大跨隧道台阶法转换时机及安全性评价研究

Study on Conversion Time and Safety Evaluation of Bench Method in Long-Span Tunnel

以广东紫惠高速公路项目凤安隧道为研究背景,通过对凤安隧道现场围岩变形监控量测数据和现阶段围岩成拱能力进行分析,研究和探讨了凤安隧道在现有工程地质情况从CD法向台阶法转换的可行性,并确定了工法转换的时机并分析了工法转换的安全系数。此外为讨论一般情况下大跨隧道台阶法的适用性和安全性,利用有限元分析软件对台阶法的转换时机和工法转换安全系数进行了研究。结果表明:在Ⅳ级围岩中,台阶法工法转换宜选择在入岩高度≥12 m时进行,此时工法转换安全系数为1.4;在Ⅲ级围岩中,台阶法工法转换宜选择在入岩高度≥8 m时进行,此时工法转换安全系数为1.5。本文研究成果对类似隧道工程施工具有指导意义。

Taking Feng’an tunnel of Zihui freeway project in Guangdong Province as the background,this paper studies and discusses the feasibility of the transformation from CD method to bench method in Feng’an tunnel under the existing engineering geological conditions by analyzing the on-site monitoring data of surrounding rock deformation and the arching capacity of surrounding rock at the present stage,and determines the time of the transformation and analyzes the safety factor of the transformation.In addition,in order to discuss the applicability and safety of bench method in large-span tunnel,the conversion time and safety factor of bench method are studied by using finite element analysis software.The results show that:in grade IV surrounding rock,bench method conversion should be carried out when the rock entry height is 12 m,and the safety factor is 1.4;in grade III surrounding rock,bench method conversion should be carried out when the rock entry height is 8 m,and the safety factor is 1.5.The research results have guiding significance for similar tunnel construction.