Numerical Simulation of Optimization Construction Method for Soft and Fragmented Surrounding Rock Segment of Tunnel

The surrounding rock of Dawangding tunnel has characteristics of soft and fragment,shallow buried depth,many difficult construction steps and easy collapse.In order to ensure a successful and safe construction in the bad geological conditions,choosing the K43+842 near the left exit of the tunnel as the typical fault surface,FLAC is used to build the numerical simulation model.And then the effect on the surrounding rock displacement and the plastic zone size of four construction methods including full section method,top and bottom shoulder method,three shoulder method,double pilot tunnel method are analyzed and compared.The results show that the total control effect on surrounding rock displacement and the construction quality with double pilot tunnel method is the best and this method is fit for the construction of Dawangding tunnel in the V-level surrounding rock shallow-buried section.