Abstract: The hydraulic characteristics of slag in dump are the key factors affecting the stability of slope and the development
of post-construction settlement. At present,there is still a lack of systematic understanding of the hydraulic characteristics
of slag materials in compacted state. Taking the slag of an open-pit mine dump as the research object,the saturated permeability
coefficient and soil-water characteristic curve of slag under different compaction conditions were measured by variable
head permeability test and pressure plate instrument test,and the unsaturated permeability coefficient was predicted based on
the Childs & Collis-George model. It is found that with the increase of dry density of slag,its pore structure tends to be dense,
resulting in a significant decrease in saturated permeability coefficient. When the dry density of slag increased from 1. 50
g/ cm3 to 1. 90 g/ cm3,the permeability coefficient decreased by 99. 63%. Under the same matric suction,the higher dry density
sample has stronger water holding capacity,and its soil water characteristic curve can be well fitted with the Van Genuchten
model,and the correlation coefficient can reach more than 0. 996. The saturated permeability coefficient decreases with the increase
of dry density. When the dry density increased from 1. 60 g/ cm3 to 1. 80 g/ cm3,the permeability coefficient decreased
from 2. 0×10-4 cm/ s to 7. 0×10-5 cm/ s. And it decays in power function with the increase of matrix suction. When the suction
increases from 0. 01 kPa to 400 kPa,the permeability coefficient decreases by three orders of magnitude. This study reveals the
influence mechanism of compaction degree on the hydraulic characteristics of slag from the perspective of microscopic pore evolution
and macroscopic hydraulic response. It is suggested that the seepage stability of dump can be optimized by controlling the
compaction quality in practical engineering. The research results can provide theoretical support and practical guidance for
dump slope design and long-term safety assessment.