This study focuses on typical anisotropic layered rock masses in deep engineering, specifically targeting rock layers with a dip direction of 90°. By employing various loading paths coordinated with stress level and Lode angle, the strength evolution on the deviatoric stress plane and the failure mechanisms of rock masses with different bedding dip angles were systematically investigated. The main findings are as follows: (1) For two rock masses with complementary bedding dip angles, their strength envelopes on the deviatoric stress plane are symmetrically distributed about the strike direction (Y-axis). When the dip angle is 45°, the envelope itself is also symmetric about the Y-axis. (2) When the Lode angle is 90°, the failure of the rock mass is entirely controlled by the rock matrix, independent of the bedding dip angle. (3) The dominant mechanism of rock mass failure varies with the Lode angle: for rock masses with dip angles of 45° and 75°, matrix-controlled failure occurs within Lode angle ranges of 240°–300° and 90°–310°, respectively. For a dip angle of 60°, the corresponding ranges are 90°–100° and 220°–310°. Under other Lode angle conditions, failure is jointly controlled by the matrix and the bedding planes. The results of this study provide theoretical guidance for a deeper understanding of the mechanical behavior and failure mechanisms of layered surrounding rock under complex stress states, and offer valuable insights for rapid stability assessment and support design in related engineering projects.