Research On Suitability Of Supporting Types For Large Deformation Underground Chamber In Squeezing Ground

With the rapid development of transportation infrastructure construction,numerous tunnels through high stress domain and soft rock have been built in recent years, inducing more and more large deformation disasters. Bolt abruption, steel support distorted, shotcrete cracking and other large deformation disasters appeared in varying degrees in lots of soft rock tunnels under-construction or already built, even leading to collapse. Up to now, various types of supports were proposed for large deformation of soft rock tunnels, yet there is no unity because of the disadvantages and lack of universality. Therefore, it is necessary to research the suitability of the supporting types for large deformation underground chamber in squeezing ground.Based on the diversion tunnel project in Jinping Ⅱ Hydropower Station, investigation, theoretical analysis and numerical simulation were comprehensively used to research the suitability of different supporting types for large deformation underground chamber in squeezing ground. The main research results are as follows:1.At present, three kinds of supporting types are commonly used in large deformation underground chamber in squeezing ground, namely strong supporting, layered supporting and yielding supporting. However, the strong supporting with reinforced supporting resistance, high stiffness and cost is the mainstream type in tunnels of this kind.2.Analysing the mechanism of three kinds of commonly used supporting types, results show that it is unrealistic to rely on strong supporting to solve the problem of large deformation. And the applicability of layered supporting is weak in both theory and practice. Meanwhile, the yielding supporting system need solve the problem of yield amount,yield point, constant resistance and coordinate deformation.3. Based on the analysis of the calculation results, the influence law of supporting strength on the stability of surrounding rock under different squeeze factors is obtained, as well as the applicability of each supporting types. The result shows that:yielding supporting should be used for the severely squeezed surrounding rock (Nc<0.15); well it is suitable to use strong supporting for lightly squeezed surrounding rock (Nc≥0.15).Combined with relied project, comparative analysis of the advantages and disadvantages of each supporting types was carried out, the result shows that yielding supporting is the best choice for large deformation underground chamber in severely squeezing ground because of both the timely strong support and function of flexible supporting.