Study on Mechanical Behavior of Excavation Supported by Rock-Socketless End-Suspended Piles in Soil–Rock Composite Strata Pit in Jinan

Excavation in soil–rock composite strata poses significant challenges in regard to deformation control due to stiffness contrast and interface discontinuity. Based on the optimization requirements of a foundation pit project in Jinan Metro Line 7, we evaluated an end-suspended pile support system without rock-socket support through physical model tests and numerical simulations. The results indicate that ground settlement exhibits a typical “trough-shaped” distribution with an influence range of approximately 20 m. The pattern of retaining wall displacement evolves from being “inverted-triangular” into a “vase-shaped” during staged excavation, with maximum displacement remaining within code limits. Bending-moment peaks can be observed near strut levels and approximately 1 m above the soil–rock interface, reflecting stress redistribution and differential constraint effects. Parametric analysis demonstrated that increased rock weathering reduces formation stiffness and amplifies deformation and strut forces, whereas moderately weathered rock provides more effective restraint. A steeper interface dip angle induces asymmetric deformation due to stiffness contrast, increasing overall structural demand. An increase in rock-socketed depth, particularly within 4.0–4.5 m, significantly enhances anchorage performance and deformation control. These findings provide quantitative support for optimizing suspended pile systems in soil–rock composite strata.