The double pilot tunnel method is one of important excavation means for the super big cross-section and large-span road tunnel. It will reduce the excavation area of tunnel face

decrease the construction difficulty and increase the integral stability of tunnel. However

none unified design criterion of the double pilot tunnel method is available. Especially

it will bring out distinct subjectivity to devise the curvature radius of core-soil temporary support. Furthermore

from practice of tunnel construction

it is found that the curvature radius of core-soil temporary support influences stability of tunnel significantly. Therefore

bases on Longtoushan road tunnel with four traveled lanes in each separated hole

the rational curvature form of core-soil temporary support is discussed and studied mainly with numerical analysis

measured data and illustrations in same boundary condition. The purpose of the article is to provide reference for design and optimization of the super big cross-section and large-span road tunnels.