Experimental research on water retention effect and shear resistance of water-retaining materials in open-pit mines

The large-scale mining of coal resources and high-intensity mining operations, especially open-pit mining, large-scale surface excavations have caused serious vegetation degradation and soil erosion. Water retaining materials have received more and more attention in the water-retaining and reclamation technology of open-pit mines. Through the water retention effect test of the water retention material, the water absorption and release characteristics of the water retention materials were summarized, and the Electrical Conductivity (EC) value and the pH value of the water retention reclaimed soil materials of different proportions were summarized, and the EC value and the pH value change law were analyzed. Based on the direct shear test, the relationship between the cohesion, the angle of internal friction and the content of the water-retaining reclaimed soil material was revealed. The tests show that the water-retaining soil materials mixed with water-retaining materials of 60-100 meshes have better water-holding effects. Under the conditions of normal temperature and drying, the water-retaining materials with different mesh numbers had almost the same water release rate difference, and the amount of water released was almost the same. As the test time increases, the EC values of 0.1% and 0.33% water-retaining reclaimed soil materials gradually decreases and are lower than 0.2. While the EC values of 0.50% and 1.00% show an overall increasing trend and appear obviously at 84 h, the pH value gradually increases, and the 0.50% pH value increases more moderately. The shear strength first increases and then decreases with the increase of the water-retaining material content. The cohesive force gradually decreases with the increase of the water-retaining material content, and the internal friction angle first increases and then decreases with the increase of the water-retaining material content. When the mass fraction exceeds 0.50%, the cohesive force decreases faster, but the internal friction angle reaches the maximum value of 19.00°. Under the condition that the cohesion is not much different, the internal friction angle of the water-retaining material with a mass fraction of 0.50% is larger than that of the others, and the shear resistance of the water-retaining and reclaimed soil material is better.