Study On Approximate Building Method Of Ground Reaction Curve For Non-circular Underground Caverns

As the population increasing, the rapid development of national economy and national defense construction, the development and utilization of underground space are unfolding, the underground caverns, tunnels and roadway of various shapes and sizes are excavated in the strata. And after the underground excavation, the elastic-plastic stress and displacement distribution around the surrounding rock has an important impact on the designation and construction of supportting structure, which is also important for surrounding rock stability analysis. Therefore, the research of elastic-plastic Ground Response Curve of surrounding rock that used to characterize the relationship between post-rock stress and displacement of underground excavation has become an important part of the stability analysis of underground caverns.Limited to the current development level of elastic-plastic mechanics, only circular cavern possesses integral analytical form of Ground Response Curve currently, the non-circular cavern need to fit through complex numerical methods. To improve the computational efficiency of non-circular cavern and to expand the scope of analytical method, and in favor of the application of convergence-constraint method in non-circular underground tunnel support designation, the equivalent circular method was discussed when building approximate analytical GRC for non-circular cavern in this article.First of all, the set-up process for the Ground Response Curve of Karstner that do not consider plastic-expansion and the Ground Response Curve of Duncan-Fama that consider plastic expansion are deduced respectively, and detailed analysis and summary are made for existing equivalent circular method. Secondly, taking the arch wall cavities for example, using numerical method to obtain the elastic-plastic stress and displacement of the surrounding rock of the non-circular cavern after excavation, and the corresponding Ground Response Curve is drew. And, a contrast analysis was made between the above numerical GRC curve and the approximate analytical GRC curve under the same initial conditions that based on various equivalent circular methods, which can reveal the applicability of different equivalent circular methods.Then, according to the research method of straight wall arch cavity to analyze the most appropriate equivalent circular method when solving approximate GroundResponse Curve for rectangular cavity and curved wall arch cavity, and then,exploring the influence of span-depth ratio, surrounding rock level,the cavity depth and other factors on choosing the most suitable equivalent circlular method.Finally, referring to the project example to verify the conclusions above and carrying out the non-circular cavity model test research. The surrounding rock stress and displacement of rectangular cavity after excavation is monitored and the corresponding GRC curve of surrounding rock is drew, which is used to do comparative analysis with the approximate GRC curve for rectangular cavity that builded up based on method in the article, in order to further validate the effectiveness and practicality of the proposed method.