The design of reasonable flat ratio and distance of large-span twin tunnels with small clear spacing has very important effect on cost saving and improving line’s type planning. Therefore

optimizing the flat ratio and distance of large-span twin tunnels with small clear spacing is the key problem in tunnel design and construction. Program with the standard design language Python of general-purpose finite element software ABAQUS to achieve parametric design for the different flat ratio and distance of large-span twin tunnels with small clear spacing planned to be constructed. Choosing excavation area

plastic zone

ground surface settlement

vault subsidence

etc. as optimal objective

the finite element optimization analysis program combining exact penalty function method and Nelder-Mead optimization algorithm are used to calculate the parametric model. The optimal combination of flat ratio and distance of twin tunnels under supported project is presented. The results and method of this paper have important practical significance for promoting the development and application of large-span twin tunnels with small clear spacing.