黏弹性条件下大跨度公路黄土隧道二次衬砌施作时机

Construction time of secondary lining of large span loess tunnel under viscoelasticity condition

为研究大跨度公路黄土隧道二次衬砌施作时机,以神府(神木—府谷)高速公路墩梁隧道为依托,采用现场测试、数值模拟和理论分析相结合的方法,首先对隧道拱顶变形进行现场测试,揭示其变形规律,提出了基于隧道二次衬砌安全临界状态的最佳施作时机计算方法;其次根据黏弹性条件下隧道围岩变形理论公式,结合现场监测数据反演分析得到围岩Kelvin模型流变参数;最后利用提出的最佳施作时机计算方法和Kelvin流变模型,通过数值模拟研究了黏弹性条件下大跨度黄土隧道二次衬砌最佳施作时机。结果表明:大跨度公路黄土隧道变形经历急剧变形、持续变形和缓慢变形3个阶段,各阶段产生的沉降值分别为最大沉降值的67.7%,21.7%和10.6%;Kelvin模型中蠕变参数黏性元件黏滞系数η为2.75×10^(14) kPa·s,与黏性元件串联的弹簧元件弹性模量E1为138.3 MPa,与黏性元件并联的弹簧元件弹性模量E2为321.5 MPa;大跨度公路黄土隧道Ⅴ级围岩深埋段二次衬砌最佳支护时机为初期拱顶下沉速率小于0.3 mm/d。

To study the best construction time of secondary lining for large-span loess tunnel, based on the Dunliang Tunnel in Shenfu(Shenmu to Fugu) Highway, the method of field test, numerical simulation and theoretical analysis was used. Firstly, the deformation laws of the tunnel vault settlement were obtained by on-site measurement. Then, the calculation method of optimal construction time based on the safety critical state of secondary lining was proposed. Secondly, according to the theoretical formula of surrounding rock mass deformation under viscoelastic condition, combining with the field monitoring data, the rheological parameters of Kelvin model were obtained. Finally, combined with the calculation method of optimal construction time and Kelvin rheological model proposed in this paper, the optimal construction time of secondary lining of large-span loess tunnel under viscoelastic condition was studied by numerical simulation. The results show that settlement of the vault experienced three deformation stages, rapid deformation stage, sustained deformation stage and slow deformation stage, and the settlement value of each stage was 67.7%, 21.7% and 10.6% of the maximum settlement value, respectively. The viscosity coefficients η of creep parameter viscous element in Kelvin constitutive model is 2.75×10^(14) kPa·s, the elastic modulus E1 of the spring element in parallel with the viscous element is 138.3 MPa, and the elastic modulus E2 of spring element in parallel with viscous element is 321.5 MPa. The best construction time of secondary lining in deep buried section of grade Ⅴ surrounding rock mass of large-span highway loess tunnel is when the vault settlement rate of primary support is less than 0.3 mm/d. 10 tabs, 12 figs, 27 refs.