Choosing 20 meters long tunnel with typical wall rock condition as the subject of study

which is a part of the Dujiashan tunnel belongs to the Guang-Gan Expressway and located in the earthquake fault zone of the 5•12 meizoseismal area

and comparing the follow items when there exists systematic bolts or not

including displacement of tunnel inner perimeter

axial force of the bolts

internal force of the steel arch truss

pressure between wall rock and preliminary support

and the internal force of second lining are analyzed. The essay also discusses why the bolts support effect is not evident and proposes to adopt the preliminary support method which is jet steel in broken phyllite tunnel in meizoseismal area. The research shows: for tunnels with bolts

axial force of the bolt is smaller; the final displacement of tunnel inner perimeter and the pressure between the wall rock and preliminary support are large relatively; the safety stock of the steal and second lining is not enough. The process of applying bolts will disturb the deep wall rock to some degree and miss the best time to apply the shotcrete and steel arch truss to support the weak and broken phyllite tunnel. What’s more

the damage to the deeper wall rock and the penetrability of the broken rock mass increase

which result in that wall rock relaxation region exceeds bolt setting range and the cohesive force between bolts and wall rock decreases.