Yongmei Qian

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.

Pile‐side friction resistance is an important component of the compressive bearing capacity in new type concrete‐expanded plate (NT‐CEP) piles. Bearing plate position and plate cantilever diameter constitute important factors affecting pile‐side friction resistance. This study employs ANSYS finite element analysis to investigate the specific impacts of bearing plate position and plate cantilever diameter on the effective calculation length of side friction under vertical loading. By systematically analyzing displacement contour and soil stress distribution plots at the ultimate failure state, the results indicate that, as for the plate position, when the distance between the plate and the platform is less than 12 times the pile diameter, the effective calculation length of the lateral friction resistance increases as the plate moves farther away from the platform. However, when this distance is exceeded, the effective calculation length tends to stabilize as the plate moves further away from the platform. In engineering practice, it is recommended that the design value for the pile length above the plate be controlled between 10 and 12 times the pile diameter, with preference given to the smaller value. β ₁ is the influence coefficient between the pile position and the effective calculation length; within this range, its value lies between 0.01 and 0.176. Regarding the plate cantilever diameter, when the cantilever diameter is less than twice the pile diameter, the effective design length decreases as the cantilever diameter increases. Beyond this range, the effective calculated length tends to stabilize. Therefore, in actual engineering practice, the plate cantilever diameter should be kept as close as possible to 1.5–2 times the pile diameter. β ₂ is the influence coefficient between the plate cantilever diameter and the effective calculated length, with values ranging from 0.24 to 1.2 within this range. These findings offer a comprehensive theoretical basis for their future promotion and implementation of NT‐CEP pile systems.

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.

To investigate the local compressive bearing capacity of concrete reinforced with spiral stirrups, a study was conducted on 40 specimens, focusing on the analysis of failure modes and strain variations. The study investigated the effects of concrete strength grade fcg, stirrup diameter d, volumetric ratio of the spiral stirrups ρv, and ratio of core area to load area Acor/Al on the local bearing capacity Fl. The experimental results indicated that the local bearing capacity Fl increased as the ratio of core area to load area Acor/Al decreased, with an observed increase of 23.0%. Furthermore, the local bearing capacity Fl increased with a reduction in stirrup spacing s, showing a 65.4% increase compared to the initial value. An increase in stirrup diameter d also would contribute to a higher Fl, with an improvement of 24.7%. Additionally, the local bearing capacity Fl exhibited a directly proportional relationship with the concrete strength grade fcg. Based on the theoretical analyses, the local bearing capacity of calculation equation Nu′ was established with the reinforcement term ρvfyAl and the concrete term fcAl. The experimental data on concrete reinforced with spiral stirrups were collected to verify the accuracy of calculation equation. The results show that there was a high calculation accuracy for the mechanical model and could provide a reference for local bearing capacity calculation.

The spacing between piles plays a crucial role in determining the load-bearing capacity of CEP group pile foundations equipped with a bearing platform. In this research, five sets of six-pile models with different pile spacings were created using ANSYS finite element analysis. To understand how damage impacts the system, this study examined displacement patterns and stress distribution within both the piles and the adjacent soil. Additionally, the force interaction between the piles and soil was explored to uncover the underlying failure mechanisms. The results shed light on how varying pile spacing affects the overall bearing capacity of the foundations. Based on our thorough analysis, we pinpoint the most effective pile spacing configuration. The findings reveal that, generally speaking, increasing the distance between piles tends to boost the load-bearing capacity of the entire group foundation. However, this relationship is not linear; once the spacing surpasses four times the cantilever’s diameter, further widening does not yield noticeable gains in performance. In real-world scenarios, it is advisable to keep the spacing between 3.5 to 4 times the cantilever diameter for optimal results. Moreover, the stability of the bearing platform and the plate plays a vital role in resisting sideways forces. Ensuring that the shear strength of the surrounding soil aligns with established standards is essential for maintaining the overall durability and safety of the group pile system.

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.

This study investigates the impact of the bearing plate position on the uplift bearing capacity of low-header concrete expanded pile (CEP) foundations using the ANSYS finite element simulation method. Nine models of low-header CEP single piles with varying bearing plate positions are constructed. Incremental loading is applied to obtain relevant data, including load–displacement curves for vertical tensile forces, displacement contours, and shear stress distributions. The study analyzes the characteristics of load–displacement curves under different loading conditions, the axial force distribution along the pile shaft, the failure state of the surrounding soil, and how the uplift bearing capacity varies with changes in the bearing plate position. Based on the findings, a calculation model for the uplift bearing capacity of low-header CEP single-pile foundations is proposed. Given that the uplift bearing capacity decreases to varying degrees depending on the bearing plate position, the slip-line theory from previous studies is applied to refine the corresponding calculation formula for uplift bearing capacity. The results from the ANSYS finite element simulation confirm that the bearing plate position significantly influences the uplift bearing performance of low-header CEP single-pile foundations. The uplift bearing capacity increases with the distance between the bearing plate and the low header, reaching a peak before decreasing beyond a certain threshold. Considering the influence of the bearing plate position on bearing capacity, the affected area of soil beneath the foundation, and the time required for the system to enter its working state, the optimal bearing plate position is found to be at a distance of d₁ = 4R₀ to 5R₀ from the top of the pile.

The compressive bearing capacity of a new type of concrete-expanded plate pile (NT-CEP pile) is significantly affected by the size of the bearing platform; however, research in this area remains limited. Therefore, this study investigates the effect of bearing platform size on the compressive bearing capacity of an NT-CEP pile foundation under combined vertical and horizontal loads. Using ANSYS finite element software, a four-pile model was established to analyze the failure behavior of the bearing platform and surrounding soil under these loads. The findings indicate that in an NT-CEP four-pile foundation, the bearing capacity of piles with a bearing platform increased by 66.67% compared with those without one. However, although the bearing capacity increased with platform size, this increase reduced after reaching a certain threshold. Optimal bearing performance was achieved when the platform size was 1.5 times the pile diameter from the edge to the pile center. High shear stress at the junction between the lower part of the platform and pile body suggested a potential stress concentration. The findings emphasize the importance of maintaining the optimal bearing platform size and reinforcing the connection between the platform and pile body to prevent local damage from affecting the overall bearing capacity.

The disc overhang diameter can significantly affect the uplift bearing capacity of new concrete expanded-plate pile groups, affecting their design and practical applications. Accordingly, this effect was investigated considering the failure laws of the soil surrounding various pile types and groups. Based on the uplift bearing capacities of single and double piles, a finite element simulation was adopted to establish models for the four-, six-, and nine-pile groups. The relationship between the disc overhang diameter and uplift-bearing capacity of each pile group was explored: as the disk overhang diameter increased, the uplift-bearing capacities of the pile groups increased; however, this relationship is nonlinear. The optimal disc overhang diameter was determined as 1.5–1.75 times the pile diameter. For a constant disc overhang diameter, corner piles have a greater uplift bearing capacity than side piles in the six-pile group, and a greater uplift bearing capacity than the side and center piles in the nine-pile group. Thus, the pile-group effect depends on the pile position. The uplift bearing capacity did not increase linearly with the number of piles, and the average uplift bearing capacity of a pile in a pile group was less than that of a single pile. Therefore, the uplift bearing capacity of the pile groups decreased as the number of piles increased. The reliability of the simulation was verified via visual testing of a small-scale half-cut pile model.