Simulation of Water-Resistance of a Clay Layer During Mining: Analysis of a Safe Water Head

Given previous research and prototypical geological conditions of a mining workface, we simulated fissure development in clay layers at the bottom of Quaternary strata and above bedrock, sand and water inrush during mining by model experiments. The results show that V-shaped fissures usually occur in the bottom clay layer at the front top of the active face and that the position of these fissures changes periodically with ground pressure intervals. These fissures occur exactly in the area where the horizontal strain is concentrated. The results also demonstrate that the permeability coefficient of the cracked clay decreases while fissures tend to close. The permeability of the cracked bottom clay layer increases rapidly after a turning point in the permeability coefficient-water head curve (K-H curve) under a certain vertical load. Under static water pressure, the permeability coefficient of cracked clay decreases when load increases. A turning point in the K-H curve showed up and can be seen as a cutoff point to decide water inrush under a certain load level. Under an instantaneous water head, the greatest ability of the cracked clay to avoid drastic water inflow is a little higher than that under static conditions.