Abstract: In order to explore the seepage characteristics of fractured rock mass in the shallow silty mudstone slope under different environmental conditions, a self-developed fractured rock mass seepage apparatus was used to conduct seepage tests on fractured silty mudstone samples with six different fracture surface roughnesses (JRC). The seepage characteristics of fractured silty mudstone under different confining pressures and overlying water depths were studied. The results show that the permeability coefficient of silty mudstone is inversely correlated with the confining pressure under different overlying water depths and JRCs, which can be characterized by a power function. The reduction of permeability coefficient can be divided into two stages: a rapid reduction (0? 30 kPa) and a slow reduction (30?50 kPa). CT scanning results confirm the main reason for the decrease of permeability coefficient is that the increase of confining pressure causes the decrease of fracture aperture of silty mudstone. With the increase of confining pressure or the decrease of overlying water depth, the discreteness of fracture permeability coefficient of different JRC silty mudstone decreases gradually. When the confining pressure increases to the maximum and the overlying water depth is the minimum, the effect of JRC on permeability coefficient would be eliminated. It is also found the permeability coefficients of the samples are positively correlated with the overlying water depth under different confining pressures, which can be characterized by an exponential function. Moreover, the nonlinear Izabsh model of seepage flow in fractured silty mudstone is derived, which can better reflect the nonlinear relationship between seepage flow and pressure gradient under low stress and low velocity. However, the correlation of the model decreases with the increase of confining pressure.

Key words: silty mudstone, penetrating fracture, seepage characteristic, low confining pressure, overlying water depth