To address the technical challenges associated with the design and construction of large-section single tunnels in water-rich basalt with tuff strata, such as the determination of construction methods and support parameters, a comprehensive study was conducted. This study was based on a new high-speed railway tunnel project in Yunnan Province and employed engineering investigation, field monitoring, and numerical simulation to examine the deformation and control technology of the surrounding rock. The results indicate the following:(1)Implementing initial support immediately after excavating the upper bench using the two-bench method significantly reduces the crown settlement rate, achieving a final settlement of approximately 38.5 mm, thereby effectively limiting further deformation of the arch base.(2)During excavation, horizontal deformation is concentrated at the arch foot and waist. After excavation, the maximum horizontal displacement shifts downward to the arch wall, with the affected area expanding outward in a butterfly-like pattern. In the two-bench method, the monitoring points at the upper and middle benches exhibit greater clearance convergence values and rates compared to the three-bench method, whereas the lower bench shows smaller values. Additionally, the rapid closure of the invert in the two-bench method results in superior deformation control.(3)Tunneling through strata with high water content creates a dewatering funnel, where groundwater seeps out along the tunnel face and benches. The two-bench method reduces the initial support closure time, leading to decreased dewatering. However, it results in the formation of a high-pressure zone above the crown.(4)The installation of additional drainage pipes can mitigate the load on the lining structure. Furthermore, the integration of mechanized construction techniques with the two-bench method has approximately doubled the average monthly construction progress.
我国西南山区地层复杂多变,特别是云南地区玄武岩与凝灰岩接触带,玄武岩节理裂隙发育,地表水通过裂缝向下渗透,极大地降低了围岩力学性能,易出现隧底承载力不足、塌方、涌水突泥和初支大变形等问题,给铁路隧道建设带来极大的安全隐患(Sun et al,2023;Song et al,2025)。隧道开挖工法经过长期的实践与发展,针对不同的隧道围岩等级,形成了较为全面的施工工法体系。《铁路隧道设计规范》(TB10003-2016)规定:Ⅳ级围岩推荐采用台阶法或分部开挖法(国家铁路局,2017)。在两台阶法、两台阶预留核心土法、三台阶法、三台阶预留核心土法和CD法(Cross Diaphragm Method)等不同开挖方法在软岩地层变截面铁路隧道围岩变形控制中,三台阶预留核心土法可有效控制围岩变形(普红祥等,2023;梁淦波等,2024)。
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