基于实测数据的穿越软塑黄土层大断面隧道围岩与支护动态作用机制

选取软塑黄土层分布于隧道拱顶、洞身和隧底3组典型断面开展实测研究，分析了软塑层影响下的围岩变形特征、支护结构力学特征及其差异性，提出了基于实测数据确定支护特性曲线的方法，揭示了软塑黄土层影响下的围岩与支护动态作用机制，给出了相应的防控理念及措施。分析结果表明：隧道围岩变形由大到小依次为软塑黄土层分布于拱顶段、洞身段和隧底段；软塑黄土层分布于拱顶段支护结构拱肩和边墙脚、洞身段拱腰及其以下位置、隧底段拱部和仰拱承受较大围岩压力作用；支护结构承受主要荷载来压方向不同、围岩应力随开挖步序释放率不同及地下水渗流路径不同是3组断面支护结构应力存在差异的直接原因；软塑黄土层分布于拱顶和洞身段时，围岩超前应力释放率约为35%，上台阶开挖支护结构力学性能迅速恶化，软塑黄土层分布于隧底段时，下台阶开挖软塑黄土层对支护结构将产生显著影响；针对上述3类工况，提出的强支护、控侧压和防突沉的防控理念及超前帷幕注浆、大锁脚和基底袖阀管注浆等施工控制措施可有效避免施工灾害的发生。

Dynamic mechanism of surrounding rock and support of large-section tunnel passing through soft-plastic loess layer based on measured data

Three groups of typical sections with soft-plastic loess layer distributed in the tunnel crown, tunnel body, and tunnel bottom respectively were selected for testing. The deformation characteristics of surrounding rock under the influence of soft-plastic loess layer, the mechanical characteristics of support structure, and their differences were analyzed. The method to determine the characteristic curve of support based on the measured data was proposed. The dynamic mechanism of surrounding rock and support under the influence of soft-plastic loess layer was revealed, and the corresponding control concepts and measures were offered. Analysis results show that the deformation of surrounding rock in descending order results from the soft-plastic loess layer distributed in the tunnel crown, tunnel body and tunnel bottom. The soft-plastic loess layer distributing in the arch shoulder and side wall of support structure of the tunnel crown, the arch waist and its lower positions, and the arch and inverted arch of the tunnel bottom, bears greater pressure of the surrounding rock. The direct reasons for the difference in the stresses of the three sections are the different directions of the main load of the support structure, the different release rates of the pressure of the surrounding rock with the excavation sequence, and the different seepage paths of groundwater. When the soft-plastic loess layer distributes in the tunnel crown and tunnel body, the release rate of advance stress of the surrounding rock is about 35%, and the mechanical properties of the support structure deteriorate rapidly after the upper bench excavation. When the soft-plastic loess layer distributes in the bottom of the tunnel, the excavation of soft-plastic loess layer in the lower bench significantly impacts the support structure. For the above three types of working condition, the control concepts of strong support, lateral pressure control, and sudden settlement prevention and the construction control measures such as the advance drapery grouting, large feet-lock pipe and sleeve valve pipe grouting at the bottom of the foundation, can effectively avoid disasters in construction.