Abstract: To guarantee the renovation effect of railway tunnel lining cavity under bad geological conditions, based on practical renovation cases, the causes of lining cavity, the approximately standard flowbased renovation technical solutions, the safety calculation of lining structure with bad geological conditions, renovation effect assesment, etc. are studied. The results show that：（1）Lining cavity is mainly caused by bad geological effects (i.e. groundwater erosion and karstification) and construction quality problems (i.e. uneven initial supports, vault cavity and human factor); (2) Through checking calculation of structural safety and nondestructive testing of geological radar and lining strength experiment, it is proved that the comprehensive renovation concept and method system of railway tunnel lining cavity established have good effect.

Key words: railway tunnel, cause of lining cavity, renovation scheme, numerical calculation, lining cavity