Abstract: The enlarging or reconstruction requirement of existing tunnel, which can be divided into increases based on traffic flow, new ventilation or escape space, old tunnel reinforcement and so on. Due to the bad conditions of the existing tunnels, including ancient, liningdeteriorated, empty in hole back, weak as time past and deformed, and the lost of design drawing and engineering records, the investigation before designing is very important. In addition, how to consider the use of support and lining of existing tunnel, reduce or lower disturbance of surrounding rock is an important consideration when design and construction. It is difficult to maintain traffic flow during the construction, and the design and construction methods of tunnel enlarging will be very different from new constructed tunnel. The tunnel enlarging methods developed in Japan and Italy are collected and respectively discussed in the form of suitable conditions, limitations and advantages. The enlarging and reconstruction technologies of existing tunnel are further discussed.

Key words: Tunnel enlarging, tunnel reconstruction, adjacent construction