Under the influence of plate collision, the high geothermal is a widespread phenomenon within the region of Tibet. Due to the aforementioned high geothermal, lining cracking is a common disaster in Sangzhuling tunnel during construction period. This paper presented the mechanical behaviour of tunnel lining under high geothermal temperature, which is studied by thermo-mechanical numerical method. The results both from field investigation and numerical analysis demonstrate that high geothermal temperature can cause the tunnel lining cracking and the variation of the stress of the tunnel lining. Thus, a novelty sandwich composite lining supporting scheme is proposed to overcome such geothermal temperature effects, in which a thermal insulation layer between primary supporting and secondary supporting is designed. The numerical analysis results indicate that the insulation layer can significantly improve the mechanical characteristics of the lining structure. In addition, the effect of the insulation layer is not linear with its thickness. For this reason, the optimum insulation thickness of the insulation layer is chosen as 0.06 m, which was optimized by a numerical parametric analysis. The research can provide a reliable reference for tunnelling works in high geothermal regions.

The dynamic compression properties of transversely isotropic rocks and their dependence on the confining pressure and bedding directivity are important in deep underground engineering activities. In this study, a slate is characterized using a split Hopkinson pressure bar (SHPB) test. Five groups of samples with preferred bedding directions (dip angles of 0°, 30°, 45°, 60°, and 90°) are subjected to coupled axial impact loading (low, medium, and high) under confining pressure (0, 5, and 10 MPa). The failure mode, dynamic strength, and Young’s modulus are investigated. The test results show that the tensile splitting effect is significant when there is no confining pressure. However, under a confining pressure (5 and 10 MPa) condition, the cracks that develop along the loading direction can be significantly constrained and the samples are forced to fail along the bedding plane. With increasing confining pressure, the critical dynamic strength significantly increases, and Young’s modulus increases when θ ≥ 45^° while it decreases when θ ≤ 30^°.

The drilling and blasting method is widely used in tunnel engineering. The accompanying airblast may damage structures and annoy nearby occupants. The prediction of airblast overpressure (p_oa) outside the tunnel is necessary to improve the safety of blasting works. A study of propagation characteristics of airblasts induced by tunnel blasting was carried out through experimental and numerical studies. The results indicate that the distributions of the p_oa outside the tunnel were anisotropic, which does not conform to the decay law of an explosion in free-field. The propagation of airblasts induced by tunnel blasting is related to the airblast shape. The phenomenon that the p_oa along the axial direction of the tunnel was higher than along other directions can be explained by the numerical results of the process of airblasts. The airblasts outside the tunnel traveled as a spherical wave, but the pressure was not uniformly distributed. After an airblast plane wave with high speed and high pressure inside the tunnel was transmitted out of the tunnel, its inertia strengthened the pressure in the axial direction. The airblast outside the tunnel is related to the propagation distance R_out, the angle from the measurement to the tunnel axis α, and the pressure intensity p₀ at the tunnel portal. Subsequently, an ellipsoidal contour curve of the p_oa outside the tunnel was plotted, and therefore a new prediction equation was validated by numerical results and field data. Finally, the newly proposed methodology guided the blast design.

A layered rock usually exhibits strong anisotropy due to its layered structure. In order to study the anisotropic effect on its static and dynamic tensile properties, a medium strength anisotropy slate is chosen and tested in five groups of bedding plane dip angles. The dynamic tests were carried out by a split Hopkinson pressure bar (SHPB), and the failure process of rock samples is recorded by a high‐speed camera. The failure mode and strength characteristic of the slate are analyzed. The static test results show that layered structure significantly affects the failure mode, and the influence of the bedding plane depends on the degree of anisotropy. The static and dynamic “tensile strength” exhibit the “U” type strength anisotropy. For samples in the same dip angle group, the “tensile strength” shows clear dynamic strengthening effect, and the growth rate is most significant at θ = 45°.