The pull-pile support structure in a deep foundation pit is a three-dimensional spatial structure system composed of front-row piles

back-pull piles

a crown beam

and tie beams. Existing engineering cases demonstrate that the pull-pile support structure effectively resists overturning and controls horizontal deformation

yet lacks comprehensive theoretical support and systematic research. To thoroughly investigate the deformation behavior

internal force evolution

and working mechanism of the pull-pile support system during foundation pit excavation

an indoor scale test was conducted. Results indicate that the horizontal displacement curve of the front-row pile is convex

the bending moment curve is anti-S shaped

the axial force curve is shuttle-shaped

and the axial force on the pile body is compressive force. The bending moment curve of the back-pull pile is bow-shaped

and the axial force curve is spoon-shaped. The upper section of the back-pull pile experiences axial tension

while the lower section experiences axial compression. The horizontal lateral displacement curve of the crown beam presents sine function shape of the short crown beam

and the axial force curve presents an obvious M shape. The double peaks of the M shape correspond to the crown beam atop the front-row pile without back-pull support

marking a weak point for potential failure of the crown beam. The spatial characteristics of the pull-pile support structure allow for a stable tension-compression combined structure

forming a large triangle with two smaller triangles and a three-way door frame. The resulting back-pull pile effect and spatial deformation coordination can anchor the front-row pile and shield against earth pressure

as well as suppress differences in the top inclination angle of the supporting pile and excessive deformation of crown beam.