Abstract: In recent years, numerous giant landslides have been identified in the tectonic suture zones of the Qinghai–Tibet Plateau, and their occurrence has been shown to be closely associated with clay-altered rock masses. Using the Baige Landslide in the Jinsha River tectonic suture zone as the study background, this study focuses on rock masses containing altered clay interlayers. On the basis of fully considering key factors such as rock wall strength, structural plane undulation, clay filling degree and water content, a series of cyclic shear tests was conducted on the structural planes. Using methods such as 3D laser scanning, scanning electron microscopy (SEM), and two-dimensional particle flow grogram PFC2D, the mechanisms by which altered clay interlayers affect the strength of rock mass structural planes under different conditions were comprehensively investigated. The results indicate the following: 1) Shear deformation and failure of the structural plane containing the altered clay interlayer proceed through four stages: compaction and slip, crack initiation and propagation, mixed wear of the altered clay and the asperity surface, and final shear penetration of the structural plane. 2) The principal factors controlling the behavior of the structural plane containing the altered clay interlayer are the filling degree and water content of the altered clay, followed by rock wall strength and structural plane roughness. 3) As the filling degree of the altered clay increases, the peak strength of the structural plane decreases rapidly at first and then gradually stabilizes, while the mechanical behavior becomes increasingly dominated by the clay interlayer; the maximum reduction reaches 82.6%. 4) Based on the experimental data and numerical simulation results, a formula for estimating the shear strength of structural planes containing altered clay interlayers is proposed. These findings provide a theoretical basis for determining design parameters for similar landslide mitigation projects.

Key words: altered clay interlayer, rock mass structure, structural plane shear strength, mechanical behavior, penetration mechanism