The consistency of horizontal alignment at tunnel entrance and exit zone

Current code of tunnel design lacks specific criterion for judging horizontal alignment at entrance and exit zone of highway tunnel.After 3-second freezing of steer wheel,the deviation of the track from the desired path is proposed to evaluate the consistency of horizontal alignment at tunnel entrance and exit,and the control threshold is 0.2 m.The design conditions are classified into three groups and studied in detail.Spiral curve parameter is found to be a significant design index to guarantee the consistency.Then the equations for derivation calculation in different cases are deduced,and the indexes of the horizontal alignment at the tunnel entrance and exit zone are proposed for more flexible design.Based on the research results,an analysis is made of the consistency of the horizontal alignment of a tunnel of Longquan-Qingyuan expressway,and improvement is proposed.