Research On The Stability Of Surrounding Rock In Theconstruction Of The Tunnel With Large Span And Small Spacing

With the rapid development of urban construction, the construction of the subway is developing rapidly. For a variety of reasons, the tunnel in the middle and lower reaches of the development is increasing, and the distance between them is getting smaller and smaller. In recent years, in order to solve this problem, a new type of tunnel structure has been proposed by tunnel engineers, that is small spacing tunnel. This new form of tunnel can be overall alignment and terrain conditions, is a kind of traditional separated tunnel and double arch tunnel between the new tunnel structure, to a certain extent make up for the traditional separated tunnel and double arch tunnel is insufficient, compared with the double arch tunnel with the advantages of flexibility and applicability as well as the construction process is relatively simple, easy to handle, easy to control the cost of waterproof etc.. But for different rock types of the small spacing tunnel especially soft rock tunnel, its engineering property is relatively poor, but due to the process of the tunnel itself more construction, the construction of surrounding rock by disturbance effect is more obvious, the stability of surrounding rock by tunnel effect will be more direct; when the tunnel between the spacing is small to a certain extent especially when the soft rock tunnel, the plastic zone will be the superposition of serious, the stability of surrounding rock will be reduced obviously at this time, the economy of the tunnel construction safety and relevant supporting project will be greatly reduced.Therefore, it is of great significance to study the influence of the construction process on the stability of surrounding rock of large span and small spacing tunnel, and to determine the most economical and reasonable construction scheme.In this paper, the method of combining theoretical analysis and numerical calculation is used to study the different construction methods of large span and small spacing tunnels. The main research results are as follows:(1) Founding in the stress analysis of tunnel lining structure of three different construction methods: the axial force of lining structure by the maximum value in the tunnel near the middle rock section of the arch waist, and its value range is basically the same; the maximum bending moment of tunnel lining under value basically at the arch foot chamber.(2) Through the study of comparative analysis of three kinds of the surrounding rock deformation index under different construction method after the discovery, the tunnel construction in the use of bench method, the measured tunnel settlement value index than the other two methods under the index, at the same time the double side drift method CRD method compared with surrounding rock in the construction of the tunnel surrounding disturbance is slightly decreased. The selection of temporary lining structure in the use of CRD method and the method of double side when the tunnel sections were split, the excavation and the excavation section are very small, temporary lining and construction in the application of the method in a certain extent control the hole diameter within the range of displacement of surrounding rock, which is reduced a very effective method for the deformation of surrounding rock.(3) Using three kinds of different construction methods under construction when the surrounding rock exists in the stress concentration phenomenon is very serious, and the stress distribution is roughly the same as in the basic pilot tunnel excavation steps each corners and sharp corners. When the tunnel construction is completed, the stress is mainly concentrated in the vault, arch foot and invert. Large section and small spacing tunnel in rock is the weak part of the tunnel excavation process, through different construction methods for the investigation of the stress results showed that the selection step method for the construction of stress value with CRD selection method and the chosen method of double side construction data is larger than 44%, compared with under the stability of rock is more bad; but at the same time as the CRD method and the method of double side excavation in construction process are very complex, stress concentration phenomenon is very obvious, the stress is mainly concentrated in the temporary support structure and initial support joint support structure, but compared to the tunnel surrounding rock influenced by the stress concentration of the contrast is the lightest. For the whole working condition, the maximum and minimum principal stress of most of the surrounding rock are in the state of compressive stress under three different construction methods.(4) To observe the three kinds of construction methods of surrounding rock deformation and stress can be found, the location is very prone to cracking and falling even overall collapse; so you can see for rock tunnel in strengthening the overall stability of the tunnel surrounding rock, we in the field of construction process through the first whole rock grouting can improve the wear type and then the reinforcement of prestressed anchor rock used in dyke,so as to ensure the stability of rock tunnel in the clip.