Abstract: When the tunnel boring machine(TBM) used in Daliangshan tunnel of Leshan-Xichang expressway bored to parallel heading No.1 in the layered silty mudstone strata, the surrounding rock loosened and fell, and large deformation occurred. As a result, to investigate the damage characteristics of the surrounding rock during TBM construction in layered silty mudstone strata and explore feasible support methods, the field monitoring and numerical simulation methods are adopted to study the damage process and the factors affecting the stability of the surrounding rock in TBM tunneling in such strata. On this basis, the research of TBM support method is carried out. The results show the following: (1) The deformation and plastic zone of the surrounding rock increase after the shield passes by, the damage of the surrounding rock intensifies, resulting in uncontrollable surrounding rock deformation and plastic zone development under the support of anchor bolt and steel arch frame. The protection zones by anchor bolt and steel arch frame are the key points. (2) The stability of the surrounding rock in such strata is mainly affected by the combination of the layered rock mass formation, high insitu stress, and the unique support method of the TBM. The numerical simulation results of support optimization show that after increasing the rock bolt length and changing the sprayed concrete support method into primary spraying and secondary spraying, the deformation and plastic zone of the surrounding rock have been controlled, the damage has been decreased, and stability of the surrounding rock have been improved, reaching a good construction effect.

Key words: layered silty mudstone, tunnel, open tunnel boring machine, surrounding rock damage characteristics, rock mass stability, support method