Abstract：Aiming at the normal and safe work of Songhua river tunnel in Harbin which will be built recently，and using optimum analysis of a factorial experiment，the FEM models which approximating the actual problems on 54 different cases assumed are established and repetitive calculations are carried out to research the relations between various factors and the safety roof thickness of tunnel and to screen out the main affecting factors of safety roof thickness of tunnel；Considering soil-liner interaction，the soil and liner are assumed to be homogeneous，elastic-plastic，continuous，isotropy medium. It is found that the main affecting factors consist of hole diameter，altitude of water，elastic modulus of soil，unit weight of soil，Poisson’s ratio of soil，cohesion of soil，angle of internal friction of soil，elastic modulus of liner，thickness of liner. And then，a stepwise regression analysis method is adopted to obtain the forecasting mathematical model on the safety roof thickness of tunnel which is capable of synthetically embodying the combination action of all main affecting factors. The model’s reliability and efficiency are verified by a calculation example of underwater tunnel.
