Search Results (55)

Deep excavations in soft ground commonly use permanent foundation piles and temporary support columns as independent systems, causing duplicated construction and discontinuous force transfer. This study proposes an integrated pile–column system in which prestressed high-strength concrete (PHC) pipe piles serve as both permanent foundation piles and temporary excavation support columns. The main scientific contribution is a constructible load-transfer framework for this dual-purpose use. Two steel transition details were developed: a steel sleeve connecting the PHC pile to the steel transfer beam, and a steel transfer structure connecting the pile to the base slab. Together, they establish a continuous column–beam–strut load path. Local three-dimensional finite element models were developed in Abaqus to quantify stress transfer in the critical connection regions under prescribed service-stage actions. The maximum sleeve shear stress and beam axial stress were 27.92 and 112.56 MPa, respectively. The corresponding gross-section elastic bending stress in the PHC pile was 7.48 MPa. The models characterize local connection responses; staged excavation and soil–structure interaction were outside their scope. The system was implemented in the Dongcun Road No. 2021G68 project in Nanjing. Third-party monitoring recorded maximum retaining-wall head displacement, deep horizontal displacement, pile column settlement, and strut force of 10.24 mm, 12.59 mm, 0.43 mm, and 658 kN, respectively. All values remained below the project alarm thresholds. The study establishes a field-documented design framework for PHC pile–column integration and identifies the critical connection regions governing local stress transfer. Full article

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. Full article

Prefabricated pile-cap joints have been applied in concrete pile foundations in waterway revetment structures for decades. However, the mechanical performance of such joints for small-section (≤400 mm) prestressed piles has not been systematically validated, which hinders their application in civil and waterway engineering. This study evaluates this joint system through full-scale tests on six identical 400 mm × 400 mm prestressed concrete pile-cap specimens (C60 pile, C30 joint concrete, HRB400 anchoring bars threaded into embedded steel sleeves) under monotonic tension, bending, and shear, with strain gauges monitoring the response. The results show that the joint sustained a tensile load of 1400 kN, which exceeds the pile’s design value by 52%, a bending moment of 277 kN·m, which is 32% higher than the pile’s ultimate capacity, and a shear force of 680 kN, which reaches more than 2.5 times the design shear, without any occurrence of joint failure. These findings provide the first comprehensive experimental evidence that this prefabricated joint system can effectively transfer tensile, bending, and shear loads in small-section prestressed piles, thereby supporting its safe application in green, industrialized engineering. Full article

Prestressed concrete hybrid-reinforced solid square (PCHSS) piles combine strands and rebars for improved ductility. This study presents large-scale shaking table tests (1:2 scale) on PCHSS pile–superstructure systems embedded in soft and stiff clay, subjected to four ground motions with distinct frequency contents. The experimental program systematically captured the evolution of natural frequencies, damping ratios, dynamic earth pressure distributions, bending moment profiles, curvature ductility demands, and post-test cracking patterns. Results reveal that ground stiffness governs the degradation pathway and energy dissipation mode: soft clay exhibited 37.3% frequency degradation (1.33× that in stiff clay), while stiff clay showed a 101% damping increase (>3× soft clay). Long-period ground motions generated maximum curvature ductility demands and peak bending moments 2–3 times those of short-period records under identical PGA, attributed to near-resonance coupling. Pile–soil interaction transitions from compatible deformation to progressive separation with increasing seismic intensity, with gap spacings of 40–53 mm observed in soft clay. Notably, the code-specified 4D reinforcement zone was found insufficient for soft clay foundations, where crack distributions extended to 4D–7D, warranting an extended zone up to 7D. The findings provide experimental benchmarks for numerical model calibration and offer practical guidance for extending hybrid-reinforced precast piles into moderate-to-high-seismicity regions. Full article

Water leakage in underground construction works is a prominent and persistent quality defect, particularly for the joint between the foundation slab and prestressed anti-floating anchors or piles. Previous studies have focused on optimizing the structural details to improve impermeability, while overlooking water seepage caused by insufficient adhesion at the interface between the polyethylene (PE) sheath and concrete. Therefore, this study aimed to enhance this interfacial adhesion through the hydrophilic modification of PE, thereby improving the impermeability of anti-floating anchors or piles prestressed with retarded-bond tendons. Physical blending modification was adopted in which hydrophilic PE granules were incorporated into ordinary PE. The variations in the water contact angle and mechanical properties of PE were analyzed at contents ranging from 0% to 8%. Adhesion strength tests were conducted to evaluate the changes in the interfacial adhesion strength between ordinary PE, modified PE, and concrete with different cement grades. Water impermeability tests were performed to measure the impermeability grades of concrete specimens reinforced with unbonded, ordinary retarded-bond, and modified retarded-bond prestressing tendons. The results showed that with increasing hydrophilic PE granule content, the hydrophilicity of PE improved markedly, while its mechanical properties improved slightly. A content of 8% hydrophilic PE granules is recommended. Debonding occurs between ordinary PE and concrete, whereas the adhesion strength of hydrophilic PE to concrete gradually increases with the cement grade. The impermeability grade of concrete with modified retarded-bond prestressing tendons is six grades higher than that with ordinary retarded-bond prestressing tendons, reaching P8. This indicates that the incorporation of hydrophilic PE granules significantly improves the impermeability of anti-floating anchors or piles prestressed with retarded-bond tendons. Full article

