Analysis Of Interaction Between Parallel Tunnel Excavations And Its Application

As an economic and effective tunnel structure, parallel tunnels are more and more adopted in practical projects, especially in the construction of subway. Due to there are many influence factors in which the mutual restriction relationship are existed, the interaction between parallel tunnels is a very complicated problem. So it is urgent to make a comprehensive and systemic research on the interaction between parallel tunnels. In the thesis, based on summarizing and absorbing the research achievements of pioneer works, the theory solution for deformations of an elastic half plane with twin circular tunnels is put forward. Furthermore, the degrees and rules of the interaction between parallel tunnels are studied systemically with the numerical analysis. The main research work of the dissertation can be summarized as follows:1. Based on the study of some references, the characteristic of the construction of parallel tunnels are discussed in details from different points of view, that is, the determination principle of the distances between parallel tunnels, the stability analysis of surrounding rock under the excavation of parallel tunnels, the influence factors of interaction between parallel tunnels and the ground surface settlements caused by the construction of parallel tunnels. Furthermore, the forty-one different ground surface settlement curves, obtained by the field measure of some practical twin shield parallel tunnels projects at abroad and home, are analyzed and the characteristics of the ground surface settlement curves induced by shield twin tunnels are summarized .2. A theory solution is discussed of the class of problems of an elastic half plane with twin cavities, loaded on the cavity boundaries. The solution uses complex variables and alternating method and successfully achieved by the program with computer. The stress distribution and displacements can be determined by this method. And the results are confirmed by a practical engineering case.3. Applying the theory method, the ground surface settlements and distribution of stresses on the middle-rock-pillar, induced by the excavation of twin circular cavities, are discussed under the different conditions with various distances between two tunnels or various depths. Moreover, the results are compared with two plus results of single cavity. Finally, some diagrams are presented which can reflect the difference of results obtained by two methods. With these diagrams, the degrees of the interaction between parallel twin tunnels can be judged directly.4. Based on the different shape of tunnels after excavated between parallel twin tunnels and single tunnel, the convergence mode, which can be adopted by small spacing parallel twin tunnels, is put forward and the relative functions under polar coordinate is derived. Moreover, the reliability of this convergence mode is confirmed by a practical engineering case.5. Based on the practical conditions of the construction, the behaviors of parallel twin tunnels are investigated using a commercial program FLAC. Fifty cases are analyzed considering the influence of three major factors on the interaction between parallel twin tunnels, i.e. the distance between tunnels, the grade of surrounding rock and the depth of tunnels. Under the influence of each factor, the different characteristics of the distribution of internal force on the lining of parallel twin tunnels, induced by the interaction between tunnels, are mainly discussed.6. The evaluation method for the safety of the tunnel lining is put forward. And it is successful used to the practical multiple tunnels engineering project and the influences of the construction of adjacent parallel tunnels on the safety of the existing tunnel are evaluated in effect.7. Based on the field measurements of twin parallel tunnels excavated in horizontally intervedding rocks on ChangJi highway in Hunan Province, the numerical model is performed. From the results, the influences of the different distances between two tunnels and the various surrounding rock conditions on the mechanics character of the construction of twin parallel tunnels are studied. Furthermore, an evaluation method for the stability of middle rock pillar is proposed. Finally, the results are directly used to guide the practical construction of tunnels and the satisfied effect is achieved.