The study mainly discusses the mechanical behavior of cobble rock mass during tunneling in Chengdu metro line 1. Cobble rock mass could be regarded as an assembly of discrete particles with the micro parameters of the rock mass have a significant impact on its macro mechanical behavior. Due to the characteristic of such rock mass, conventional study method in continuous medium is no longer available, thus in the study granular discrete element method (basically particle follow code) is applied. The results show that when supporting force is relatively low at the tunnel face, being not able to maintain the stability of the face, then large displacement happens in the frontage of the heading, and the stress of the rock mass is loosened. With time lapse, displacement becomes larger and the loosen area of the rock mass extends, and then tunnel face collapses. With the help of Chengdu metro line 1 project, it proves that PFC is applicable in analyzing the mechanical behavior in cobble rock mass during tunneling.
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