公路隧道应力释放率对软弱围岩稳定性影响

近年来,由于新奥法广泛地运用于地下工程的施工过程中,围岩与支护结构之间的相互作用以及支护时机受到越来越多的关注。中条山隧道洞口段软弱围岩开挖步序多、工序及应力变化复杂,尤其是核心土解除后和二衬施工前安全风险大。本文采用有限差分软件对该隧道洞口段施工过程进行三维数值模拟,研究了洞周位移及支护结构在不同应力释放率下的力学响应,重点分析了典型断面处洞周围岩及支护结构的位移和受力情况,以及洞周位移随施工过程的动态变化规律。研究结果表明：对于软弱围岩公路隧道,应力释放率越大,围岩的塑性区发展范围越大,洞周位移越大;开挖过程中,拱顶沉降受到的持续性扰动较大;待二次衬砌施作后,仰拱隆起和收敛位移趋于稳定。

Effects of Stress Release Rate on Stability of Soft Surrounding Rock in Highway Tunnels

In recent years,NATM is widely used in the construction of underground engineering,the supporting time and the interaction between rock and support structure are increasingly concerned.There are multiple steps in the construction of soft surrounding rock in the portal section of Zhongtiaoshan tunnel,and the construction sequences and the stress variation are complicated.Particularly,high risk exists after removal of core soil and prior to installation of secondary lining.In this paper,the three-dimensional numerical simulation of construction process of portal section of the tunnel has been performed by finite difference program FLAC3D.The displacements of the surrounding rock and mechanical responses of the supporting structure under different stress release rates are studied.Especially,the situations in typical cross sections are investigated in details,and the dynamic variation laws of the displacement of surrounding rock during the construction process are also analyzed.The results show that the plastic zone and displacements of surrounding rock increase with the increase of stress release rate in the tunnel with soft surrounding rock.The settlements of the tunnel vault increase consecutively during the construction process.The heave of tunnel invert and the convergence displacement of waist of the tunnel tend to constant after the construction of secondary lining.