Experimental Research on the Mass Transfer and Flow Properties of Water Inrush in Completely Weathered Granite Under Different Particle Size Distributions

Water inrush disasters originating from completely weathered granite are strongly affected by its physical and mechanical properties, such as the porosity, permeability, and water stability. The porosity and permeability are heavily affected by the particle composition. Meanwhile, a large amount of particles with poor cementation, are transferred by water, which may affect the flow properties and water inrush. This study investigates the mass transfer and flow properties of water inrush in completely weathered granite for different particle size distributions. To this end, a series of tests was performed by designing a new testing system, which can induce mass transfer and apply external pressures during the tests. The results demonstrate the following: (1) the flow properties and water inrush are related to the mass transfer. In the experiments, it was found that the permeability of the samples increases by a factor of 14–53.3, compared with the initial permeability. Thus, a notable signal to forecast water inrush can be obtained, which represents the change in water quality from muddy water to clear water. (2) With an increase in Talbot index n, the mass transfer and porosity first decrease and then increase. However, the permeability and water inflow increase and a critical value of n = 1.0 is required to induce the water inrush. (3) Three flow stages, namely, a Darcy flow, rapid flow, and stable flow, can be utilized to describe the water inrush evolution. Non-Darcy flow properties and high water inrush risk are observed in the second stage, where the water inflow increases to 551 mL/min, which is more than thrice that in the Darcy flow for n = 1.0. The obtained results can provide an important reference to understand the mechanisms, forecast the risks, and implement effective control measures for water inrush (e.g., optimum control time).