Analysis Of Elasto-plastic Finite Element And Dynamic Response Of Close-Spaced Tunnels

In recent years, with the development of making use of the underground space by mankind, more and more new tunnels are closely built to traverse the existing tunnels or other structures in some area. The reasons for building close-spaced tunnels are the construction of double-track railway, the limitation of geological condition and existing buildings, and the need of utilizing underground space efficiently. How to ensure the safety of the newly-built tunnel and the normal operation of the existing tunnel is a key problem that we have to solve during the construction process. So it is quite necessary to study the interaction between the close-spaced tunnels in construction.In the thesis, based on the worldwide research achievements, the principle of construction in close-spaced tunnels in different rock conditions are summarized, the degree of stress concentration, the stress and area of plastic zone, the displacement and stress state of the support structure are analyzed systematically. With elasto-plastic theory, dynamics principle and numerical method, two cases of close-spaced tunnels in Wen-Fu railway project which the author has participated in are simulated and analyzed. The main achievements are as follows:(1) For Guantouling tunnel which traverse under the existing expressway tunnel, the construction scheme of the newly-built tunnel near the cross point is studied, including the choice of the excavation method, the working procedure and the assistant construction measures. Based on a three dimensional elasto-plastic finite element model in ANSYS program, the whole construction process of the newly-built railway tunnel is analyzed. The analysis shows the stress and displacement of existing tunnel variation law with constructing of the newly-built tunnel.(2) For Yanqianerhao trumpet-like tunnel, the excavation method and the main techniques of construction control are studied. Based on dynamic principle and failure theory of rock blasting, the dynamic response of the existing tunnel under impact load is analyzed by transient dynamics section of ANSYS program during the blasting excavation of small spacing tunnels. We obtain variation curves of vibration velocity, vibration acceleration, displacement and maximum principal stress with loading time.