To investigate the deformation and failure behavior of a tunnel excavated in mixed strata, transparent soft rock test and numerical simulations were performed. The distribution features of displacement and failure and the evolution laws were analyzed. In this study, a transparent material for simulating mixed strata was developed. The visualization of the spatial deformation inside rock masses will improve the understanding of this process. The tests suggest that the mechanical properties of transparent soft rock are similar to those of natural rock. Experiments on the isotropic and mixed strata conditions were carried out to study the deformation rules during tunnel boring machine (TBM) excavation. The test results show that the dominant deformation position and direction exist in isotropic and mixed strata. A shear slip band occurs in both mixed and isotropic strata but with different distributions. Finally, numerical simulations were conducted to study the failure process, and the damage pattern of the transparent soft rock experiment was similar to that of the numerical simulation. The interface of the softness and hardness layers controls the extension of rock damage.

For jointed rock mass with anisotropy and discontinuity, the structure of the surrounding rock is constantly developing and changing during tunnel excavation. It is difficult to reasonably predict localized deformation of jointed rock mass by using the existing rock mechanics theory. In this paper, the failure characteristic of pre-holed jointed rock mass with three joint angles is experimentally investigated by adopting the digital image correlation and acoustic emission methods. To avoid the influence of measurement error on Digital Image Correlation (DIC) from discontinuous deformation, parametric studies and an optimized algorithm are also included in DIC tests. Results indicate that the perpendicular-jointed condition (0° joints) is the most dangerous situation because of its comparatively lower strength and brittle failure mode with a shift energy release. For rocks with different jointed angles, localized deformation emerges after the material enters the plasticity. Significant localization occurs after the failure with cracks surrounding the center hole and pre-existing joints.

Fractured rock masses are extremely common in geological engineering. In order to improve the stability of surrounding rock under dynamic conditions, new grouting materials and their reinforcement characteristics were studied. In this paper, split Hopkinson pressure bar (SHPB) tests were employed to analyze the dynamic mechanical and failure characteristics of grouted fractured rock with nano-grouting material (nano-grouted fractured rock). Simultaneously, high-speed camera tests were utilized to examine the macroscopic dynamic deformation and failure processes. The following was found: (1) Under a relatively low impact air pressure of 0.1 MPa, the mechanical properties of nano-grouted fractured rock are considerably better than those of traditional cement-based grouted rock. However, when the impact air pressure is increased to 0.3 MPa, the superiority of nano-grouting material diminishes, the possible cause of which is explained from the microscopic point of view. This means the nano-grouting material is more suitable for low-engineering-disturbance conditions (e.g., shield construction). (2) Both for the nano- and superfine cement grouting material, the impact fractures initially emerge at the two ends of the original grouted fracture and form a pair of parallel lines. (3) In comparison with 0.1 MPa, the impact pressure of 0.3 MPa leads to more severe damage to the rock specimen. These findings contribute to a deeper understanding of the behavior of nano-grouted fractured rock under dynamic loading and provide valuable insights for relevant engineering applications in the field of rock mechanics and grouting technology.

As the development of deep underground engineering in modern days (i.e., exploitation of geo-energy and underground constructions), a higher demand arises for an accurate prediction of ground deformation and stability. For jointed rock mass with anisotropy, stress field and the structure of surrounding rock mass change with the underground construction, for example, during deep-ground tunnel excavation which is associated with ground depth and joint angles. Currently, it is difficult to reasonably predict localized deformation of jointed rock mass with existing theory. In this paper, characteristics of strength and failure mechanism of pre-holed jointed rock mass is experimentally investigated by adopting the digital image correlation and acoustic emission methods. The role of buried depth is considered with confining boundary applied during experiments. To precisely characterize deformation patterns and capture cracking via DIC, tests on DIC parameters and analysis algorithms are further carried out. Results show that joint inclination and confining condition exert a notable influence on the mechanical properties and failure behaviour of rock masses with centering holes. Rock mass exhibits ductile failure while applied with a confined boundary. The confining associated with buried depth in practical would pose an influence on the strength of the rock in particular for oblique jointed situations. The perpendicular-jointed condition poses the most significant risk in both shallow and deep buried conditions due to its relatively lower strength and the maintained brittle failure mode.