Instability Process Model Test for Bedding Rock Slope with Weak Interlayer under Different Rainfall Conditions

The instability process of bedding rock slope with weak interlayer may be induced under rainfall infiltration conditions. Due to this, we conducted a research of model test for the instability process, based on the similarity theory. With use of the recent 50 years' rainfall data of Changsha, China, we analyzed the seepage characteristics, mechanical characteristics, and deformation laws of the slope under the conditions of long-time heavy rain and short-time rainstorm, respectively. The test results show that the original seepage characteristics of the slope were changed by the existence of weak interlayer, presented the "double seepage" effect, resulted in the seepage characteristics of rock and soil in the shallow layer and weak interlayer of the slope showed a sickle "I" distribution, and the adjacent rock layer presented a curve-type "S" distribution. With the increase of rainfall duration, the weak interlayer gradually became muddy and softened, and then the plastic flow zone was formed locally. The stress concentration phenomenon was gradually generated in the weak interlayer due to the influence of the gravitational field of the upper rock mass. The large infiltration of rainwater led to the phenomenon of plastic flow extrusion of the slope at the weak interlayer extrusion. With the further penetration of the tensile cracks in the upper part of the weak interlayer, the slope had a large settlement displacement and gradually formed sliding shear deformation along the weak structural plane. Under the condition of equal rainfall amount, the condition of long-time heavy rain has a greater influence on the stability of the bedding rock slope with weak interlayer than that of short-time rainstorm. The failure form of slope could be divided into four stages: prechange stage, interlayer extrusion stage, slip-pull-fracture stage and plastic flow-shear failure stage.