浅埋黏质黄土隧道变形控制机制及措施研究

Deformation Control Mechanism of Shallow-Buried Cohesive Loess Tunnel and Related Countermeasures

为弥补当前超长管棚研究经验及模拟精度的不足,以黏质黄土地层中高铁隧道下穿运营铁路的变形控制方法为研究对象,针对以超长管棚+临时仰拱组成的“纵横支撑”体系的结构受力特征和变形规律开展研究。首先,采用实体单元进行超长管棚的精细化建模,分析地层变形及管棚应力分布规律;其次,运用光栅光纤测试技术实时监测管棚纵向应力,揭示隧道开挖对超长管棚纵向应力的影响范围;最后,分析“纵横支撑”体系的作用机制。研究结果表明:1)整体性好的超长管棚将竖向应力沿纵向大范围转移,减少了掌子面附近钢架应力;2)临时仰拱与开挖后的支护结构形成闭环结构,提升了钢架整体承载能力,有效控制了黄土隧道的变形;3)管棚和支护结构形成的纵横支撑体系中,管棚的最小距离应大于2倍掌子面到支护结构闭合的距离;4)隧道开挖对超长管棚纵向应力的影响范围为掌子面前30 m至后20 m,强影响范围为掌子面前方10 m至掌子面后方5 m,管棚的长度越大,其承载效果越好。

To address the shortcomings of the current research and simulation accuracy of super-long pipe sheds,the structural stress characteristics and deformation patterns of"longitudinal and transverse support"system consisting of super-long pipe sheds and temporary inverted arches are investigated.This system is specifically employed in high-speed railway tunnels that cross operational railways in cohesive loess strata.First,a detailed modeling of the super-long pipe shed is conducted using solid elements to analyze the deformation of the strata and stress distribution in the pipe shed.Next,real-time monitoring of the longitudinal stress in the pipe shed is performed using grating optical fiber test technology to reveal the influence range of tunnel excavation on the longitudinal stress of the super-long pipe shed.Finally,the mechanism of the"longitudinal and transverse support"system is analyzed.The results are summarized as follows:(1)A well-integrated super-long pipe shed transfers vertical stress over a large longitudinal range to reduce stress on the steel frame near the tunnel face.(2)The temporary arch forms a closed-loop structure with the supporting structure after excavation,which enhances the overall load-bearing capacity of the steel frame and effectively controls the deformation of the loess tunnel.(3)The minimum distance between the pipe sheds in the longitudinal and transverse support system formed by pipe sheds and supporting structures should be greater than twice the closing distance between the tunnel face and the supporting structure.(4)The influence range of tunnel excavation on the longitudinal stress of the super-long pipe shed is between 30 m in front of the tunnel face and 20 m behind it.The strongly affected range is from 10 m in front of the tunnel face to 5 m behind it.Moreover,the longer the length of the pipe shed,the better its load-bearing effect.