Performance evaluation of airtightness in concrete tube structures for super-speed train systems

Abstract

A super-speed tube train (SSTT) system is a conceptual alternative transportation system where trains could operate with a practical speed as high as 700 km/h in a vacuum tunnel, which minimises air resistance. This paper presents the results of a preliminary study involving an airtightness performance evaluation of a concrete vacuum tube structure for an SSTT. A formula for determining the flow rate of the air movement caused by the pressure difference inside and outside the tube structure is derived on the basis of Darcy's law. A material test is performed to measure the air permeability of concrete with various compressive strengths. A large-scale experimental study is then conducted for concrete tube structures with various joint configurations to investigate the suitability of concrete tube structures for an SSTT system. The results show that, as expected, a structure with more joints or bonds tends to be less airtight. A sensitivity study shows that the system's airtightness performance level increases with an increase in either the diameter or thickness of the tube. Moreover, an increase in the diameter or thickness of the tube enhances the effectiveness of any approach used for improving the airtightness of the system.