Understanding the deformation mechanism and behaviour of adjacent tunnels subjected to dynamic train loads provides vital technical insights for engineering design. This study conducted a detailed analysis and revealed that tunnel excavation significantly affects the stability of adjacent existing tunnels under dynamic loads. First, we developed a dynamic load simulation approach and derived a calculation formula for shield-soil friction. A methodology for analyzing the stress in the surrounding rock of the tunnel was established. Subsequently, the impact of dynamic loads on the stability of existing tunnels was assessed through numerical simulations. Finally, the numerical results were compared with field-measured data to validate the reliability of the research findings. The results indicated that, compared to the condition without train load, the maximum vertical and lateral displacements at the vault of the existing tunnel under dynamic load condition increased by 2.9 mm and 1 mm, respectively, leading to an overall safety and stability coefficient reduction of approximately 0.1. Furthermore, the influence of dynamic loads on the stability of the existing tunnel intensified with increasing train speeds under various load conditions. For train speeds of <= 40 km/h, the dynamic load could effectively be considered as a static load. Notably, the surrounding soft rock exhibited a higher degree of stress release compared to the surrounding hard rock. The stresses at the soft-hard rock interface were found to potentially induce damage to the tunnel. In scenarios where new and existing tunnels were in proximity, the dynamic load was incorporated into the entire simulation process, yielding results that closely aligned with actual measurements.

The internal replacement pipe (IRP) is a developing trenchless system utilised for restoring buried steel and castiron legacy pipelines. It is crucial to ensure that this advanced system is appropriately designed to reinstate the functionality of damaged pipelines effectively and safely. The present paper investigates the structural response of IRP systems used in repairing pipelines with circumferential discontinuities subjected to seasonal temperature changes. Analytical and numerical approaches verified via experimental data and available closed-form solutions were implemented to analyse a total of 180 linear and nonlinear finite element (FE) simulations. A set of analytical expressions was developed to describe the loading and induced responses of the system. Based on an extensive FE parametric study, five modification factors were derived and applied to developed analytical expressions to characterise the structural response incorporating the effects of soil friction. Results showed that there is a major difference between the results of linear and nonlinear analyses highlighting the importance of including the material nonlinearities in the FE analysis. A significant difference was observed between the discontinuity openings with and without the consideration of soil friction implying that appropriate inclusion of soil friction in the FE model is crucial to get realistic system responses subjected to temperature change. Although the application of IRP holds immense promise as a trenchless solution for rehabilitating legacy pipelines, the lack of established design procedures and standards for these technologies has restricted their application in gas pipelines. Results obtained from numerical and analytical models developed in the present research will provide valuable insights for the design and development of safe and efficient IRP systems urgently needed in the pipeline industry.