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Studying the mechanical properties of rock mass plays a critical role in reducing the frequency of accidents such as large deformation and rock bursts that often occur in tunnels. In this study, a series of phyllites with different bedding structures and mineral compositions were drilled from different tunnels firstly, then the effects of different bedding angles and mineral compositions on the mechanical properties and failure modes of phyllites under unloading confining pressure conditions were studied. The results show that the deformation characteristics of phyllite have complex relations with confining pressure, bedding angle and mineral composition, and the influence of other parameters cannot be ignored to quantitatively analyze the influence of a certain parameter. The strength of phyllite shows an increases trend as the increase of confining pressure, while the strength shows a trend of first decreases and then increases as the increase of bedding angle. Under the same confining pressure and bedding angle, the strength of phyllite with more quartz is generally the largest, followed by phyllite with more chlorite. With the constant release of confining pressure (unloading), the elastic modulus of phyllite decreases and the Poisson's ratio increases, and the rate of decrease and increase varies with the tunnel bedding angle and mineral composition. The bedding angle, mineral composition and confining pressure have great influence on the unloading failure mode of phyllite, but the influence degree is different. The bedding angle has the greatest influence on the failure mode of phyllite, followed by the mineral composition, and finally the mechanical environment.

The reasons why large deformations of inclined and laminar stratum occur in complicated geological conditions during tunnelling remain unclear. In this study, the geological conditions, the initial design of excavation and support and specific deformation failure modes of the laminar stratum and initial support system were first introduced at the Yangjiaping tunnel in China. Thereafter, field surveys, laboratory tests and numerical simulation were performed to investigate this complicated deformation and mechanical behaviour. Meanwhile, by combining buckling and catastrophe theory, the occurrence criteria of the deformation and failure of such stratum were established. Finally, excavation and support adjustments were proposed to control the rock mass deformation. The theoretical criterion reveals that buckling failure of the laminar structure has an obvious influence on the large deformation occurrence. By adopting the adjusted excavation and support measures, the rock mass deformation and contact pressure between the surrounding rock mass and initial lining are both dramatically decreased. The largest decline in the average horizontal convergence is approximately 25 cm; the maximum contact pressure value is approximately 1.149 MPa at the right haunch, which is about 64% of the value at the same location when using the original excavation and support method.

Tunnel construc tion is a common phenomenon in the complex geological environment, especially in soft rock, whose rock rheological characteristics cannot be ignored, so it is necessary to develop a new support method for soft rock tunnel. In this paper, based on the traditional convergence constraint method, the time factor is taken into account, and the characteristic surface method of surrounding rock considering the rheological characteristics is analyzed, and then, a multi-layer support method is proposed according to the Maoxian tunnel. This method can bear the rheological pressure of long-term stability of squeezing soft rock tunnel with large deformation. The results show that the soft rock tunnel has obvious rheological properties, and the rheological pressure increases with time. Considering the rheological characteristics of soft rock, the deformation, supporting force, and time of the soft rock tunnel was described by a specific continuous curved surface. The results of the characteristic curve method of soft rock tunnel show that the deformation of surrounding rock release has an obvious improvement effect on the supporting structure force, but the improvement effect is gradually weakened. The multi-layer support system from weak to strong, soft first, and then rigid can not only realize the reasonable release of surrounding rock displacement, but also ensure structural safety.