Study On Control Theory And Application Of The Civil Air Defense Tunnel Reconstruction And Extension In City Subway Design

With the rapid development of city construction, more and more attention has been paid to the development and utilization of urban underground space in many cities. The idea of transforming the existing civil air defense tunnels into urban rail transit construction has been brought into important research projects. Differing with the conventional tunnel excavation method, the reconstruction of civil air defense tunnels is through unilateral and bilateral expanding excavation to form new underground space based on the existing section, about which the design theory and basic construction control theory is still a gap. Harbin metro1st project, with the length of14.4km, used the exisiting air defense tunnel, whose scale and complex environment is rare both at home and abroad. Relying on the project, this paper studies the design and controlling theory of digging and transforming the existing civil air defense tunnels into metro.Among the expansion of existing air defense tunnel projects, the destruction of the original air defense tunnel lining, the secondary excavation, and the secondary support must be completed. Through on-site measurements and computational analysis, it is found that the deformation of tunnel support structure between pre-and post enlarging and excavation was small,; but the tunnel lining force changed greatly and the mutual squeezing effect between the support structure and surrounding rock was strong. Thus, based on the limit equilibrium theory, this paper analyzed the limit load caused by the disturbance of the above surrounding rock pre-and post enlarging and excavation, and generated the "load-structure" model which applies to air defense tunnel enlarging and excavation project. With the introduction of gradual release method by applying virtual support force, the combined action of disturbed surrounding rock and the support structure was analyzed. This paper has solved the problem of numerical simulation of the stress release and load transfer during air defense tunnel enlarging and excavation, including the destruction of the original air defense tunnel lining, the second excavation and the second support. Furthermore, the design theory of formation-structure method of civil air defense tunnel enlarging and excavation was established.Through the field test, the design parameters of grouting for rebuilding the existing civil air defense tunnels were studied. Furthermore, the relation between the grouting ring and the stress field and plastic zone were quantitatively analyzed through combineing the numerical simulation with the test results. Therefore the test result could be used to quantitatively predict the construction behavior, and the design theory of advanced support grouting for expanding excavation of the existing civil air defense tunnels was established. Moreover, in this paper the evaluation method for the construction building damage caused by expanding excavation of the existing civil air defense tunnels was presented by taking surface construction, regional rock and supporting structure as a whole geological body.To integrate the tunnel design, construction, monitor and measurement through the aspect of project management, design and control theory, the surface settlement was selected as the major control indicators of expanding excavation of the existing civil air defense tunnels, and the concepts of "previous-construction prediction" and "period-construction prediction" were presented. Based on the random media theory, the previous-construction prediction can be used to predict the surface settlement value under single or double side expanding excavation, by assuming that the tunnel convergence has a non-uniform elliptical cross-section. And in period-construction prediction, the gray-Markov chain forecasting model was established based on probability statistics theory. The model can be used to predict the future settlement value by importing the monitoring result. By combining the two-stage predictions, the design can be optimized more accurately and dynamically, and the information construction can also be implemented.