Abstract： Cracking and disengaging are the main diseases of rail transit. Between them, the latter is a great threat to operating driving safety, which will threaten the driving safety and stability, shorten the service life of the track structure, and affect passenger comfort. Due to design constraints, the ballast in the shield tunnel is more prone to occur disengaging disease. In this paper, the causes of the monolithic ballast disease of the shield tunnel are described. The applicable conditions, advantages and disadvantages of the maintenance methods including reinforcement, comprehensive improvement and renovation are summarized. Based on the comprehensive treatment of the Beijing Metro Airport Line from T2 Airport Building to Sanyuanqiao, four key technical points of the comprehensive treatment method for the monolithic ballast are introduced in detail. Results show that the requirements for the hydrophilicity and adhesion of grouting materials are high under wet environment operating conditions. The control of rail facility renovation process must be precise. After the rectification is completed, the subway's normal speed must be strictly controlled. In addition, construction preparations, processes and effects are also detailed. This study provides a reference for similar ballast disease treatment in urban rail transit.
