RESUMO
Influenced by the anisotropy and water-softening characteristics of gently inclined layered shale, many tunnels have encountered bottom deformation issues during construction and operation, which severely impact the safety of tunnel structures. The energy evolution law during rock deformation and damage can provide support for the assessment and prediction of structure deformation. However, most studies have been conducted on enstatite, granite, and sandstone with limited research on shale. In this study, both conventional and single-cyclic loading-and-unloading uniaxial compression tests were conducted on shale specimens with varying dip angles of the structural plane (Dφ) and water content (Wc) in addressing the most typical layered shale in the Chaoyang Tunnel. The energy evolution features of rock samples at each stage of the tests were analyzed to determine the discriminating indicator (SC) for tunnel bottom deformation tendency. The indicator was based on the elastic strain energy (Uei) and the post-peak dissipation energy (Udi). The results demonstrated that the Dφ and Wc directly affected the energy storage and dissipation process of rock specimens, which in turn enabled them to exhibit different damage evolution features. The Uei and the total input energy (Uli) satisfied a linear relationship, which was determined by the Dφ and Wc of rock specimens. The energy evolution-based indicator SC can accurately characterize the bottom deformation of the tunnel constructed in a gently inclined layered shale stratum. The findings can offer a scientific foundation for rational evaluation of the structure deformation of tunnels under construction.
RESUMO
The gently tilt-layered shale displays anisotropic behavior and includes structural planes that cause the rock to exhibit weakened features. As a result, the load-bearing capacity and failure mechanisms of this type of rock differ significantly from those of other rock types. A series of uniaxial compression tests were performed on shale samples from the Chaoyang Tunnel to investigate damage evolution patterns and typical failure characteristics of gently tilt-layered shale. An acoustic emission testing system was incorporated to analyze the acoustic emission parameters of the shale samples during the loading process. The results indicate that the failure modes of the gently tilt-layered shale are significantly correlated with the structural plane angles and water content. The shale samples gradually transition from tension failure to tension-shear compound failure as the structural plane angles and water content increase, with an increasing level of damage. The maximum values of AE ringing counts and AE energy for shale samples with diverse structural plane angles and water content are reached near the peak stress and serve as precursors to rock failure. The primary factor influencing the failure modes of the rock samples is the structural plane angle. The precise correspondence between the structural plane angle, water content, crack propagation patterns, and failure modes of gently tilted layered shale can be captured by the distribution of the RA-AF values.
