Based on the maximum value of the self-stability of surrounding rock, the key issues affecting the distribution of the minimum mock cover thickness of the surrounding rock self-stability (MRCT-SRS) of the metro tunnel in the soil-rock dualistic stratum are discussed. The MRCT-SRS was studied for different soft stratum thicknesses Hs and excavation spans D based on cusp catastrophe theory. Moreover, the 3D spatial distribution was determined, and the fitted curves were constructed according to the MRCT-SRS, Hs, and D. This facilitated the assessment of the stability of the surrounding rock in the excavation of a metro tunnel. Combined with the construction practices used for the Qingdao metro project, the validity of the obtained MRCT-SRS has been verified by the inverse analysis of the monitored data from the metro tunnel. Furthermore, the application of the MRCT-SRS in determining the reasonable buried depth of a metro line has been explored. The research results have provided theoretical support and scientific basis for the preparation, revision, and improvement of the relevant codes, standards, and guidelines for metro tunnel planning and design.

中文翻译：

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土-岩二元地层中地铁隧道围岩自稳定最小覆岩厚度的分布特征

基于围岩自稳定的最大值，影响土石二元地层中地铁隧道围岩自稳定最小模拟覆盖厚度（MRCT-SRS）分布的关键问题是讨论过。基于尖顶突变理论，针对不同的软层厚度Hs和开挖跨度D对MRCT-SRS进行了研究。此外，确定了3D空间分布，并根据MRCT-SRS，Hs和D构造了拟合曲线。这有助于评估地铁隧道开挖中围岩的稳定性。结合青岛地铁项目的施工实践，通过对地铁隧道监测数据的反分析，验证了所获得的MRCT-SRS的有效性。此外，还探讨了MRCT-SRS在确定地铁线路合理埋深方面的应用。研究成果为地铁隧道规划设计相关规范，标准和指南的准备，修订和完善提供了理论依据和科学依据。