The holes in the flat or gentle slope should be first removed and the soft rocks in the holes should be cleaned with high pressure wind or high pressure water, and then the concrete should be backfilled. When the width and depth of the holes are less than 500mm, the grade20/19 concrete should be used. When the orifice width and depth are greater than 500mm, Grade20/38 concrete is used. Backfill concrete surface slope should be consistent with the base surface, concrete surface should be punched or chiseled.