For up bamboo-truncating tunnel portal without obvious wall-style structure

there is no existent design method and structure checked mode in present code. In this paper

aiming at bored method and open-cut method for portal section

3D FEM numerical analysis method is adopted to study the mechanical behaviors and design method of tunnel portal section. The research results show that: Choosing 42 m as the length of portal section and designing as a whole could be reasonable; In the shallow burying section of the extension of 28 m

the surrounding rock pressure of lining crown increases with the increase of depth of tunnel; and pressure of the bored tunneling method tunnel is maximal

the calculation result following the method of the railway tunnel code is the second; and the pressure of the open-cut method is minimal; When taking open-cut method

in the longitudinal direction of the extension of 42 m of portal

the mechanical behaviors of lining crown shows some characters of stringer bending

part of crown is in bended-pulled state; the internal force shows a three-dimensional effect

and the internal force of the direction both transversal and longitudinal should be checked for structure; when taking bored method

the internal force checking is only considered for transversal direction; when the excavation condition allows

the bored method is suggested to do portal tunneling by the reason that this tunneling method can improve mechanical behaviors of tunnel portal structure effectively.