Experimental Study on Lateral Bearing Characteristics of Prestressed High-Strength Concrete Pipe Pile Group Foundations

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.