Study On Rainfall Seepage Characteristics And Stability Of Open-pit Slope With Gently-inclined Soft Interlayers

In the central and western regions of China,limestone mines in southwestern China generally contain a kind of gently-inclined soft interlayer.Due to its low mechanical strength and poor hydraulic properties,it poses a serious threat to the stability of mine slope under rainfall conditions.In order to explore the rainfall seepage characteristics and stability of the mine slope with gently-inclined weak interlayer,taking the slope of Huangshan limestone mine in Sichuan as an example,based on the engineering geological analysis method,engineering geological analogy method,theoretical analysis and numerical simulation method,the geological causes of the soft interlayer and the instability mechanism of the slope are studied.The seepage characteristics of the mine slope with gently-inclined soft interlayer under different rainfall and continuous rainfall are revealed,and the stability of the mine slope under rainfall conditions is analyzed.The specific conclusions are as follows :(1)The sedimentation of the mining area occurred in the early Ordovician and Permian period.After a series of geological processes,a soft interlayer with large difference from the original soft rock was formed.Rainfall is the external factor inducing landslide instability,and soft interlayer is the internal factor controlling slope stability.Landslide is a failure mode composed of circular sliding and interlayer sliding,and the soft interlayer is the bottom sliding surface of landslide.(2)Soft interlayer is a impermeable layer,which will hinder the seepage channel of rainfall.With the increase of rainfall duration,the slope pore pressure growth rate and infiltration depth are gradually reduced.In the process of continuous rainfall seepage,the rainwater initially flows downward with the fracture network as the seepage channel.After infiltrating into the soft interlayer,the seepage path changes to flow to the slope foot along the upper surface of the weak interlayer.The fractured rock mass in the upper part of the slope is always in unsaturated state during rainfall.With the continuous rainfall,the upper surface of the soft interlayer and the position of the slope toe are first saturated,and the pore water pressure in the soft interlayer and the limestone has little change.(3)The overall stability coefficient of the slope decreases with the increase of rainfall duration and rainfall intensity,and the overall decline trend of the stability coefficient of the slope under cloudbrust conditions is the most obvious.The slope slides along the soft interlayer.The displacement of the slope changes little in the first six hours under the four conditions,and then the displacement will change abruptly.The slope is in danger under continuous rainfall or extreme rainfall weather conditions.The research results can provide important theoretical basis and research methods for the scientific and reasonable evaluation,prediction,optimization and treatment of mine slope stability under similar engineering geological conditions in southwestern China,and have certain scientific significance and practical application value.