OPTIMIZATION RESEARCH ON TUNNEL CROSSING SCHEME THROUGH ULTRA-SHALLOW AND LARGE-BIAS SECTIONS BASED ON ECONOMIC SAFETY COEFFICIENT RATIO

There are many gullies in the loess plateau region.A most unfavorable topographic condition occured when tunnels passed through the gully region.It meaned that tunnels needed to pass through the ultra-shallow and large-bias sections.In order to obtain the economic and safe crossing scheme,the conception of economic safety coefficient ratio and its calculation principle was brought forward.Firstly,the tunnel crossing schemes through ultra-shallow and large-bias sections were designed.The economic safety coefficient ratio of each tunnel crossing scheme was calculated by the methods of strength reduction method and related quotas.Besides,the tunnel's rock stress,deformations and the primary support's stress were simulated and compared among the three tunnel crossing schemes.Finally,the counterweight fill method was considered to be the best crossing scheme,with which the ultra-shallow and large-bias tunnel was in the steady state during the construction period.Good results were achieved so as to offer reference for the future similar projects.