To investigate the stress evolution, deformation behavior, and failure characteristics of composite-reinforced prestressed concrete hollow square piles (PHSC piles) under bending, a four-point bending test was conducted on a full-scale PHSC500 (340) hollow square pile specimen with a length of 7000 mm, a square section of 500 mm × 500 mm, and a hollow core diameter of 340 mm. The test was used to obtain load–deflection curves, crack propagation patterns, deformation responses, sectional strain distributions, and failure modes. In addition, an ABAQUS finite element model was established to compare the bearing capacity, stiffness degradation, and ductility of different pile types with varying prestressed and non-prestressed reinforcement ratios. The results show that vertical cracks changed their propagation direction at the edge of the tensile zone in the flexural–shear region of the PHSC piles and developed into a critical diagonal crack with a width of 1.7 mm. The specimen ultimately exhibited a shear–compression failure mode. During the failure stage, the midspan deflection increased rapidly as the load rose from 710 to 740 kN, with the deflection increasing from 24.88 to 32.00 mm. The load–midspan deflection curve obtained from the finite element analysis was generally consistent with the experimental results. Moreover, the predicted damage concentration zones corresponded well to the experimentally observed crack locations, indicating that the model can be used to analyze relative variations under different parameter conditions. The combination of prestressed and non-prestressed reinforcement improved the flexural capacity and ductility of the PHSC piles. However, ductility did not increase monotonically with the prestressed reinforcement ratio. These findings provide a reference for evaluating the flexural performance of PHSC hollow square piles and optimizing their reinforcement parameters. Full article

Prestressed centrifugal concrete hollow square piles often require on-site splicing, and the structural reliability of the pile connection largely governs the performance of the assembled pile. To address the limitations of conventional welded and mechanical joints, a section steel plug-in composite joint combining central grouted steel tube anchorage and peripheral end-plate welding was developed and experimentally evaluated. Flexural and shear tests were conducted on 12 full-scale specimens, including pile shaft specimens and joint specimens with cross-sectional side lengths of 400, 500, and 600 mm. The flexural and shear behavior of the jointed specimens was assessed in terms of bearing capacity, load–deflection response, crack development, and failure mode by comparison with the corresponding pile shafts. Under flexural loading, the pile shaft specimens mainly failed by fracture of prestressing steel bars at midspan, whereas the joint specimens failed near the loading point by prestressing steel fracture, indicating that the critical failure region shifted away from the joint core. The flexural capacities of the joint specimens reached about 92–97% of those of the corresponding pile shafts. Under shear loading, both pile shaft and joint specimens mainly exhibited diagonal compression failure in the flexural–shear region, while no obvious damage was observed in the joint core region. The shear capacities of the joint specimens were about 103–130% of those of the corresponding pile shafts. These results indicate that the proposed section steel plug-in composite joint can effectively maintain flexural resistance while enhancing shear performance. The central steel tube, hardened grout, anchorage reinforcement, and peripheral welds jointly contributed to the integrity and force transfer capacity of the connection, showing favorable potential for engineering application in prestressed centrifugal concrete hollow square pile splicing. Full article

This study proposes a work-based interpretation procedure, hereafter referred to as the IDEA method, for identifying the failure-related transition load in monotonic static load tests of pre-stressed high-strength concrete pipe piles. The method was examined using nine full-scale axial compression tests from a site in the lower reaches of the Yangtze River, China. Cumulative work was reconstructed from the measured load settlement curves, and an incremental work response indicator was fitted with a one-break continuous segmented-regression model. The breakpoint was taken as the IDEA estimate, while bootstrap confidence intervals and delta BIC were used to evaluate numerical stability and model support. For the present nine piles, IDEA showed close agreement with the code-interpreted reference loads and yielded the lowest MAPE among the five Q-s interpretation methods considered, whereas the Davisson method showed slightly lower COV and RMSE. Additional perturbation analyses indicated low sensitivity to moderate settlement noise but clear sensitivity to sparse loading records and missing pre-failure points. A preliminary external application to 10 published pile cases showed generally favorable agreement with reference loads reinterpreted from digitized external Q-s curves using a uniform abrupt-settlement criterion. Because the original settlement–time records of the external cases were unavailable, the external assessment is treated as a curve-based transferability check rather than a strictly code-certified validation. Full article

