In soft rock tunnels, complex section arches with different composition materials or irregular shapes have been used, but the calculation efficiency of their compressive and bending bearing capacity is not high. Based on the expression of internal force integral, known stress distribution under plastic state, and the division of compression zone and tension zone by neutral axis, this article derives the internal force formula of arch frame characterized by material strength and geometric parameters of section tension compression zone. Based on CAD drawing of arch frame section and rapid acquisition of geometric parameters, a simple calculation method for the bending and compression bearing capacity of complex section arch frame is formed, which is called the drawing method. The compression bending capacity of several different arches was calculated using drawing and formula methods. The results show that for the ultimate axial force and ultimate bending moment of the arch section, the difference between the calculation results of the drawing method and the formula method is not more than 5%, and the compression bending capacity curves of the arch obtained by the two methods are basically consistent. The research results can provide reference for the selection of arches for soft rock tunnels.
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