Abstract: The effects of anchors and steel frames on the surrounding rocks are studied by means of ED FEM software ZSoil3D, so as to learn the influence of primary support on the stability of surrounding rocks of tunnel. The calculation results show that: 1) The thickness of plastic zone and the displacement of the surrounding rock tent to decreased as the length of anchor or the moment of inertia of steel frames increased. However, there exists an optimal value of the length of anchor and the moment of inertia of steel frames, beyond which the increase of them does not have obvious influences on the stability of surrounding rocks. 2) The permanent steel frames works as arches that were mainly subject to axial compression except for the localized bending in nodes. Furthermore, the internal force in permanent steel frames was dependent on construction sequences. For instance, the internal force in first assembled members may be several times larger than that in members assembled later. 3) The temporary steel frames are subject to both axial compression and bending. The bending moment in the horizontal members is close to that in vertical members. However, the internal force in the upper and lower steel frames are obviously different. The axial pressure in vertical members of the lower frame is close to that in horizontal members of the upper frame but much larger than that in horizontal members of the lower frame.

Key words: tunnel, anchor, steel frame, moment of inertia, displacement, plastic zone, internal force