Study On Optimization And Stability Evaluation Of Design And Construction Of Forked Tunnel

Forked tunnel is a kind of combining from tunnel that consists of large-arch, multi-arch, neighborhood and transition tunnel. The special structure type and conversion of stress and operation sequence frequently leads to the fact that its excavation and support system is an accumulative difficulty system in complex stress space in tunnel construction. This paper concentrates on how to bring up a global and accuracy description and assessment on the design and construction scheme and further get a universal method. For this purpose, under the background of construction of kiaochow bay subsea tunnel, stability analysis and intelligent global optimization method for forked tunnel is proposed by integrating different theory and technology, such as 3D numerical simulation, bionic optimization, kernel machine learning and catastrophe theory. Specific steps are as follows:Bionic optimization algorithm firstly couples with FLAC for displacement back-analysis of mechanical parameters of surrounding rock. Moreover, PCA and catastrophe criterion are used to cope with weight distribution and stability evaluation respectively. Finally, the global optimum excavation sequence and support parameters are obtained by the new intelligent global optimization method. Thus, the problem mentioned above could be solved successfully based on the new method. Detailed research results include the followings:1. Study on the kernel machine learning and bionic optimization algorithm(1) Gaussian process (GP), the third generation kernel machine, has advantages of small samples, probabilistic reasoning and good generalization capability. The analysis results of displacement nonlinear time series of tunnel and slope indicate it notably improves on the accuracy and efficiency of prediction compared with ANN and SVM.(2) Simulated annealing (SA) with characteristics of'uphill'and'downhill' simultaneously is introduced to improve the standard particle swarm optimization (PSO) for modifying the population diversity and then the new coupling algorithm PSO-SA is proposed. Its application results of function test state clearly that the algorithm is applicable to solve the highly nonlinear problems.(3) For overcoming the shortcomings of conjugate gradient during the process of optimizing the kernel function of machine learning, the PSO-SA instead couples with GP for forming the new PSO-SA-GP algorithm. Compared with the GA-GP algorithm, the new algorithm demonstrates advantages in two areas, namely simplicity and efficiency of code, aiming at predicting the displacement of typical landslide.2. Study on excavation and support optimization based on computation intelligence(1) PSO is used to couple with FLAC2D in order to form the new evolutional finite difference method. Then it is adopted to cope with the back-analysis of mechanical parameters of surrounding rock with the advantages of computational efficiency and optimization accuracy.(2) PCA and catastrophe criterion are used to handle the weight distribution and stability evaluation during the process of optimization on excavation and support scheme respectively. The former can achieve the goal of simplifying the evaluation system and dimension reduction and the latter can be served as a new evaluation index and constraints for multi-objective decision making.(3) Aiming at the global optimization of excavation and support scheme, a new PSO-SA-GPR-FLAC3D method with global parallel search and black-box reasoning is put forward for reducing the cost of large-scale 3D numerical simulation. It can handle the multi-objective decision making well and used as a new way for similar engineering.3. Study on line-shape optimization of transition section and contour design of cross-sectionFirstly, the stepped layout is decided as optimum transition mode based on catastrophe criterion and traditional analysis indexes. Secondly, considering the different speed between main tunnel and ramp tunnel new modified formulas for the lengths of transition section and horizontal line-shape are proposed. Finally, the spatial layout and contour design method of stepped cross-section is got by mapping principle.4. Study on the optimization of design and construction of forked section of kiaochow bay subsea tunnelMechanical parameters of surrounding rock in tunnel site are obtained by PSO-FLAC2D. Then the optimization of excavation and support scheme and stability of tunnels are done by the integrated global intelligent method including the AI, ANSYS and TECPLOT etc. Finally, reasonable supporting parameters, construction sequence, section scale and its spatial layout are provided for builders.