管棚力学行为的解析分析与现场测试

Analytical approach and field monitoring for mechanical behaviors of pipe roof reinforcement

管棚超前预支护在隧道上部形成纵向拱效应,从而保证隧道的安全开挖。然而由于模型边界条件的复杂性,目前多局限于从管棚对控制围岩变形和开挖面稳定的整体效果进行研究,无法分析管棚真实的力学行为。对管棚的Winkler弹性地基梁模型进行了改进,并考虑了初期支护的延滞效应,基于Pasternak弹性地基梁理论,推导了管棚的挠度方程和内力计算公式,并提出求解方法。以一隧道开挖为例,通过Pasternak模型和Winkler模型的计算结果与管棚的现场测试数据的对比分析,说明Pasternak模型较Winkler模型与现场测试曲线吻合更好,说明Pasternak模型改进了Winkler模型中地基变形不连续的缺陷,更符合实际受力情况,能较好地反映管棚在隧道开挖过程中的真实力学行为。计算结果表明:管棚起着杠杆作用,能够有效地将开挖面附近的上部荷载向未开挖区传递,从而控制隧道变形,保证开挖面的稳定。

Pipe roof reinforcement allows safe excavation by creating longitudinal arching parallel to the tunnel axis. The complexity of boundary conditions of this method,however,imposes difficulties to understand the reinforcement mechanism. In this study,considering the delay effect of initial lining and revising the Winkler elastic foundation model,an analytical approach based on Pasternak elastic foundation beam theory for pipe roof reinforcement was put forward. With the example of a certain tunnel excavation,the comparison of the results between field monitoring,Winkler model and Pasternak model was made. The results indicate that the Pasternak model,which considering a more realistic hypothesis in the elastic soil than Winkler model,gives more accurate calculation and agrees better with the result of field monitoring,and is proved to be a better way to understand the reinforcement mechanism and improve design practice. The calculation results also reveal that reinforcing pipes act as levers,which increase longitudinal load transfer to an unexcavated area,and consequently decrease deformation and increases face stability.