Characteristic analysis of tunnel collapse arch in weak rock mass

The stress of surrounding rock and supporting structure is very complicated during the construction of a loose rock tunnel. The characteristics analysis of collapse arch is very important for the construction safety. This paper compares and analyzes the applicability of the full section method and the three-step method under shallow buried loose surrounding rock, reveals the influence law of tunnel excavation height span ratio on the stability of a pseudo-collapse arch of surrounding rock under shallow buried loose surrounding rock, and rationally chooses the three-step method as the dominant construction method of tunnel construction under this geological condition. For the three-step construction method, the optimization study of the excavation height of the upper step is carried out, the relationship between the excavation height of the tunnel and the stress concentration area under the condition of shallow buried loose surrounding rock is revealed, the influence of surrounding rock stress release on the stability of the tunnel surrounding rock is explored, and the damage of tunnel rock mass caused by the stress concentration phenomenon is analyzed. It is determined that the optimal excavation height of the upper step is 0.4H under the geological conditions of the DS project in Sichuan province, China, under construction. This paper analyzes the influence of structural plane spacing on the stability of a tunnel collapse arch under shallow buried loose conditions and reveals the law that the smaller the structural plane spacing, the worse the self-bearing capacity of the collapse arch, and the higher the risk of engineering accidents such as rock collapse or even collapse in the tunnel, which effectively guides the safe construction of the tunnel under shallow buried loose geological conditions.