Model experimental study on the seepage of overburden soil layers above fractured rockmass due to coal-mining

Concrete blocks with fissures of different sizes are adopted to simulate mining fractured rock mass,and the clay,silt,coarse sand and gravel are used to compose 21 kinds of soil samples with different particle size distributions.Then,the types and mechanisms of the seepage deformation and failure of the unconsolidated soil layers across the caving zone and water flowing fractured zone within overburden,and the relationship between the critical percolation gradient of unconsolidated soil layers while seepage failure across mining-induced fissures from above to bellow vertically,soil particle size distributions,physical and mechanical properties and the widths of fissures are studied in laboratory tests by reequipped seepage meters.The results show that the silt,coarse sand and gravel with small amount of clay are easier to quicksand.The wider the fissures are,the smaller the critical percolation gradient for the same soil sample is when seepage failure deformation occurs across fissures,and the critical percolation gradient decreases exponentially with the extension of the width of fissures.So it can be deduced that the width of fissures are the key factors controlling the amount of the quicksand.