Abstract The limit state equation for the design of a tunnel portal structure is transformed into a practical design expression using a partial factor for the sake of convenience in terms of design and inspection. No effective expression is available for use in design when it’s necessary to consider the effect of a seismic load. Based on calculations and review of many standard drawings for a tunnel portal, a principle is proposed to modify the partial coefficient based on a common design expression for tunnel portals in order to meet requirements for tunnel portal design in an earthquake zone. The results show that: 1) the target reliability index for the stability of a tunnel portal structure is determined to be the smallest, so it is the weak point of the structure; 2) the objective reliability index of the tunnel portal structure is determined by a limit state calculation and related industry specifications; 3) the partial coefficients of the load effect and structural resistance for the general tunnel portal structure are determined by many calculations from standard drawings of tunnel portal structures; and 4) when earthquake effects should be considered,the partial coefficient of earth pressure in the design expression for the general structure can be multiplied by 1.9/1.6 so that the effects of the horizontal seismic force and changes of the internal friction angle of the soil can be avoided.
Abstract：
The limit state equation for the design of a tunnel portal structure is transformed into a practical design expression using a partial factor for the sake of convenience in terms of design and inspection. No effective expression is available for use in design when it’s necessary to consider the effect of a seismic load. Based on calculations and review of many standard drawings for a tunnel portal, a principle is proposed to modify the partial coefficient based on a common design expression for tunnel portals in order to meet requirements for tunnel portal design in an earthquake zone. The results show that: 1) the target reliability index for the stability of a tunnel portal structure is determined to be the smallest, so it is the weak point of the structure; 2) the objective reliability index of the tunnel portal structure is determined by a limit state calculation and related industry specifications; 3) the partial coefficients of the load effect and structural resistance for the general tunnel portal structure are determined by many calculations from standard drawings of tunnel portal structures; and 4) when earthquake effects should be considered,the partial coefficient of earth pressure in the design expression for the general structure can be multiplied by 1.9/1.6 so that the effects of the horizontal seismic force and changes of the internal friction angle of the soil can be avoided.
2018, Vol. 55 