Deformation process and mechanism analyses for a planar sliding in the Mayanpo massive bedding rock slope at the Xiangjiaba Hydropower Station

Planar sliding, which has a universal characteristic of existing planar discontinuities, is very common in nature. The Mayanpo slope, a massive bedding rockslide, typical planar sliding, exploiting a sedimentary formation of interbedded sandstone and argillaceous stratums mixed with four strongly weathered weak interlayers, presents creep deformation that has interrupted the construction of the Xiangjiaba Hydropower Station. Field investigations indicate that the deformation behavior of Mayanpo slope should be analyzed within two different zones, namely zone I (east side) and zone II (west side). Although both zones are primarily controlled by the bottom weak interlayer (JC-1), the deformation magnitudes and potential failure modes are different: (a) Zone I exhibits a deformation that is significantly larger in magnitude than zone II, and (b) zone I and zone II present multistage and integral creep-fracturing progressive deformation-failure mode, respectively. The mechanism of this creep deformation can be considered to be the endogenic and exogenic integration. The progressive degradation of predominant discontinuity from primary soft rock stratum to weak interlayer is the fundamental which provides the possibility of kinematic release. The numerical analysis conducted with hydromechanical finite difference method (FDM) shows that excavation without reinforcement and rainfall can (i) enable kinematic feasibility and creep deformation, (ii) trigger the ceaseless propagation of sliding zone along JC-1, and (iii) promote the formation of a tensile strain concentration zone in the trailing under tension-shear effect. Furthermore, discussions on the engineering core measures for prevention and control are presented, which have important implications for similar engineering projects.