Experimental study on permeability of crushed gangues during compaction

• We designed a crushed rock compaction permeation apparatus and a seepage circuit.
• We test the permeability of crushed gangues with six different particle sizes.
• We analyze the relationship between pressure gradient and seepage velocity.
• We analyze the relationship between permeability and porosity.
• We analyze the relationship between non-Darcy flow β factor and porosity.

Using a crushed rock compaction permeation apparatus and a self-designed seepage circuit, we tested the permeability of crushed gangues with six different particle sizes during compaction on the CMT5305 electronic universal testing machine and analyzed the relationships of seepage velocity, permeability and non-Darcy β factor to the porosity, particle size and diameter distribution. The results show that 1) The seepage flow of crushed gangues during compaction is nonlinear, and their compactability after compaction is related to their final porosity; 2) the seepage velocity of crushed gangues of same size decreases with pressure gradient increase and with porosity decrease, and varies less than that of crushed gangues of same porosity and mixed size or size between 10 and 15 mm. Moreover, the greater the single particle size is, the greater the pressure gradient. In addition, the mixed gangues have the lowest pressure gradient; 3) the permeability of gangues of same size decreases with their size increase and that of the mixed gangues is the largest; 4) the relationship of permeability to porosity can be divided into two stages with porosity decrease. At the stage II, permeability decreases significantly by the magnitude of 2 to 3 compared to that at the stage I. After stage II, the permeability of crushed gangue decreases to the magnitude of 10− 15 m2, while the impermeability increases; 5) the non-Darcy β factor is negative for gangues with size larger than 10 mm, while that gradually becomes positive with porosity decrease for mixed gangues and gangues with size less than 10 mm. Moreover, non-Darcyβ factors affect the impermeability of gangues. The results will provide references for gangues as filling materials.