Effect of Steel Support Cross-Section and Preloaded Axial Force on the Stability of Deep Foundation Pits

To investigate the effects of steel support cross-section dimensions and preloaded axial force levels on the stability of foundation pits, numerical simulations were conducted for open-cut deep foundation pits based on monitoring data from Changchun Metro Line 9. Results show that increasing the wall thickness and diameter of the steel support significantly reduces the horizontal displacement and axial force of the enclosure pile. When the wall thickness increases from 14 mm to 25 mm, the horizontal displacement of the enclosure pile can be reduced by up to 7.63 mm, and the axial force of the steel support can be reduced by 11.4–15%. When the diameter of the steel support changes from 609 mm to 800 mm, the axial force of the second steel support is reduced by 3.2–5.5%. The change in preloaded axial force results in a horizontal displacement change of about 3–5 mm and a surface settlement change of about 0.6–4.2 mm. The preloaded axial force meets pit stability control requirements when it reaches 60% of the design axial force.