Yingtao Zhang

To clarify the poorly understood soil-structure interactions flanking the pile cap, this study systematically investigates the sensitivity of the New Type Concrete Expanded-Plate (NT-CEP) pile system to variations in sub-cap silt profiles, specifically moisture content (12%~16%) and dry density (80%~90% compaction degree). Mechanical results indicate that the pile cap and expanded bearing plates operate via a robust synergistic load-sharing mechanism, with plastic failure zones localized beneath these components. Within conventional physical limits, fluctuations in moisture and density trigger less than a 4% variance in the ultimate compressive capacity, demonstrating the remarkable structural resilience of the internal compensatory load-transfer path. Based on the evaluated boundary conditions, a site-specific operational envelope featuring a minimum compaction degree of 80% and a critical moisture threshold below 14% is recommended as a preliminary reference. Nevertheless, explicit mechanical limitations must be rigorously addressed: these quantitative thresholds are strictly benchmarked against the scaled model testing utilizing a specific silt thickness and pile geometric stiffness ratio. Significant deviations in these parameters are expected under three distinct boundary constraints: (1) altered multi-axial stress paths inherent to complex interbedded geologies; (2) catastrophic matric suction loss and pore pressure accumulation driven by elevated groundwater tables; and (3) severe skin friction degradation common in thixotropic soft clays. Consequently, these indicators constitute a context-specific design envelope rather than a rigid universal standard, providing a mechanics-driven baseline for the gradient optimization of advanced NT-CEP foundations while delineating required calibration paths for future full-scale field instrumentation.

Concrete expanded-plate piles (CEP piles) are novel variable-section piles that offer broader applicability, greater bearing capacity, and superior economic benefits compared to conventional straight-shaft piles. Their increasing use in construction projects underscores these advantages. While previous studies have demonstrated the favourable bearing performance of CEP monopiles, the influence of pile spacing on the performance of CEP double piles remains unexplored. This study combines laboratory-scale unitary soil tests with ANSYS Workbench 2022R1 finite element simulations to investigate the effects of pile spacing on the bearing behaviour and soil failure mechanisms of CEP double piles. An optimal pile spacing range is proposed, and the compressive bearing capacity formula is modified accordingly. These findings establish a theoretical foundation for the development of CEP double-pile and pile group foundations, thereby supporting their wider use and promotion in geotechnical engineering.

The NT-CEP pile is an innovative type of pile that builds upon the conventional concrete straight-hole cast-in-place pile. It primarily consists of two components: the main pile and the bearing plate. The key factors influencing its load-bearing capacity include the pile diameter, the cantilever dimensions of the bearing plate, and the slope of the bearing plate’s foot, among others. The pile spacing significantly influences the bearing capacity of NT-CEP pile group foundations. The overall bearing capacity of an NT-CEP pile group foundation is not merely the sum of the ultimate bearing capacities of individual piles; rather, it results from the interactions among the pile bodies, the cap, and the foundation soil. Advancing the design theory of NT-CEP pile groups and enhancing their practical applications in engineering requires an in-depth investigation of how different pile spacings influence the load-bearing performance of pile group foundations. This objective can be achieved by exploring the soil damage mechanisms around side, corner, and central piles. This exploration helps in clarifying the influence of pile spacing on the load-bearing performance. Based on research findings regarding the bearing capacity of single and double pile foundations, this paper utilizes ANSYS finite element simulation analysis to model six-pile and nine-pile groups. Because these arrangements are universally adopted in engineering practice, they are capable of accounting for the pile group effect under various pile spacings and row configurations. The nine-pile group comprises corner piles, side piles, and a center pile, enabling a comprehensive analysis of stress variations among piles at different positions. As six-pile and nine-pile groups represent common pile configurations, studying these two types can provide valuable insights and direct references for optimizing pile foundation design. The study systematically investigates the influence of varying piles spacings on the bearing capacity of NT-CEP pile group foundations. It concludes that, as pile spacing decreases, The displacement of the top of this pile increases. thereby enhancing the group piles effects. Conversely, increasing the spacing between piles represents an effective strategy for elevating the compressive capacity of the NT-CEP pile-group foundation. Larger spacing also increases the vertical load-bearing capacity of the central piles, enhances the lateral friction resistance of corner piles, and heightens the load-sharing proportion between the bearing plate and the pile end. Furthermore, increasing pile spacing raises the ratio of load sharing by the foundation soil for both the CEP nine-pile foundation and the CEP six-pile foundation. The reliability of the simulation study has been verified by a visualization small scale model test of a half cut pile.