Model test on stability of soft rock slopes composed of nearly horizontal redbeds with cracks

Regarding to the problem that soft rock slopes composed of nearly horizontal redbeds with cracks in the eastern Sichuan area is prone to sliding failure under long-term heavy rainfall conditions, based on a typical slope example with double weak interlayers, similar materials that can characterize the softening and cracking characteristics of the soft rock in water are prepared with elastic modulus and tensile strength as the main control factors. A laboratory physical test model on a soft rock slope with fissured nearly horizontal redbeds was constructed, and the deformation, crack propagation and stability evolution of the slope under long-term rainwater infiltration was investigated. The results show that (1) the development of slope deformation can be divided into three stages - initial deformation, uniform deformation and accelerated deformation failure; (2) the crack propagation of the slope mainly includes the ‘upper-narrow and lower-wide’ cracks developed from bottom to top in the rear of the slope, and the related cracks developed from top to bottom in the front of the slope. The crack propagation area is mainly concentrated between the upper and lower weak interlayers, where excess pore water pressure is easily gathered; (3) a numerical simulation of the test model via FLAC3D presents the seepage process of the thrust landslide, and shows that the excess pore pressure increases initially and then stabilizes gradually with time. At the weak interlayers and vertical cracks, the excess pore water pressure increases cumulatively; (4) the evolution process of the sliding surface and slope instability can be divided into three stages: shallow fracture development and penetration, fracture spreading to deep weak interlayers and gradual penetrating, fracture further extension and slope failure. The weakening of rock mass caused by long-term rainwater infiltration, together with the gradual development of cracks to the deep zone of the slope and their connections with the soft interlayers to form the multi-stage stepped sliding surface are fundamental reason of slope failure for the soft rock slopes composed of nearly horizontal redbeds with cracks.