为研究钢支撑滞后施工对钢支撑轴力、围护桩位移及弯矩、冠梁内力的影响，以某明挖暗埋隧道基坑为工程依托，通过监测数据分析钢支撑滞后施工时围护桩深层水平位移以及钢支撑轴力的变化规律。通过数值模拟得到实际滞后工况、正常施工工况以及单道钢支撑滞后工况下的围护结构内力及变形，同时引入影响系数量化钢支撑滞后施工对围护桩深层水平位移及弯矩、钢支撑轴力、冠梁弯矩及剪力的影响。结果表明： 1）围护桩深层水平位移受第1道钢支撑影响最大，且影响范围大于土方开挖范围，而对围护桩弯矩的影响范围与土方开挖范围一致； 2）冠梁更易受弯破坏而非受剪破坏； 3）钢支撑滞后施工下，邻近钢支撑的轴力可以分担一部分滞后钢支撑的轴力，但同一断面内钢支撑的轴力和仍小于及时支撑工况； 4）位于土方开挖与非开挖交界处的围护桩弯矩、深层水平位移、钢支撑轴力均为临近范围内的最大值。
To study the impact of delayed steel support
construction on the axial force of steel supports, displacements, and bending
moments of retaining piles, and internal force of the crown beam, a case study
is conducted on the foundation pit of an opencut and
buried tunnel. Monitoring data is used to analyze the variation laws of
retaining pile displacement and axial force of steel support during delayed
steel support construction. The internal force and the deformation of the
retaining structure under the actual delayed, normal construction, and delayed
conditions of single steel supports are obtained through a numerical
simulation. Moreover, the influence coefficient is introduced to quantify the
impact of delayed steel support construction on the horizontal displacement and
the bending moment of the deep layer of the retaining pile, the axial force of
the steel support, the bending moment, and shear force of the crown beam. The
results show the following: (1) The horizontal displacement of the deep layer
of the retaining pile is mainly affected by the first steel support, and the
influence range is larger than that of earthwork excavation. In contrast, the
influence range of the bending moment of the retaining pile is consistent with
that of earthwork excavation. (2) The crown beam is more susceptible to bending
than shearing. (3) Under the delayed construction, the axial forces of adjacent
steel supports can share part of the axial forces of the delayed steel support,
whereas the sum of axial forces of steel support in the same section is still
less than that of timely support. (4) The bending moment of retaining pile, the
horizontal displacement of deep layer, and the axial force of the steel support
at the junction of earthwork and trenchless excavations are all in their maximum
in the adjacent range.
