Tunnel-Ground Interaction Modelling in Jointed Stratified Rock Masses Under Long-Term High-Speed Train Loading
Authors: Zhang Z. X. , Yang J. Y. , Pan W. B. , Wang S. F. , Lei Q. H. 
Published: August 2024

ABSTRACT:
With the rapid expansion of high-speed railway networks, an increased number of tunnels have been constructed in mountainous areas. To ensure the safety of railway system operation, it is of central importance to assess the performance of rock tunnels subject to cyclic train loading. One of the important challenges related to this problem is that, under dynamic train loading, the structural deformation of high-speed railway tunnel strongly interacts with the response of surrounding rock masses. Train loading could trigger discontinuities to slip as well as the deformation of intact rocks. The above-mentioned geological deformation could in turn affect tunnel structural deformation. Moreover, the long-term strength degradation of rock mass due to chemical weathering could exacerbate this influence. Thus, it is essential to develop a modelling framework that can capture the long-term coupled structural and geological mechanism in the system. Based on the Universal Distinct Element Code (UDEC), we conduct a comprehensive simulation of a 2D circular high-speed railway tunnel located in jointed stratified rock masses. Also, we find that long-term structural deformation is predominantly attributed to the deformation of rock masses (discontinuities and blocky rocks), but the permanent structural deformation is mainly related to the shear displacement of discontinuities. The results have significant implications for the assessment of high-speed railway tunnel performance and the safety of train operation.

1. INTRODUCTION
The rapid expansion of China's high-speed railway networks, such as the proposed Sichuan-Tibet railway line, is placing great demands on tunnel design (Li et al. 2016), one of which is the long-term performance of tunnel structures during the tunnel lifespan (up to 100 years) (Showkati et al. 2021; Wang and Cai 2021). The time-dependent strength degradation of rock masses induced by chemical weathering could have a significant influence on tunnel structural deformation (Idris et al. 2008; Sandrone and Labiouse 2010; Usman and Galler 2013; Showkati et al. 2021), especially coupled with dynamic train loadings and tunnel-ground interactions (Wang et al. 2020, 2022). Discontinuities are widely present in rock masses like stratified sedimentary formations, a typical lithology through which parts of the Sichuan-Tibet railway pass (Chen et al. 2019; Guo et al. 2020). It is expected that the potential shear slippage of these discontinuities subjected to dynamic train loading and long-term strength degradation could play an important role in the long-term structural deformations (Usman and Galler 2013).
The objective of this study is to present a computational framework to investigate tunnel-ground interactions in jointed stratified rock masses subjected to long-term high-speed train loading, considering the time-dependent strength degradation of surrounding rock masses. The remainder of the paper is organized as follows. Section 2 gives a brief description of the numerical model. Section 3 shows the simulation results on long-term responses of discontinuities and tunnel structures. Finally, a short discussion is given and some conclusions are drawn in Section 4.