Study On Deformation Behaviour And Control Technology Of Weak Rock Surrounding Tunnel

The problem of stability and deformation control for weak rock tunnel is one of the focus in the tunnel field. During the constructing, the design concept, the stability analysis method and deformation control technology are usually becoming control factors, which affect the safety of tunnel construction, construction cost and construction period in finally. In the past years, by the means of collaboration, many hard works had been done, and a considerable progress has been made in some areas, but it is still far away from forming a mature theory system in soft weak surrounding rock tunnel. In this paper, based on the domestic and foreign existing research results, and considering of the actual situation of the partial excavation during the constructing of railway tunnel in China, a systematic research was carried out, including of the deformation characteristics, stability identification and deformation control technology during excavation of soft weak surrounding tunnel. By the means of numerical simulation and field test in typical engineering, the following results were put forword:(1)The tunnelling deformation consists of the prior deformation before excavation, the deformation of woring face and the later deformation after excavation. The range of prior deformation before excavation is within1.5D ahead working face. For the prior deformation of weak rock tunnel, the crown settlement more obvious than horizontal convergence.(2)For the soft weak surrounding rock tunnels, the displacements such as the squeezing deformation of working face and the arch springing settlement afer excavation are obvious. After the excavation, the main directional displacement is horizontal convergence for single track railway tunnel, and crown settlement for double-track tunnel.(3)The essential reason of large deformation in weak rock tunnel is the weak of surrounding rock and high of in-situ stress value, the plastic zone distribute range and depth of surrounding rock around the tunnel is relatively large during construction process, and the main directional displacement is along with the main development orientation of plastic zone in generally.(4)The limit state of tunnel system was defined. The tunnel stability of soft weak surrounding rock was defined that the surrounding rock during the construction does not collapse, the tunnel displacement harmonious develops and converges, supporting structure does not appear the cracking and breakage of affecting the bearing capacity. When the surrounding rock and supporting system get together, or part of it be to the limit state above, the state is looked as the stability limit state of the tunnel.(5)Introduced the catastrophe theory into the tunnel engineering, and an analysis method of surrounding rock stability was put forword, basing on catastrophe theory by plastic strain. At the same time, the corresponding limit displacement is obtained.(6)Based on the different material properties and support effects of the spray concrete and steel frame, two different action time were considered. Acorrding to the definition of the limit state of supporting structure, the corresponding limit displacement of supported tunnel for different surrounding rocks, different buried depth is obtained.(7)A nonlinear buckling model was applied to analyze limit load and unstable mode of supporting structure. The result shows that the limit load of supporting structure are within1.0MPa, when the reaction coefficient of bolts are between20-100MPa/m. It reveals that in the condition of high ground stress, it is likely that the supporting structure take place the whole crushing damage. At the same time, when the supporting structure is in instability, its deformation is discordant development. This is mached with actual project.(8)Combined with numerical analysis and field test results, the deformation control technology system of soft weak surrounding rock tunnel was proposed, which Including excavation control techninology, supporting control techninology, control techninology of working face and arch springing stability, supporting reinforcement technology, advance support technology and space deformation monitoring and feedback technology, and so on.(9)According to the statistical results of numerical analysis and field test, the calculating ultimate displacement, the limit load of supporting structure during the construction process, as well as referencing the successful experience of related projects, the deformation-control standard for was proposed.(10)Based on the all research results above, and drawing lessons from related engineering experience of domestic and foreign, different deformation controlled measures of soft weak surounding rock tunnel was proposed, for different conditions. And the research results are applied in the related projects and the operation performance were excellent.