高地应力红层软岩隧道大变形分级控制技术研究

Research on Large Deformation Grading Control Technology for High Stress Red Layered Soft Rock Tunnels

高地应力红层软岩是我国西南地区隧道建设中常见的不良地质,隧道穿越这类地层时常发生挤压大变形现象。以玉磨铁路新华隧道穿越高地应力红层软岩段为工程背景,基于现场地质条件、结构破坏特征、变形监测数据分析大变形灾变成因,并提出高地应力红层软岩隧道大变形分级控制技术,通过数值模拟和现场应用验证分级控制方案的有效性。研究结果表明:新华隧道大变形段地层属典型红层软岩,围岩变形具有变形速率大、变形量大和持续时间长等特点,并伴有初期支护开裂脱落、钢拱架变形扭曲、初期支护侵限、小导管失效等情况;新华隧道大变形主要是高地应力、软弱地层条件、红层软岩应变软化和扩容膨胀效应以及支护不及时等因素耦合作用导致的;根据围岩强度应力比,将现场大变形等级分为轻微大变形、中等大变形和严重大变形3个等级,针对不同变形等级提出大变形分级控制方案,数值模拟和现场应用情况显示变更后的控制方案能够显著降低围岩变形,3种控制方案下围岩变形均在预留变形范围内。

High-stress red layer soft rock is a common adverse geological condition in tunnel construction in Southwest China,where tunnels often experience large deformation caused by extrusion when passing through such strata.Taking the Xinhua tunnel on the Yuxi-Mohan Railway,which passes through a high-stress red layer soft rock section,as the engineering background,this study analyzes the causes of large deformation disasters based on field geological conditions,structural damage characteristics,and deformation monitoring data.It proposes a graded control technology for large deformation of soft rock tunnels in high-stress red layers.The effectiveness of the control scheme is verified through numerical simulation and field application.The research results indicate that the stratum of the large deformation section in the Xinhua tunnel is a typical red layer soft rock with characteristics such as high deformation rate,large deformation magnitude,and prolonged deformation duration.Issues like cracking and detachment of initial support,deformation and twisting of steel arch frames,encroachment of initial support,and failure of small conduits were observed.The main causes of large deformation in the Xinhua tunnel include the coupled effects of high in-situ stress,weak strata conditions,strain softening,and volume expansion effects of red bed soft rock,as well as untimely support.The large deformation was categorized into three levels:slight,moderate,and severe,according to the stress-to-strength ratio of the surrounding rock.For each deformation level,a corresponding control scheme was proposed.Numerical simulations and field applications demonstrated that the adjusted control schemes significantly reduced the deformation of the surrounding rock,with the deformation of the surrounding rock within the reserved range under all three control schemes.