Management Of Construction Risk Of Metro Tunnels In Dalian

The being built new Line1of Dalian Metro between Maritime University and High-tech zone is one of the important controlling project. The engineering tunnel transition asymmetric small clear space structure by the large span structures change to the structure, cross-section in the form of separate complex construction process to convert, the construction process of excavation and support mutual influence, surrounding rock stress multiple distribution support and lining structural load conversion complex. In addition, the construction process in the tunnel deformation control difficult, the slightest mistake, it will cause a collapse. Regardless of design or construction, bifurcation tunnel structure is relatively very complicated. Therefore, has important practical significance and value of the works carried out a risk assessment of the construction phase of Dalian Metro.The main contents include:(1) Bifurcation tunnel construction mechanics analysisSix feature sections numerical model, numerical simulation analysis method based on stratigraphic-structural model, forked tunnel simulation of the actual tunnel construction method, analysis of the force-deformation characteristics of the bifurcation tunnel.(2) Bifurcation tunnel construction risk assessSubway tunnel construction risk assessment modeling and application Randomness and fuzziness of the subway tunnel construction risk, the use of fuzzy regression model and neural networks theory to risk prediction. Subway tunnel collapse data through statistical analysis, and summarize the risk factors affect the construction of the tunnel, the main factors were selected as fuzzy regression analysis of the impact factor. Adopt-level analysis and membership functions, respectively, calculated tunneling various risk factors the relative rights weight and risk factors of tunnel construction risk level of membership degree, the various related risk factors of the weight and the risk factors on the level of risk attached to the degree carried fuzzy integrated computing to draw tunnel construction risk level. And research on intrinsic relationship of tunnel security situation.(3) The bifurcation identification and sensitivity analysis of the risk factors of tunnel constructionMain factors establish the model of the hierarchy of the tunnel construction risk factors summarized the bifurcation tunnel construction risk, construction risk factors using the analytic hierarchy sensitivity analysis. Mathematical methods using fuzzy regression and BP artificial neural network to establish the bifurcation tunnel construction risk prediction model. Fixed BP artificial neural network technology, using the negative gradient descent algorithm and using iterative computing to solve network weights heavy and the threshold corresponding network learning memory process, adding hidden nodes so that the optimization problem of adjustable parameters increases, which can be more precise the solution. The assessment system in the process of compiling the built-in core of artificial neural network algorithm, node sample training layers weight threshold input evaluation system, constitutes a complete neural network evaluation model. Based on the current conditions of the tunnel construction risk factors evaluation, the evaluation results into the input layer of the artificial neural network model has been calculated, the output layer evaluation index values of the tunnel. Reference to the the assessment index value calculated will get the size of the tunnel construction risk. The large cross, small clear space and other features section for risk assessment, and risk control management based on the results of the assessment.Through the study, the following results were obtained:(1) The bifurcation tunnel construction the focus is the control of the construction process, reasonable arrangements for the excavation of the two-hole interval and order of support, can effectively control the surrounding rock deformation caused clear distance smaller between the two tunnels, in order to ensure the safety of the tunnel structure.(2) Determine the Dalian metro tunnel construction risk assessment indicators surrounding rock deformation, surface subsidence, the structure of the force, the plastic zone, gushing and landslides. Then regression and artificial neural networks using fuzzy mathematical methods, bifurcation tunnel construction risk prediction model. The large cross, small clear space and other features section risk prediction, risk control management based on the predicted results.(3) Higher subway bifurcation tunnel construction process inherent relationship between the conclusions of the study of the numerical simulation and tunnel security situation and Engineering in situ measured data fit, more comprehensive conclusions of the tunnel construction risk assessment and tunnel construction risk management control subway bifurcation tunnel construction risk, can be used to guide the construction. The measured values are good to make up for the lack of numerical analysis, inspection, and deepen the bifurcation tunneling theory of risk assessment system provides measured data reference for subsequent construction methods and process improvements.