关于高原铁路某隧道敞开式TBM开挖直径的探讨

为探讨高原铁路某隧道不良地质条件下敞开式TBM开挖直径是否适应的问题，结合已建、在建工程存在的问题及施工数据，分析TBM法隧道初期支护变形侵限的原因，且通过对比分析工程地质数据、衬砌参数，认为不良地质条件下TBM护盾收缩及初期支护体系形成支护能力周期长是造成初期支护侵限的主要原因。预测当TBM开挖直径为10.2 m时，该高原铁路隧道TBM段Ⅲ级围岩中等及以上岩爆段、Ⅳ级围岩（节理密集带）、Ⅴ级围岩（蚀变岩）存在初期支护侵限的风险。提出如下建议： 1）设计TBM开挖直径时考虑护盾收缩量； 2）在强烈岩爆段、节理密集带、蚀变岩等情况下，采用钢管片施作初期支护以提供临时支撑，缩短支护能力形成周期，并将TBM开挖直径适当增大为钢管片安装预留空间。

Discussion on Open TBM Excavation Diameter of a Plateau Railway Tunnel

To investigate the adaptability of an open tunnel boring machine(TBM) excavation diameter to unfavorable geological conditions in plateau areas, the reasons for limit invasion caused by primary support deformation in the TBM tunnel are analyzed using existing problems and construction data from the completed and under construction projects. The above mentioned data and lining parameters are compared with those in the case study of a plateau railway tunnel. It is discovered that TBM shield shrinkage and the support capacity formed using primary support system are the key causes of limit invasion for primary support under unfavorable geological conditions. Furthermore, when the TBM excavation diameter reaches 10.2 m, the sections with medium and above rockburst in grade Ⅲ surrounding rock, the joint intensive zone of grade Ⅳ surrounding rock, and the altered rock area of grade Ⅴ surrounding rock are expected to be prone to limit invasion. Therefore, the following suggestions are made: (1) Shield shrinkage should be considered when designing TBM excavation diameter. (2) Steel segment can provide temporary support for primary support in strong rockburst sections, dense joint zone, and altered rock and shorten the formation time of support capacity; The TBM excavation diameter should be increased to provide space for steel segment installation.