Study on Seepage and Stability of Soft Rock Slope with Fissures Under Extreme Rainfall

Extreme rainfall can lead to instability of fissured soft rock slopes. In this study, under the background of Nanfen open-pit mine slope, the seepage characteristics of slope fissured rock mass under extreme rainfall and the influence of seepage and rock softening factors on slope stability were investigated through numerical simulation. The pore water pressure and safety factor in the slope without drainage measures and with drainage holes were compared. As revealed by the results, the fissure depth was positively correlated with the rainfall infiltration depth and range, the fissure angle was negatively correlated with the rainfall infiltration depth, the fissure spacing was negatively correlated with the rainfall infiltration range and the size of the slope saturated area, and the permeability coefficient ratio was positively correlated with the rainfall vertical permeability. In the early stage of extreme rainfall, the slope stability was mainly reduced due to fissure seepage, with the duration of rainfall, the influence of softening of soft rock on the slope safety factor gradually increased, and at the end of rainfall, the decrease of fissure seepage and rock softening factors on the slope safety factor was 22.3% and 24.2%, respectively. In the process of extreme rainfall, the safety factor of slope could be kept above 1.11 by using inclined drainage hole slope drainage, which was 21.6% higher than that without drainage hole. The research results can provide a reference for the stability analysis and landslide control of soft rock slope with fissure development under extreme rainfall conditions.