Local buckling characteristic of hollow π-type steel-concrete composite support in hilly-gully region of loess tunnel

•The deformation and the pressure from surrounding soil affected by the “U” shaped terrain were analyzed.•The failure mode, bearing capacity, and deformation characteristics of the arch under different gradient distributed loads were systematically studied.•The structural parameters of the steel frame were comprehensively analyzed and optimized.•The corresponding anti-buckling measures and concrete pouring scheme were proposed.