The mixed backfill paste for subsidence area is a kind of artificial compound granular media which has wide size fraction and is made of unclassified tailings and waste rock; its permeability performance directly affects the stability of backfill body for subsidence area and other secondary disasters occurrence. Based on homemade experimental apparatus of permeability

the effects of the content of waste rock

waste rock particle size on permeability coefficient of mixed backfill body

and the relevance between backfill paste’s inherent characteristic parameters (the content of particle size below 0.075 mm and 0.02 mm

non-uniform coefficient

mean particle size) and permeability coefficient are studied. Test results show that

with waste rock content and particle size increasing

the permeability coefficient of backfill paste increases; the fine particle effect is remarkable. The content of particle size below 0.075 mm and 0.02 mm in backfill paste has a crucial effect on permeability and has a negative exponent relation with the permeability coefficient. Permeability coefficient increases along with the values. When the value is less than 20

permeability coefficient increases sharply; and when the value is greater than 20

the increase in permeability tends to be stable. Then the quantitative equation of mixed backfill paste permeability coefficient is obtained

which is consistent with the test results.