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  Evaluation of Tunnel Lining Structures Built in Expansive Rocks Considering Ground Water Effect

  The construction of tunnels excavated in expansive and water-rich rocks involves significant concerns for the safety of lining structures. This paper focuses on an ongoing tunnel excavated in silty mudstone within water-rich strata. Laboratory mechanical test and mineral composition analysis are conducted to investigate the expansive characteristics of rocks. It is analysed that the rocks contain clay minerals and exhibit medium degree of expansibility. The ground water pressure acting on the lining structures is estimated based on drilling hole data and empirical criterion. Numerical simulation is then carried out to model tunnel excavation and lining structure performance subjected to various load combinations corresponding to different design profiles. It is found that different tunnel profiles lead to different stress distributions in lining structures and the thicker concrete lining yields smaller stress magnitude. In general, the expansibility of silty mudstone and ground water pressure both have notable impact to the safety of lining structures. Based on extensive calculation results obtained from various design scenarios, the design of tunnel lining structures is optimized and the most beneficial scheme regarding tunnel profile and lining thickness is recommended. The results are hoped to provide useful reference for tunnels built in rocks with similar geological conditions.

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