Enhancing airtightness performance of concrete tube transportation systems: A prestressing perspective

The Super-Speed Tube Transportation System (SSTT) transforms the transportation landscape by employing semi- vacuumed tube structures to propel vehicles at exceptionally high speeds. The key to achieving optimal operational efficiency lies in maintaining airtightness, as any air leakage can detrimentally impact performance. This paper investigates the influence of prestressing on system airtightness, utilizing a combination of experimental techniques and finite element analysis (FEA). The experimental approach involves constructing a scaled concrete tube specimen subjected to displacement-induced loading, with measurements of effective intrinsic air permeability (keff) and changes in pressure within the tube structure to evaluate airtightness performance. Results indicate a significant improvement in airtightness achieved through prestressing with longitudinal and external circular confinement (PC-CF), although it also led an abrupt failure under higher displacements due to increased brittleness. FEA further investigates various concrete tube models, elucidating the correlation between airtightness and prestressing force. A parametric study reveals that increased compressive strength enhances airtightness up to a certain threshold, but high-strength concrete poses a risk of cracking. Longitudinal prestressing alone had marginal impact, while circumferential prestressing showed a direct correlation with airtightness improvement up to approximately 5 atm. The study underscores the direct link between airtightness performance and applied prestressing force, emphasizing the importance of optimal prestress design. This research strengthens the foundation for advancing the performance of SSTT system, providing the valuable insights to contribute for the development of more efficient and sustainable transportation solutions.