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TBM (Full Face Tunnel Boring Machine) tunneling method has significant economic and technical advantages and is becoming an innovative method for deep roadway speedy construction. However, due to the special complex geological conditions and construction environment of coal mines, the technical challenges faced by TBM tunneling in deep roadways and the key scientific problems are analyzed: ① adaptive design of TBM equipment and the mine system under special tunneling environment in coal mine is difficult to fulfill; ② the rock fragmentation mechanism in soft and hard mixed strata is unclear, and the efficient rock cutting is difficult to realize; ③ The risk of soft rock squeezing deformation and TBM jamming, and the difficulty for accurate prediction and safety control is large; ④ Due to the narrow tunneling space and the serious interference of dust and water fog, it is difficult to monitor the tunneling process and make decision control and disaster warning according to the monitoring information. In this regard, systematic research on adaptive equipment design, efficient rock cutting in mixed-ground, squeezing deformation and TBM jamming disaster prediction and control method, and intelligent assisted tunneling method in deep composite stratum tunneling has been carried out. Research results on the TBM safe and efficient tunneling technology are achieved: ① the present situation of TBM adaptive design technology for special construction environment of coal mine is illustrated. ② full-size disc cutter penetration and linear cutting tests for hard and soft rock under high confining pressure are performed. Accordingly, the influence of complex geo-stress, rock strength and lithology change, tunneling control mode,cutter installation radius on the TBM cutting efficiency and rock fragmentation mechanism are revealed. The evaluation and prediction method of TBM tunneling performance and the corresponding rock mass classification method in deep mixed ground is put forward. ③ The mechanism of large deformation and TBM jamming disaster during TBM tunneling in deep coal measure soft strata is revealed. The FDEM (combined FEM and DEM) numerical simulation method of large deformation and TBM jamming disaster evolution and corresponding control measures for TBM tunneling in soft rock is developed. The monitoring and warning method of squeezing deformation and TBM jamming disaster is put forward. A comprehensive prevention and control technology system of ‘large diameter over excavation, excavation parameter optimization and step by step combined supporting’ is proposed for large squeezing deformation and TBM jamming hazard. ④ The real-time sensing technology of rock-TBM interaction information (cutter head - roadway face interaction, surrounding rock-shield interaction) in TBM tunneling process is proposed, and the adaptive intelligent decision-making method for advance parameters is initially developed. The research progresses will promote the application of TBM tunneling in coal mine roadway construction and safe and efficient tunneling technology.

Floor heave is a disaster that is frequently encountered in tunnel engineering. Existing explanations of floor heave mechanisms have many limitations, and the most important of which is that the stress concentration, release and transfer phenomena and the influences of the in-situ stress lateral coefficient and tensile strength are ignored. Therefore, the combined finite-discrete element method (FDEM) is used to study the failure process of floor rock masses and propose a new mechanical mechanism of floor heave that can consider the influences of the in-situ stress lateral coefficient and tensile strength. The type I fracture energy corresponding to different tensile strengths is calibrated using a direct tensile simulation test. Then, the floor heave mechanism is investigated under different lateral coefficients and tensile strengths, and five different floor heave modes are proposed under different in-situ stress lateral coefficients and tensile strengths. The floor heave modes controlled by the various in-situ stress lateral coefficients and tensile strengths are different, but they can all be explained by the maximum concentrated tangential stress. [ABSTRACT FROM AUTHOR]

To investigate the effects of the oval hole on the strength and the failure mechanisms of rock materials, a series of uniaxial and biaxial compression numerical simulations were carried out using the combined finite-discrete element method (FDEM). Based on the numerical simulation results, the effects of dip angle (β), major–minor ratio (ω) and position of the oval hole on rock strength characteristics crack initiation and development process and final failure modes were analysed in detail. The numerical simulation results indicate that: (1) Under uniaxial compression, the ultimate failure modes of rock containing oval holes can be mainly classified into single inclined plane shear failure, X-shaped tensile-shear composite failure and Y-shaped tensile-shear composite failure. Under biaxial compression, the ultimate failure mode is single-inclined plane shear failure dominated by shear cracks. Whether it is uniaxial compression or biaxial compression, the crack initiation position of the main fracture surface is near the end of the major axis of the oval hole. (2) Under uniaxial compression, the axial stress–strain curve of rock containing the oval hole is smooth before and after the peak, but under biaxial compression, there is obvious fluctuation in the post-peak stage due to crack initiation and propagation. In both uniaxial and biaxial compression, the pre-peak elastic stage of the axial stress–strain curve of the rock containing the oval hole is significantly shortened and the peak stress is significantly reduced compared with the intact rock, which indicates that the bearing capacity of the rock is seriously reduced by the existence of oval hole. (3) When the position and major–minor axis ratio of the oval hole remain unchanged, the uniaxial compressive strength and biaxial compressive strength increase with the increase of the dip angle of the oval hole. When the position and dip angle of the oval hole remain unchanged, the uniaxial compressive strength and biaxial compressive strength decrease with the increase of the major–minor axis ratio of the oval hole. (4) At different dip angles, the brittleness index Bi of rock containing oval holes decreases with the increase of confining pressure, and the brittleness degree shows a gradual weakening trend. At the same time, when the dip angle increases, the decreasing amplitude of brittleness index Bi decreases with the increase of confining pressure. Three types of failure modes of rock with elliptical hole are systematically summarised, and the failure mechanisms of elliptical hole rock are revealed. The influence of different positions, major–minor axis ratio, and dip angle of rock containing oval holes on uniaxial compression and biaxial compression are studied. The relationship between brittleness index and failure mode of rock containing the oval hole is investigated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The excavation in layered rocks is an issue for a number of geoengineering applications; these kinds of rocks all exhibit transverse isotropic features due to the process of metamorphic differentiation. This paper focuses on providing two methods, i.e., the 3D printing technology and the combined finite-discrete element method, to simulate the anisotropic characteristics of layered rocks. The results showed that both the 3D-printed samples and the FDEM numerical models are considered as a good match, and both revealed that as the inclined angle increased, the UCS of the sample first decreased and then increased, showing a U-shaped pattern. The results of this paper served as a reference to the promotion of the 3D printing technology and the combined finite-discrete element method in the geotechnical engineering field and laboratory test research. [ABSTRACT FROM AUTHOR]