Steel and prestressed concrete traction poles can be fixed to reinforced concrete pile foundations using typical bolted connections. The stainless steel fastening screw is connected to the ordinary steel foundation pile reinforcement by friction welding under specific friction welding process parameters. From the perspective of the structural strength of the connection between the traction pole and the foundation pile, regarding the transfer of tensile and shear forces through a single anchor bolt, the yield strength of stainless steel bolts should be R_e,min ≥ 345 MPa for M30 anchors, R_e,min ≥ 310 MPa for M36 anchors and R_e,min ≥ 300 MPa for M42 anchors. This requirement is reliably met by martensitic stainless steels, while other stainless steels have yield strengths below the required minimum. What truly determines the foundation pile’s load capacity is not the satisfactory mechanical strength of the stainless steel (here, the parameters are met), but the quality of the friction-welded end connection between the reinforcement and the threaded bars. Incorrect selection of the type of prestressing steel in the analyzed connection can have enormous consequences for foundation pile manufacturers. Annual production of foundation piles amounts to thousands of units, and an incorrect decision made by the pile designer at the design stage can result in significant financial losses and a high risk to human life. This article presents the results of studies on friction-welded connections of M30, M36, and M42 threaded bars made of austenitic 1.4301 (AISI 304) and martensitic 1.4021 (AISI 420) stainless steel with B500SP reinforcement bars. The tests yielded negative results for 1.4021 (AISI 420) steel, despite its yield strength exceeding R_e ≥ 360 MPa. Full article

Compared to traditional single/double-row concrete cast-in-place piles or concrete walls commonly used in foundation pit engineering, pre-tensioned prestressed hollow concrete-filled steel tube piles (referred to as prestressed Steel Cylinder Piles, or prestressed SC piles) demonstrate superior advantages including high bearing capacity, light weight, enhanced stiffness, excellent crack resistance, and cost-effectiveness, indicating a promising future in foundation pit engineering. However, current research has paid limited attention to such piles. Only a few experimental studies have focused on their flexural performance. No studies have presented bearing behavior investigations considering soil–pile interactions and the differences between these kinds of piles and traditional piles. To address this gap, this paper conducts a systematic investigation into the bearing performance of prestressed SC piles. A refined finite element analysis model capable of accurately characterizing pile–soil interactions is developed to analyze the mechanical behavior. Subsequently, the elastic foundation beam method recommended by design codes is employed to analyze the internal forces and displacement variations of these piles during excavation. Finally, the predictions by the design code are compared against those from the refined model. Results shows that the established finite element model presents reasonable predictions on monitoring data and experimental results, with deviations in bending moments and deformations within the range of 10–15%; a comparative analysis of different pile types reveals that prestressed SC piles exhibit smaller horizontal displacements and higher bearing capacities; the bending moments and deformations predicted by design methods (elastic foundation beam method) are conservative, with the predicted values significantly higher than those predicted by the refined model. Full article

Reinforced composite prestressed concrete hollow square (RCPHS) piles, installed through pre-drilling, grouting, and static jacking, integrate the large lateral contact area of cement–soil casings with the high strength and stiffness of prestressed concrete cores. This study combines full-scale vertical static load tests and finite-element (FE) simulations to explore the interaction among the core pile, plain-concrete casing, and surrounding soil. Results show that, at 3600 kN, RCPHS piles exhibit 76% less pile-head settlement compared to PHS piles, and a 36.5% reduction in pile-material expenditure is achieved using the RCPHS scheme. At the same settlement of 23 mm, RCPHS piles carry 87% more load than PHS piles. A 3D FE model developed in ABAQUS reveals that the core pile carries approximately 94% of the applied load. When the load exceeds 4180 kN, the axial force in the casing sharply increases at depths of 7–10 m. The simulated P–s curves align well with field measurements, confirming model accuracy. The superior performance of RCPHS piles is attributed to the graded elastic modulus and coordinated stress distribution of the core–casing–soil system, which enhances interface friction and overall load capacity. These findings provide a foundation for the design optimization of RCPHS piles in dense sandy foundations. Full article

