To address the difficulty in accurately evaluating the vertical bearing behavior of prestressed high-strength concrete (PHC) pipe pile-group foundations, this study investigated three single piles and an eight-pile group with a Wang-shaped irregular pile cap through field static loading tests and theoretical analysis. The measured ultimate bearing capacities of single piles D1/D2 and D3 were 7040 and 3000 kN, respectively. For the pile-group foundation, the ultimate bearing state was not reached under the maximum applied load of 15,000 kN, at which the settlement was only 3.52 mm. The pile-head load distribution followed the order corner piles > side piles > inner piles, with corresponding load proportions of approximately 13.9%, 12.9%, and 9.4%. The calibrated API and hyperbolic models predicted the single-pile bearing capacities with errors ranging from 0.23% to 3.40%. The API model better represented the steep-drop portion of the Q-s curve, whereas the hyperbolic model more accurately predicted the initial stiffness and low-load response. For pile-group foundations, the combined equivalent-pier and load-transfer method showed good applicability. The main contribution of this study is to provide field evidence for the vertical bearing and load-transfer behavior of a large-diameter PHC pipe pile group with a Wang-shaped irregular pile cap, extending existing studies that have mainly focused on single piles or conventional symmetric pile groups. The results also provide a quantitative basis for the analysis and design of PHC pipe pile-group foundations in highway bridge engineering.

Based on the Su-Tai Expressway Phase I project, this study investigates the lateral bearing characteristics of two PHC800(130)-AB single piles and one Wang-shaped pile group foundation through field lateral loading tests and theoretical calculation. The tests were conducted at the same site and under the same borehole-defined ground conditions, using one pile diameter and one spacing. According to the single-pile lateral test results, the Reese ultimate soil resistance equation was modified, and a hyperbolic tangent backbone function was adopted to establish a p–y curve formulation that can be predicted from geotechnical parameters. The lateral response of the pile group foundation was calculated using the p–y curve reduction method, and finite-difference iterative analyses of laterally loaded piles were performed using LPile. The results show that the API method produced overly conservative results and substantially underpredicted the measured single-pile response at this site. The proposed formulation improved the comparison, but the calculated pile-head displacement still differed from the measured value by approximately 25% at 440 kN. For the Wang-shaped group, the Reese p-multipliers produced conservative predictions, with pile-response errors ranging from −13.3% to −23.8% at approximately 40 mm displacement. The proposed method is computationally efficient and suitable for engineering application. However, the findings are limited to the tested PHC800(130)-AB piles and ground conditions; they provide a site-specific engineering reference and do not establish general validity. Further validation is required for other pile diameters, spacings, group arrangements, or geological conditions.