The Study On Rupture Angles And Failure Modes Of Circular Shallow-buried Tunnels

In recent years, with the rapid development of China’s economy, and the acceleration of urbanization, our state’s investment in subway construction and other aspects of transport infrastructure continues to increase. There have been a lot of shallow tunnel projects, so the basic theoretical study of shallow tunnels gets more and more attentions. Currently research of tunnel surrounding rock stability is mainly focused on the depth ones. Because of the poor rock conditions and small overburden depth, shallow tunnels are difficult to form stable arch. So in the field of shallow tunnels, the rock stability and pressure analysis of deep tunnels can’t be directly applied. The study of shallow tunnels needs to be further improved. Therefore, in this article, numerical simulation method based on strain-softening model has been sued to analyses the destruction of shallow tunnels. The main contents are as follows:(1) By changing the depth of the tunnels or the surrounding rock parameters, we can get different rupture angles, and analyze the impact of various factors on them.(2) By analyzing ground deformations and crack propagations, it is possible to explore the destruction forms of shallow tunnel surrounding rocks. In addition, the effects of different tunnel depths and soil strength on the surrounding rock failure modes also can be determined.(3) Different ways of calculating rupture angles are going to be compared for studying the differences between different calculation methods and merits of cases.(4) Using curve fitting to study the geometry of the tunnel slipping surfaces; and by curve fitting analysis, we can study the influence of various factors on the slumping body areas, also summarize the relevant laws.The main conclusions are as follows:(1) The facts such as depth, elastic modulus, friction angle and cohesion, have a significant impact on rupture angles. The relevant law is that:the rupture angle decreases as the depth increases, and it increases when elastic modulus, friction angle, and cohesion increases.(2) In the shallow-buried tunnels, the larger tunnel buried depth or weaker surrounding rock is, the larger the scope of damage will be, and the number of the failure surfaces is also big. There are going to be many cross-shaped internal shear failure surfaces in the collapse bodies. Meanwhile the worse the soil condition is, the more intense the destruction process will be, and the ground subsidence is also going to be larger.(3) With the improvement of the surrounding rock strength, slumping body volume will become small. Ellipse’s longer axis and the minor one have linear correlation with the tunnel depth; the relationship between the area of the collapse ellipse and tunnel depth is close to a quadratic curve.(4) For the tunnels of greater depth, from the beginning to the end of the destruction, this process has more than a temporary stabilization phases. It is a gradual process from one stabilization phase to another. The entire expansion process of destruction is gradual and phased.