Abstract: A mountain tunnel in western China that is subject to poor geological conditions, shallow buried depth and unsymmetrical pressure encountered a chimney collapse event caused by inappropriate construction and an unreasonable construction method. During the remediation process, surface sealing was used for loose masses, and advanced reinforcement was also adopted using the forward segmented condulet grouting technique based on the “shallow-buried bored excavation method”. According to the collapse treatment principle of “reinforcing the back non-collapsed section, sealing the rock surface and stabilizing the collapsed rock masses,” steel arches and long anchor bolts were used to reinforce the non-collapsed section to prevent the expansion of the accident. For the collapsed sections, the up-and-down bench + reserved core-soil method was used for ring excavation while heavy support was implemented with small-spacing steel arches. According to the feedback of numerical simulation and on-site monitoring data, all the treatment measures are rational and effective and may provide a reference for treatment in similar projects.