Abstract: To elucidate the mechanism by which the bedding plane dip angle influences the stability of the surrounding rock in deep softhard interbedded water conveyance tunnels, and to develop targeted support schemes, the finitediscrete element method was used to calibrate the mesoscopic parameters of mudstone, sandstone, and the bedding planes. Numerical models with bedding dip angles ranging from 0° to 90° were constructed to systematically examine the influence of the bedding dip angle on deformation of the surrounding rock, stress evolution, and failure characteristics. Based on the results of numerical analysis, the onsite support scheme was optimized, and realtime monitoring was implemented. The findings are as follows: (1) In soft rock zones, tensile stress concentration and significant crack development occur at gentle dip angles (≤30°) and steep dip angles (≥75°), resulting in poor stability of the surrounding rock. In contrast, at moderate dip angles (45°－60°), the stress distribution in the surrounding rock is uniform, and the cooperative load-bearing capacity of the soft and hard rock layers is robust; the stability is optimal at a dip angle of 60°. The bedding dip angle modifies the load-bearing path and interlayer constraints, causing the tensile stress zone in the surrounding rock to exhibit a three-stage distribution characterized as “large-small-large”. (2) Under water conveyance conditions, the fracture seepage flow is characterized by an instantaneous peak, brief decline, secondary peak, and gradual attenuation; soft rock primarily governs the development of seepage channels, whereas hard rock serves as a water barrier. Based on the differential deformation characteristics of the surrounding rock, an asymmetric combined support scheme is proposed, which includes strong support for soft rock, simple support for hard rock, and key locking of the bedding planes. Engineering monitoring indicated that the maximum deformation of the surrounding rock reached approximately 48 mm. Convergence was observed after 40 days, and no leakage or spalling phenomena were detected in the tunnel section. The support control measures effectively meet the established requirements.

Key words: water conveyance tunnel, soft and hard interbedded rock mass, surrounding rock deformation, stress field, finite discrete element method, support design