Abstract: Taking the Xikema no.1 tunnel as engineering background, the reinforcement effect of pre-reinforcement measures including pipe-roof and double-row small duct, is studied through the model test. Some useful conclusions are drawn by analyzing the change law of stress and displacement of surrounding rock in different pre-reinforcement measures during the excavation, The research results show that: (1) In the tunnel longitudinal direction, pipe-roof and double-row small duct play a role of supporting beams; they can primely control the above surrounding rock loose caused by tunnel excavation and reduce surrounding rock stress above the work face, so as to guarantee the stabilization of the work face. (2) In the tunnel on the transverse, pipe-roof and double-row small duct can form into a complex well with surrounding rock, which plays a role of load-bearing arch to limit the above surrounding rock stress release and improve the safety of the supporting structure. (3) The longitudinal beam effect of pipe-roof is stronger than double-row small duct; but the transverse arch effect is weaker than double-row small duct.

Key words: shallow tunnel with large cross, similarity model test, pre-reinforcement measures, beam-arch effect