基于强度折减法的隧道洞口段地震稳定性研究
Study on Seismic Stability of a Tunnel Portal Section based onthe Strength Reduction Method

近年来，强度折减法在岩土工程静、动力稳定性分析领域快速发展。基于该方法，相关学者研究了边坡和隧道的动力稳定安全系数。隧道洞口段是围岩、边坡和衬砌结构相互作用的三维复杂结构体，当前对其地震稳定性研究多集中于定性描述，尚不能给出量化的指标。依托振动台试验，建立相应的洞口段三维数值模型，采用强度折减法，引入结合突变理论的塑性区应变能和其他判据，获得洞口段的动力稳定安全系数。结果表明：结合突变理论的塑性区应变能和其他判据得到的安全系数的最大相对误差较小，在洞口段的地震稳定性分析中采用该判据具有简便、量化等优势；计算出的洞口段的动力安全系数与动力加载降低结构稳定性的一般规律相一致；安全系数为1.52说明洞口段有较高的地震稳定性，与振动台试验的实验现象符合。
Recently, the strength reduction method (SRM) has gained importance in static and dynamic fields of Geotechnical Engineering. Based on this method, the dynamic safety factor of slopes and tunnels has been studied by scholars. As a complicated 3-dimensional structure, the tunnel portal section is partly influenced by the interaction between the surrounding rock, slope, and lining of the structure. Seismic stability research is now mostly conducted for qualitative descriptions. To evaluate the dynamic stability of such projects and provide references for design and construction, quantitative indexes should be developed. According to the shaking table test, a numerical model of a 3-dimensional tunnel portal section is built, in which the SRM is adopted to acquire a dynamic safety factor of this section. In this study, the plastic energy criteria (PEC) combined with the catastrophe theory (CT) is used as the failure judgment of the model in deciding the safety factor. Using the CT, the critical changing point of the reduction factor-plastic energy curve is decided. The safety factor of the model then becomes the reduction factor at this critical point. Results show that the PEC combined with the CT have a small error and exhibit the advantages of simplicity and convenience compared with other failure criterion such as displacement criterion, non-convergence criterion and the criterion of plastic zone connection. The dynamic safety factor of the model is smaller than the static safety factor, which is in accordance with the law that structures exhibit lower stability under dynamic loading. The dynamic safety factor is 1.52 for the model, indicating that the portal section in simulating is rather stable, which agrees with the shaking table test results. The results show that the PEC combined with the CT is feasible in such engineering cases, which could provide reference for similar projects.