Abstract: In this study, the force behavior of single-layer lined drainage tunnels under complex loads in nuclear power projects is finely and efficiently simulated, and their influencing elements are analyzed. Additionally, a cross-scale fine model of tunnel-foundation is established based on the octree discretization technique, and a coupled finite element-scaled boundary finite element analytical algorithm is employed to systematically examine the influence of four types of elements—the type of stratum, the inner diameter of the tunnel, the depth of the tunnel, and the pressure of the internal water—on the single-layer lining stress pattern based on 24 working conditions. Finally, the correlation and potential mathematical relationships among these factors are analyzed. The results demonstrate the following: (1) The proposed approach effectively improves the efficiency of stress analysis of tunnel structure (34.3% for representative case), being beneficial to analysis efficiency of multi-case simulation such as sensitivity and susceptibility. (2) The influence of various factors on the stress of single-layer lining is quantified, and the influencing order is determined. The tunnel burial depth has a greater influence on compressive stress, while strata type and internal water pressure have a greater influence on tensile stress. (3) The potential mathematical relationships between the inner diameter of the tunnel and the maximum internal water pressure and that between the maximum burial depth and the maximum internal water pressure are clarified using polynomial fitting. 

Key words: octree discretization technique, cross-scale fine modeling, finite element method-scaled boundary finite element method, single-layer pressurized tunnel, nuclear power structure