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Spalling is a widespread dynamic disaster during blasting excavation in underground engineering. To clarify the coupled dynamic response and spalling behavior of an underground tunnel with a spray anchor, an investigation based on the rock–shotcrete combination was conducted using theoretical and numerical methods. The mathematical representation of stress wave propagation between rock and shotcrete was deduced based on the elastic stress wave theory. A novel method for predicting the location and time of initial spalling in a rock–shotcrete combination was proposed. A numerical simulation was conducted to verify the validity of the proposed theoretical method. In addition, the effect of the material's tensile strength, the loading amplitude, and the thickness of shotcrete on the stress evolution and spalling characteristics was studied. The results demonstrate that the initial spalling locations are sensitive to the relationship between the normalized tensile strength of the rock, shotcrete, and interface. A high incident amplitude can cause the initial spalling in rock, and the shotcrete or rock–shotcrete interface can cause initial spalling due to a low incident amplitude. The stress evolution and spalling characteristics are sensitive to the thickness of shotcrete. The location of the initial spalling failure changes with the thickness of the shotcrete. An appropriate increment in thickness and normalized strength of the shotcrete is beneficial to the dynamic stability of underground engineering. [ABSTRACT FROM AUTHOR]

When a blasting is executed near two tunnels, the blasting wave will trigger a dynamic response and damage to the tunnels. Depending on the tunnel distribution, the path of the blasting wave to the remote non-adjacent tunnels will change. The aim of this study is to analyze the effect of the tunnel distribution on the dynamic response characteristics of a remote non-adjacent tunnel. Numerical models of two tunnels were established by PFC2D and three different tunnel distributions were considered. The two tunnels were divided into the adjacent tunnel and the non-adjacent tunnel according to their relative distance to the blasting source. The dynamic stress evolution, damage characteristics and the evolution of strain energy of the non-adjacent tunnel were initially analyzed. The results show that the stress wave amplitude of the non-adjacent tunnel is closely related to the tunnel distribution, but only near the sidewalls of the non-adjacent tunnel is the stress wave waveform sensitive to the tunnel distribution. The larger the tunnel dip, the more severe the damage to the non-adjacent tunnel. In addition, as the tunnel dip increases, the maximum strain energy densities (SEDs) in the roof, floor and sidewalls of the non-adjacent tunnel exhibit different trends. The influence of the wavelength of the blasting wave is further discussed. It is shown that the dynamic stress amplification factor and damage degree around the non-adjacent tunnel is usually positively correlated with the wavelength of the blasting wave. Moreover, the release of strain energy around the non-adjacent tunnel has a positive correlation with the wavelength. The SED variations in different areas around the non-adjacent tunnel also exhibit different trends with the increase of tunnel dip. [ABSTRACT FROM AUTHOR]

Numerical models of a deep and inverted-U-shaped roadway were established by a particle flow code (PFC2D), and four numerical tests were performed with different blasting locations. The dynamic response characteristics of the deep roadway under blasting disturbance were thoroughly analyzed. According to the failure patterns resulting from the simulations, the dynamic stability of the arch was stronger than that of the vertical wall. The effect of the blasting location on the blasting vibration was assessed, and the diffraction start region and diffraction end region of the stress wave were obtained. The radial stress wave and tangential stress wave around the deep roadway were obtained during the blasting. The results show that the diffraction start region and diffraction end region of the stress wave were related to the fluctuation of stress wave. The effect of depth on the dynamic stability of roadways were analyzed. The results show that the damage around the borehole will be inhibited in the deeper stratum, and the vicinity of the roadway are more prone to break in the deeper stratum. • The dynamic stability of the arch was stronger than that of the vertical wall. • The blasting vibration characteristics of surrounding rock are closely related to the blasting position. • The diffraction start region and diffraction end region of the stress wave are related to the fluctuation of stress wave. • High in-situ stress can weaken the dynamic stability of roadway but inhibit the damage of surrounding rock of a borehole. [ABSTRACT FROM AUTHOR]