In order to confirm the impact of the loading history on the permeability characteristics of broken coal

the permeability characteristics of broken coal with different grain size gradations are tested under two experimental schemes by the CMT5305 electronic universal testing machine with a seepage circuit which is composed of gear pump

reversing valve

overflow valve

permeameter

etc. And the relations between the seepage velocity

permeability

the non-Darcy flow ? factor and the porosity are obtained under the two experimental schemes. The experimental results show: ①The power function fits the relationship between the seepage velocity

permeability and the porosity in the first experimental scheme; and exponential function fits the same relationship in the second scheme. ②When the porosity is large

the permeability and the non-Darcy flow? factor bear a relation to the loading history

while when the porosity is small

they tend to be stable and are independent of the loading history. ③With the decrease of the porosity

the non-Darcy flow ? factor changes from negative to positive in the first scheme; and the permeability characteristics of the broken coal with different grain size gradations are strengthened; but the non-Darcy flow ? factor is always negative in the second scheme and the permeability characteristics are weakened. ④Relation between the non-Darcy flow ? factor and the porosity can be fitted by the cubic polynomial

of which the coefficients have connections with the loading history.