Deep tunnel excavation in squeezing rock has strong tendency to asymmetric large deformation under the influence of active fracture zones. Issues, including steel arch twisting, shotcrete cracking and spalling and anchor failure could lead to the damage of the primary support and compression collapse in the reinforced concrete of the secondary lining. In order to explore the mechanism of asymmetric large deformation and control its potential threats, the research team has carried out a series of in-situ tests, including ground stress test, rock sample composition analysis, rock structure surface identification, high-density electrical resistance method test, and surrounding rock loosening zone test in the excavation surface on the Daliangshan Tunnel of Yunlin Highway in Yunnan Province. The research findings show that the geologic tectonics and volcanism could cause an intrusion of the granite into the schist to form the mechanical genesis mechanism of the extruded tectonic stress and lithologic contact zone. According to the yielding principle and the New Austrian Tunnelling Method, the research team has raised a two-scheme proposal for controlling the extrusion deformation of the tunnel based on a comparative study on the two schemes. The results show that the yielding support control scheme could have positive impact on the control of asymmetric large deformation section and the stress distribution of the tunnel surrounding rock. After the adoption of yielding support control method, the stress state of surrounding rock showed reasonable improvement by 32.5% less in the degree of its unevenness at its the largest bearing capacity. This support scheme has also cut down the costs of tunnel support by 10% compared to double-layer rigid primary support scheme. The research method has already been applied to the construction of large deformation section in the Daliangshan tunnel and the nearby Tianshengqiao tunnel.

中文翻译：

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挤压岩中不对称大变形隧道的破坏机理分析及屈服支护控制方法——以实例为例


在挤压岩中开挖深隧道在活动裂隙带的影响下具有很强的不对称大变形倾向。包括钢拱扭曲、喷射混凝土开裂和剥落以及锚栓失效在内的问题可能导致次级衬砌钢筋混凝土的主支撑损坏和压缩坍塌。为探究不对称大变形的机理并控制其潜在威胁，研究团队在云南省云林公路大凉山隧道开挖面开展了一系列原位试验，包括地应力试验、岩样成分分析、岩石结构表面鉴定、高密度电阻法试验、围岩松动区试验等。研究结果表明，地质构造和火山作用可导致花岗岩侵入片岩，形成挤压构造应力和岩性接触带的力学成因机制。根据屈服原理和新奥地利隧道法，研究团队在对两种方案进行比较研究的基础上，提出了控制隧道挤压变形的两种方案方案。结果表明：屈服支护控制方案对不对称大变形断面的控制及隧道围岩的应力分布具有积极影响。采用屈服支护控制法后，围岩的应力状态在最大承载力下其不均匀程度明显改善了 32.5%。与双层刚性初级支撑方案相比，该支撑方案还将隧道支撑成本降低了 10%。 该研究方法已应用于大凉山隧道和附近天生桥隧道大变形段的施工。