| The fast development of urbanization and construction technology improvement provide the development platform for underground interchange, make it become a new development direction to solve the problem of urban transport. However, the characteristics of large span, complex structure in underground interchange has led to the phenomenon of new tunnel construction near the existing tunnel. Consequently, rock and soil mass around existing tunnel will be disturbed again and a series of mechanical behavior changes will be caused. If left untreated, it would produce unfavorable effects on existing tunnel. On the basis of previous research, with the support of the planning two-river tunnel engineering in Chongqing, this dissertation conducts systematical research work on the mechanical behaviors of an existing tunnel during the excavation of new tunnel by the research method combined with the similar simulation test and the numerical simulation analysis. The main research achievements are as follows:â‘ On the basis of the similarity theory, combined with project fact of two-river tunnel project, similarity model test research on underground interchange tunnel have been carried out. The similarity ratio between the model and its prototype of interchange tunnel has been constructed, and the mix ratio of simulation materials for existing tunnel support and surrounding rock have been proposed. Furthermore, according to basic mechanics theory of single circular chamber, measuring system and its layout have been established, and boundary loads have been designed.â‘¡The similar model tests were carried out to dynamically simulate the new undercrossing tunnel excavating process in the interchange tunnel. The changing rule of surrounding rock deformation, stress and interior mechanical behaviors of the supporting structure on the two vertical sections of the existing tunnel are studied. The results show that the existence of existing tunnel support has some restriction effect on surrounding rock deformation. New tunnel construction has more influence on sections at the intersection and wider impact of sections at both sides of the cross position.â‘¢Based on the finite element theory and combined with the established interchange tunnel model, the new undercrossing tunnel excavating process is simulated. The changing rule of mechanical behaviors at the four vertical sections across of the existing tunnel within 17 meters of intersection are analyzed, including vertical and horizontal displacement at vault, dome and hance, relative displacement of the surrounding rock, inner force of supporting structure and stresses of the surrounding rock. The results of numerical analysis were compared with real data obtained from laboratory tests, the results show that changing trends obtained with both methods are basically consistent.â‘£Various influence factors on the close-spaced tunnels construction are analyzed. The numerical analysis method is used to study the influences of four different tunnels with different spacing (0.25D,0.5D,0.75D,1.0D) on the mechanical behaviors change of existing tunnel, including stress changes in surrounding rock at intersection, changes of surrounding rock deformation and interior mechanical behaviors of the supporting structure on the two vertical sections of the existing tunnel, the plastic area of surrounding rock and the magnitude of plastic strain. There are some conclusions after comparative analysis: The smaller the spacing distance between two tunnels, the greater the tensile stress area, tensile stress value of the surrounding rock, deformation of tunnel and rock, accessional internal force of supporting structures, plastic area and plastic strain. Plastic zone completely run through the surrounding rock at intersection under the 0.25D tunnel spacing. |
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