Abstract: 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 opencut 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.

Key words: open-cut and buried tunnel, influence coefficient, steel support, delayed construction, deep horizontal displacement of piles, bending moment of piles, axial force of steel supports, internal force of crown beam