A moment tensor analysis of acoustic emission was applied to quantitatively study the microcracking mechanism and damage evolution process in cylindrical specimens of granite and sandstone under diametral compression. It was found that the localized damage zone tended to originate and propagate from the vicinity of the loading ends. During the damage accumulation process, the tensile cracks played a dominant role in number, but the acoustic emission (AE) energy release of microcracks of different types presented an inconsistent trend for the two types of rock. Scanning electron microscope (SEM) observations on the fractured surfaces were conducted, which indicated that during the rock failure process there coexisted microcracks of three types—tensile, shear, and mixed-mode—due to the heterogeneity of the mechanical properties of the rock. The microscopic observations using a polarized light microscope technique revealed that the mineralogical composition and microstructure of rock had a significant effect on its microcracking mechanism.

For better understanding of rock fragmentation mechanism and correlative influence factors under the cutter penetration, a set of two-dimensional wedg

Rock has the characteristics of natural heterogeneity and discontinuity. Its failure phenomenon induced by external force involves complex processes, including the microcrack initiation, propagation, coalescence, and the macrocrack formation. In this study, the Weibull random distribution based on the rock microstructure characteristics is introduced into the combined finite-discrete element method (FDEM) to establish the heterogeneous rock model, and the mechanical response and damage evolution of rock samples in uniaxial compression test are simulated. The results show that FDEM simulation with loaded heterogeneous rock model can reflect the progressive development of rock damage, fracture, and acoustic emission (AE) activity in real rock well. Meanwhile, the statistical analysis indicates that the number and energy evolution of AE events with different fracture modes in the model are consistent with the macroscopic failure mode of rock. The change of b-value also agrees with the increasing trend of high-energy events in the loading process. This method provides a new tool for the analysis of rock damage and fracture evolution.

To better understand the rock fragmentation mechanism and optimize cutter design and selection for rock excavation by TBM, a set of three‐dimensional indentation tests was conducted with different rock and cutter types. Acoustic emission (AE) monitoring technique was employed to capture the information of the rock damage evolution real‐timely. It is found that the penetration by using the constant cross section (CCS) cutter tends to induce inconspicuous rock chips formation before the sudden occurrence of the macrocrack, but that by using the V‐type cutter tends to induce gradual rock fragmentation accompanied by the multiple local rock chips formation and the sawtooth force‐penetration curve. Meanwhile, rock fragmentation models for CCS and V‐type cutters were compared, and the spatio‐temporal evolution of AE events was quantitatively analyzed to reflect the rock damage zone development process. Results indicate that the V‐type cutter has greater penetration ability and the CCS cutter can cause larger unit damage zone radius. Microscopic observation by using the scanning electron microscope (SEM) reveals that the fracture mechanism for the crushed zone of rock is mainly shear type and that for the major crack is tensile type. It does not matter with rock types or cutter types.

In order to study the mechanical deformation response law and stability difference of surrounding rock induced by the unloading effects of tunnel excavation with different section types, the 3D numerical tunnelling simulation was conducted. The results show that the plastic zone depth and deformation value of the surrounding rock of the circular tunnel are the smallest, and its stress distribution is uniform. The plastic zone depth and volume of the surrounding rock of the horseshoe-section tunnel are slightly larger, the rock deformation is about 10% larger than that of the former, and its stress distribution is relatively uniform. However, the plastic zone depth of the surrounding rock of the gate-section tunnel is 0.7-1.2m larger than that of the circular tunnel, and plastic zone volume increases by about 28.5%. Meanwhile, the surrounding rock deformations at the sidewall and floor of the gate-section tunnel are larger, and its deformation gradient is higher. The stress concentration phenomenon at the intersection of the floor and the sidewall is also significant. Therefore, the surrounding rock stability of gate-section tunnel is considered to be most unfavourable among the three tunnel section types. In consideration of tunnel stability, construction difficulty and economy, the horseshoe section type is recommended.

To explore the suitability of the supporting scheme of horseshoe tunnel affected by different buried depths in phyllite rock, the 3D numerical tunnelling simulations were conducted. The plastic zone distribution, deformation characteristics and stress field of surrounding rock and mechanical characteristics of supporting structures during the excavation process were analyzed. It was shown that the plastic zone depth, volume and deformation development of the surrounding rock are greatly limited by the shotcrete-bolt support under different buried depths. Meanwhile, the restriction proportion to the development of the plastic zone and rock deformation is slightly affected by the buried depth of the tunnel. With the increase of the buried depth of the tunnel, the reasonable shortest distance that should be reserved between the constructed lining and tunnel face also gradually increases. Combined with the calculated tunnel deformation and the classification standard proposed by Hoek, it is recommended to adopt full-section shotcrete-bolt support, and add steel arch support as the necessary supplement for the existing tunnel supporting scheme. The research results contribute to design and construction guidance for tunnels under similar geological environments.