Review and perspective of expressway tunnels in Taiwan, China

Since the construction of the first expressway in the 1970s, the total length of expressways in Taiwan has increased to over 1 000 km, of which 40 km are aligned with tunnels. These twin-tube tunnels, which have two or three lanes in each tube, are characterized by large cross-sections. Due to the complicated topography and heterogeneous geological conditions of Taiwan, tunnel construction has encountered many difficulties. Thus, many advanced excavation methods were developed during tunnel construction. To satisfy the concurrent requirements of safety, economy and efficiency, new construction methods and techniques should be developed or introduced. Moreover, environmental protection and ecological conservation must be paid increasing attention to the goal of substantial development.