An experimental investigation on the anisotropic permeability of coal under cyclic loading and unloading conditions is presented in this article. The results show that coal permeability decreases with increasing hydrostatic stress. The relationship between coal permeability and applied stress was quantified using an improved power model. The cyclic loading and unloading were found to induce an irreversible permeability reduction, which tended to be diminished with increasing loading/unloading cycles. The anisotropic permeability of the studied coal is notable, and it was found to nonlinearly decrease with an increase of the angle between the direction of flow and the direction of bedding planes (θ). The relationship between permeability and θ can be quantified using an exponential model with an anisotropic parameter (λ). Several factors (e.g., loading cycles, stress) influencing the anisotropic permeability are discussed in this article.

Reducing seismicity during excavation is a challenge faced by mining and the associated slip development on a near‐excavation fault under deep‐mining stress conditions is considered as an analog for understanding earthquake initiation mechanisms. In this paper, the quasi‐static slipping on a dipping fault near a horizontal tunnel was numerically studied by incrementally increasing horizontal stress. The equilibrium of the fault, which obeys a slip‐weakening friction law, is formulated by a boundary integral approach. The calculated rupture size is a function of the dimensionless factors derived by scaling from geometrical, loading, and friction conditions. The results show that the rupture becomes runaway at a critical stress level and prior to this, the slip zone either extends continuously and aseismically or experiences finite rapid extensions. Energy dissipated in friction in the presence of tunnel‐induced stress heterogeneity can arrest fast rupture events resulting in regained equilibrium. The energy radiated from arrested events, using an energy budget analysis, depends on the resulting fault strength change, the rupture arrest length, and the strain energy change during the event. These preceding energy radiations can mitigate the magnitude of runaway events. As the critical slip‐weakening distance decreases, the critical stresses for nucleation of both runaway and arrested events are reduced, but the energy radiated by arrested events does not always decrease because the rupture arrest length varies. The results of this study may help identify the initiation mechanisms for runaway ruptures and assess the seismic potential of a rock mass during excavation.

The elastic compliance matrix is a key parameter for the stability analysis of engineering projects constructed in fractured rock masses. In this study, the energy equivalence and the superposition methods were used to estimate the elastic compliance matrix of rock masses containing persistent or nonpersistent fractures. For the energy equivalence method, two loading schemes were proposed to obtain the values of $S_{16}$ and $S_{26}$ for nonsymmetric fracture sets. The superposition method was proposed to estimate the compliance matrix of rock mass containing several fracture sets by summing the matrices of intact rock and each single fracture set. For a rock mass containing regular persistent fracture sets, the derived analytical results were consistent with closed-form results. The analytical results were also compared with the results of FEM for a rock mass containing two normally distributed nonpersistent fracture sets. The maximum deviations of the directional Young’s modulus, shear modulus, and Poisson’s ratio were 7.9, 11.3, and 21.3% respectively. The limitations of the proposed methods are discussed in this paper.

The investigation of concrete structural performance is crucial to maintain the stability of infrastructure. In order to assess structural stability, this work focuses on the development of an integrated framework to detect damaged conditions in the field and analyze their effect on mechanical performance through nondestructive testing (NDT) technology and numerical models. First, a ground penetrating radar (GPR) and an infrared camera work collaboratively to identify the damaged positions of the concrete structure, with parameters calibrated by laboratory experiments. Then, a finite element model is established to study structural mechanical performance based on field conditions and detected results. In addition, the influenced regions induced by local damage are studied under different boundary conditions. As a case study, the devised method was employed in the Nanjing Yangtze River tunnel for stability assessment and disaster prevention. The detected results of the damaged conditions agree well with the actual conditions in the field. Numerical results show that the circumferential stress component is more significant than that observed longitudinally. The effect of local damage on stress implies a positive correlation with the rise of water pressure, in which the maximum stress response to the variation of water level is 45KPa per meter.

Nano-polycrystalline vanadium oxide thin films have been successfully produced by pulsed laser deposition on Si(100) substrates using a pure vanadium target in an oxygen atmosphere. The vanadium oxide thin film is amorphous when deposited at relatively low substrate temperature (500 °C) and enhancing substrate temperature (600–800 °C) appears to be efficient in crystallizing VO _x thin films. Nano-polycrystalline V₃O₇ thin film has been achieved when deposited at oxygen pressure of 8 Pa and substrate temperature of 600 °C. Nano-polycrystalline VO₂ thin films with a preferred (011) orientation have been obtained when deposited at oxygen pressure of 0.8 Pa and substrate temperatures of 600–800 °C. The vanadium oxide thin films deposited at high oxygen pressure (8 Pa) reveal a mix-valence of V⁵⁺ and V⁴⁺, while the VO _x thin films deposited at low oxygen pressure (0.8 Pa) display a valence of V⁴⁺. The nano-polycrystalline vanadium oxide thin films prepared by pulsed laser deposition have smooth surface with high qualities of mean crystallite size ranging from 30 to 230 nm and R _a ranging from 1.5 to 22.2 nm. Relative low substrate temperature and oxygen pressure are benifit to aquire nano-polycrystalline VO _x thin films with small grain size and low surface roughness.