Background The Muli mining area is an indispensable water conservation area and the core component of the ecological security barrier in the Qilian Mountains, and its ecological status is extremely important. However, with a large number of excavations, the Muli mining area has accumulated large-scale coal gangue piles. The weathering deposits on the surface of these coal gangue slopes cause preferential flow, resulting in a series of ecological and environmental problems such as soil damage, soil erosion, and slope instability. In order to solve the above ecological and environmental problems, this paper chose Muli mining area as the research area.

Methods In view of the insufficient research on the actual effect and key influencing factors of polyurethane solidified coal gangue, this study carried out 45 groups of uniaxial compression tests of coal gangue-polyurethane solidified specimens with different proportions, and 60 groups of artificial rainfall tests of coal gangue-polyurethane solidified slopes under different working conditions. The main mechanical properties, permeability and technical economy of coal gangue-polyurethane composites were studied. The analytic hierarchy process was used to comprehensively evaluate different mix ratios, and to reveal the key influencing factors, and screen the optimal mix ratio scheme.

Results 1) Polyurethane concentration contributed the most to improving the compressive strength of the solidified specimens, while the elastic modulus was mainly affected by the particle size of coal gangue. 2) The average runoff rate of solidified coal gangue slope was proportional to the concentration of polyurethane, proportional to the density of coal gangue, and inversely proportional to the particle size; the average sediment yield was inversely proportional to particle size of coal gangue, density of coal gangue and polyurethane concentration. The stable infiltration rate was proportional to the particle size of coal gangue, and the density of coal gangue was inversely proportional to the polyurethane concentration and inversely proportional to the density.3) The comprehensive evaluation of 45 groups of coal gangue-polyurethane curing schemes was carried out. When the particle size was 0-0.5 mm, the comprehensive evaluation value was 0.260 68-0.725 35. When the particle size was 0.5-1 mm, the comprehensive evaluation value was 0.313 86-0.442 87. When the particle size was 1-2 mm, the comprehensive evaluation value was 0.266 33-0.311 14.

Conclusions The optimal slope stabilization scheme is coal gangue with the particle size 0-0.5 mm, the density 1.55 g/cm³, polyurethane concentration 3.5% The coal gangue-polyurethane curing scheme may greatly improve the compressive strength of the slope, and effectively reduce the infiltration performance, while maintaining a good economy (about 17 RMB Yuan/m²). The research results have important technical reference for the ecological restoration project of Muli Coal Mine.