were higher than those of CGM₁. With the increasing of proportion of CLP and WT, the water absorption and water-holding capacity of these treatments showed an increasing trend. The addition of CLP promoted soil water infiltration, and with the increasing of the proportion, its promotion effect became more obvious. However, the addition of WT was inversely proportional to the cumulative infiltration of coal gangue matrix. In CGM₂, the adding proportion of 0.5% CLP had the highest cumulative infiltration at 60 min, reaching 48.78 mL. 2) A multi-way ANOVA demonstrated that the type of coal gangue matrix was the main factor affecting the water-holding capacity of the matrix, and the type of water-retaining agent had the greatest influence on the cumulative infiltration of coal gangue matrix. 3) Cluster analysis was performed on 21 treatments, which were divided into 3 groups. Group Ⅲ only included treatment adding 0.5%CLP under CGM₂, which had better water retention and infiltration characteristics than those of other treatments.

Conclusions  Adding water-retaining agent can improve the water retention performance of coal gangue matrix. The best water retention effect is obtained when 0.5% acrylamide-potassium acrylate crosspolymer added to the ratio of coal gangue to soil 1:1.