Hydrophilic characteristics of soft rock in deep mines

A series of water absorption tests on dried soft rock have been conducted by the intelligent testing system for water absorption tests in deep soft rock, including tests of water absorption with and without pressure. The results show that the water absorbing capacity of rock with a certain pressure is larger than that of rock without pressure; however, the relationship between the water absorbing percentage and the time can be expressed by w(t) = a(1 − e-bt). In bi-logarithmic coordinates, the hydrophilic relationship with time in tests with pressure could be characterized by linearity, while they present concave or convex in tests without pressure. Based on the hypothesis that each influential factor is irrelevant and they have a linear correlation with the water absorbing capacity, we calculated the weight coefficient of each factor according to experimental results under different conditions. The calculations demonstrate that the effective porosity, content of smectite and kaolinite are all positively correlated with the water absorption capacity of rock; meanwhile, the fractal dimension of the effective pores presents a negative correlation with the water absorption capacity of rock. The water absorption capacity with pressure increases with increasing illite, chlorite and chlorite/smectite formation and a decrease in illite/smectite formation and the fractal dimension of the effective pores, while it is opposite in tests without pressure. The weight coefficient of smectite is smallest among positive factors, and the fractal dimension of the effective pores is the smallest amongst the negative factors.