[Objective] The physical properties of topsoil substitute materials formed by overburden materials in the open-pit coal mine with different ratios were explored

in order to provide a theoretical basis for the development of topsoil substitute materials and comprehensive utilization of stripping materials in open-pit coal mines.[Methods] Taking the stripping material of an open-pit coal mine in Eastern Inner Mongolia as the research object

the bulk density

porosity

field capacity

particle size

specific surface area and composition of topsoil substitute materials were determined by cutting ring method

laser particle size analyzer and X-ray fluorescence spectrometry. The relationships between physical properties of topsoil substitute materials were analyzed by the grey relational analysis and principal component analysis

and the core indexes affecting the physical properties of topsoil substitute materials were analyzed to obtain the most appropriate ratio of topsoil substitute materials.[Results] ① The two important indexes affecting the physical properties of topsoil substitute materials were bulk density and maximum field capacity

while the main indexes influencing the field capacity were specific surface area and total porosity of particles. ② The increase of the proportion of heart soil (Calcium layer soil) and fine sand by 30%

would lead to the decrease of the field capacity of topsoil substitute material by 22%. ③ Diameter span and D10 were the key indexes determining the bulk density of topsoil substitute materials. ④ 5A (lower mudstone:upper mudstone:floor soil:heart soil:sand=3:3:4:1:2) and 7A (lower mudstone:upper mudstone:floor soil:heart soil:sand=2:1:2:2:2) had better bulk density and field capacity

both of them were the optimal substitute material ratio for the topsoil in this test.[Conclusion] The physical properties of topsoil substitute materials can be effectively improved by adjusting the ratio of overburden materials in open-pit coal mines. In the preparation process of topsoil substitute materials

the proportion of mudstone and floor soil should be increased and the proportion of calcium layer soil should be decreased to strengthen the water holding capacity. The suitable bulk density ratio of topsoil substitute materials formed by overburden materials in open-pit coal mines is mudstone:raw soil:sand=2:2:1.