Abstract: To improve the support reliability of gripper of tunnel boring machines(TBMs) boring in broken and weak surrounding rocks and determine quantifiable judgment basis, corresponding treatment measures are formulated and standardized to ensure tunneling efficiency. Based on TBM structural design and excavation parameters of a case project, the forces of TBM propulsion and support system are analyzed, the bearing capacity model of surrounding rock for gripper is established, and the bearing effectiveness of direct support of surrounding rock and treatment of square wooden cushion support is calculated. The results show the following: (1) The effective contact area between gripper and rock mass can be used as the main characteristic quantity for passability judgment. (2) The allowable contact area between gripper and rock mass under the strength criterion shall be guaranteed preferentially. (3) The flaking area of grades I and II surrounding rocks relative to gripper is not the main factor causing gripper slip during treatment of square wooden cushion support. Finally, four kinds of treatment measures and key points are formulated in conjunction with engineering practice. To improve the identification ability of gripper for unfavorable geology, appropriate treatment measures and moulding reduction have good application effect.

Key words: open tunnel boring machine, tunnel surrounding rock, unfavorable geology, support and reaction force of gripper, permissible contact area