Anisotropic progressive fracture characteristics of surrounding rock in gently inclined layered tunnels

Abstract:

To study the Macro-anisotropic progressive rupture characteristics and damage modes of gently inclined layered surrounding rock influenced by structural planes, we analytically deduced the mechanical response mechanism of the layered rock′s structural instability. Using a coupled discrete-finite-difference analysis method and results from indoor triaxial compression tests on sand-mudstone, we developed a numerical mechanical model to characterize the macro-mechanical properties of the gently inclined layered surrounding rock. This model was then used to systematically investigate the mechanical behavior of the rock under varying structural plane inclination angles and spacings. The rupture characteristics and rupture evolution of gently dipping layered rock under different structural plane inclination angle and spacing are systematically studied. The results indicate that: 1)analytical analysis based on beam plate structure can better reflect the progressive fracture process of layered surrounding rock and distinguish its failure mode; 2)The established discrete element finite difference coupled numerical model can better characterize the anisotropic macroscopic mechanical properties of layered sand and mudstone under triaxial stress state; 3)The fracture of the matrix changes significantly with the change of the inclination angle of the structural plane, and the cracks mainly appear in the direction perpendicular to the structural plane, as the inclination angle of the structural plane increases, the matrix fracture will undergo secondary deflection, and the critical angle for sliding failure of the surrounding rock will be calculated α₁=24.43°, α₂=55.29°; 4)As the spacing between structural planes decreases, the fragmentation of surrounding rock increases and the total number of cracks increases. When the spacing between structural planes is less than 30 cm, the fragmentation of surrounding rock significantly increases. The research results can provide a certain theoretical basis and play a guiding role for the control of stability and optimal design of supporting structures for gently inclined layered tunnels.