平顶直墙地铁车站PBA工法施工可以采用管棚先行支护。针对PBA法暗挖平顶直墙地铁车站密布横向管棚结构，通过总结管棚“荷载－梁模型”中弹性地基梁、简支梁、固支梁3种简化方法及其计算原理，以北京地铁19号线平安里站工程为背景，采用上述3种模型计算管棚受力变形，并与实测值进行比较分析，然后针对不同工程参数和地质参数进行受力变形影响分析。结果表明： 1）弹性地基梁模型计算弯矩和跨中挠度处于固支梁模型和简支梁模型计算结果之间，其中弹性地基梁模型和简支梁模型计算结果较符合实测数据；但简支梁模型和固支梁模型无法体现导洞侧壁处挠度，且无法体现地层参数的影响以及钢管壁厚对受力的影响。2）最大弯矩值出现在简支梁的跨中，建议在设计时以简支梁模型计算跨中弯矩进行包络，以保证施工安全。3）开挖跨度和覆土厚度（荷载）对弯矩和挠度影响较大，其中跨度影响最大。4）基床系数和钢管壁厚对管棚弯矩影响较小，但对减小挠度有一定作用。
The pipe roof support can be used in metro station
with rectangular crosssection constructed by PBA method in
advance. The transverse pipe roof is densely arranged in PBA mined metro
station with rectangular crosssection. Firstly, the
simplified methods and calculation mechanisms of elastic foundation beam,
simply supported beam and clamped beam of the "loadbeam model" of pipe roof are summarized. And then, the three
models of elastic foundation beam, simply supported beam and clamped beam are
used to calculate the stress and deformation of pipe roof of Ping′anli Station
on Beijing Metro Line No. 19, and the calculation results are compared with
monitoring results. Finally, the influence factor analysis is carried out on
stress and deformation of pipe roof of different projects with different
geological parameters. The research results show that: (1) The bending moments
and midspan deflections calculated by elastic
foundation beam model are between the results calculated by clamped beam model
and simply supported beam model, and the results calculated by the elastic
foundation beam and the simply supported beam model are more consistent with
the measured data; however, the models of simply or clamped supported beam can
not reflect the deflection at the sidewall and the influence of the formation
parameters and the pipe thickness. (2) The maximum bending moment occurs in the
midspan of simply supported beam, thus the security
can be ensured by using midspan moments of simply
supported beams. (3) The excavation span and soil thickness (load) affect the
bending moment and deflection of pipe roof greatly, and the influence of span
is greater. (4) The foundation bed coefficient and pipe thickness affect the
bending moment of pipe roof little, while they can reduce the deflection to a
certain extent.
