Experimental research on the effect of particle migration of a filling medium in a fault during water and mud inrush

The water and mud inrush due to particle migration of a filling medium in a fault is a common disaster in tunnel engineering. To study the hydraulic properties of the filling medium during the water and mud inrush such as the total mass of flushed particles, water inflow, porosity, and permeability, a series of experiments were conducted in a self-designed experimental system under different water pressures, clay contents, and filling medium dry densities. The results showed that particle migration played an important role in increasing the porosity and permeability of the filling medium. The process of water and mud inrush can be categorized into three stages: (a) slow flow stage, (b) catastrophic flow stage, and (c) steady flow stage. The change of water clarity from turbid to clear and the constant total mass of the flushed particles can be regarded as precursor information to forecast the water and mud inrush disaster. Furthermore, filling medium with lower clay content, lower soil dry density, and higher water pressure will achieve a higher total mass of flushed particles, water inflow, porosity, and permeability at the completion of the test. These results can help improve understanding of the hydraulic properties of water and mud inrush through particle migration of a filling medium in a fault, thereby improving the forecasting of such events.