This paper addresses the critical challenge of selecting suitable pile foundations in port engineering by systematically investigating the axial bearing behavior of large-diameter steel pipe piles and prestressed high-strength concrete (PHC) piles. The study integrates both numerical simulations and field tests within the context of the Yancheng Dafeng Port Security Facilities Project. A self-balanced static load numerical model for PHC piles was developed using Plaxis 3D, enabling the simulation of load-displacement responses, axial force transfer, and side resistance distribution. The accuracy of the model was verified through a comparison with field static load test data. With the verified model parameters, the internal force distribution of steel pipe piles was analysed by modifying material properties and adjusting boundary conditions. A comparative analysis of the two pile types was conducted under identical working conditions. The results reveal that the ultimate bearing capacities of the 1# steel pipe pile and the 2# PHC pile are 6734 kN and 6788 kN, respectively. Despite the PHC pile having a 20% larger diameter, its ultimate bearing capacity is comparable to that of the steel pipe pile, suggesting a more efficient utilisation of material strength in the latter. Further numerical simulations indicate that, under the same working conditions, the ultimate bearing capacity of the steel pipe pile exceeds that of the PHC pile by 18.43%. Additionally, the axial force distribution along the steel pipe pile shaft is more uniform, and side resistance is mobilised more effectively. The reduction in side resistance caused by construction disturbances, combined with the slenderness ratio (L/D = 41.7) of the PHC pile, results in 33.87% of the pile’s total bearing capacity being attributed to tip resistance. The findings of this study provide crucial insights into the selection of optimal pile types for terminal foundations, considering factors such as bearing capacity, environmental conditions, and economic viability. Full article

Karst geology creates a complex environment with diverse landforms, blurred boundaries, and multi-factor interactions. This paper presents a new drilling pile installation method: drill to a set depth, clean the hole, insert prefabricated piles, and drive or vibrate them to the target elevation. It suits tough geological conditions well. Pile foundations bear both axial and lateral eccentric loads. To explore prestressed high-strength concrete (PHC) pile foundations under eccentric vertical loads in karst areas, on-site bearing capacity tests were conducted. The results show that as load eccentricity increases, PHC pile foundation-bearing capacity drops notably. A finite element model was developed to analyze the stress and strain behavior of PHC pile foundations under eccentric loading in complex geological conditions, aiming to assess their bearing capacity and stability. Key findings include: (1) Under constant external load, the maximum displacement of the PHC pile foundation increases with greater load eccentricity. (2) Enhanced concrete strength reduces the maximum displacement of the pile foundation, while the peak stress remains stable. (3) The height of karst caves has a minimal impact on the bearing capacity and deformation of PHC pile foundations. These results highlight the importance of considering load eccentricity, concrete strength, and cave height in optimizing the design of PHC pile foundations for safety in complex geological settings. Full article

Pile splicing is generally considered in construction because of transportation limits, length requirements, construction means and methods, and strength capacity. A major challenge in the use of precast prestressed UHPC piles is the lack of efficient and effective splicing solutions. To address the problem, this study evaluated different pile splicing methods for UHPC H-piles and their constructability. The analysis and design for strength capacity and detailing presented here are based on relevant established guidelines and design codes for UHPC. This study assessed two pile splicing methods: epoxy-bonded dowels and near-surface mounted bars (NSMBs). The analysis demonstrated that the epoxy-bonded dowel method provides a moment capacity that is 127% of the pile moment capacity in the strong direction and 139% of the pile moment capacity in the weak direction. In comparison, the NSMB method achieved 121% in the strong direction and 106% in the weak direction. Both methods developed the established strength capacity requirements. The constructability of both pile splicing options was evaluated to provide practical guidelines for their preparation in preplanned and unplanned situations. The results reported are for 18-inch UHPC H-piles; however, the construction and analytical approach applies to other pile sizes as well. The pile splicing options developed are recommended for further experimental investigations. Full article

To ensure the connection performance of precast concrete square piles, a screw clamping and welding joint connection is applied to the solid square piles. By conducting full-scale bending performance tests on six solid square pile specimens with cross-sectional side lengths of 300, 450, and 600 mm, including pile bodies, screw clamping joints, screw clamping, and welding joints, the bending load-bearing capacity, deformation capacity, and failure characteristics of the screw clamping–welding joint connection are compared and studied. The results show that the bending failure mode of the pile body specimens is shear failure in the flexural shear section and concrete crushing in the compression zone of the pure bending section; the bending failure mode of the screw clamping joint specimens are the pull-out of steel bar heads at the joint end plate; the bending failure mode of the screw clamping and welding joint specimens are concrete crushing in the compression zone of the pure bending section, steel bar breakage in the tension zone of the flexural shear section, and pull-out of steel bar heads at the end plate. It is worth noting that no significant damage occurred at the joints. The cracks in the pure bending section of the bending specimens mainly develop vertically and are evenly distributed, while some cracks in the flexural shear section develop obliquely towards the loading point, with branching. Compared to the pile body specimens, the cracking moment of the joint specimens is up to 16% higher, the ultimate moment is within 15% lower, and the maximum mid-span deflection is within 25% lower, indicating that the provision of anchorage reinforcement can increase the stiffness and cracking moment of the specimens. Full article