Search Results (35)

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

With the rapid development of the national economy, the construction of super high-rise buildings, long-span bridges, high-speed railways, and transmission towers has become increasingly common. It is also more frequent to build structures on karst foundations, which imposes higher demands on foundation engineering, especially pile foundations. To study the influence of the roughness factor (RF) on the bearing characteristics of rock-socketed pile, model pile load tests were conducted with different RF values (0.0, 0.1, 0.2, and 0.3) to reveal the failure modes of the test pile, analyze the characteristics of the load–displacement curves and the axial force and resistance exertion law of the pile, and discuss the influence of the RF on the ultimate bearing capacity of the test pile. Based on the load transfer law of test piles, a load transfer model considering the relative pile–soil displacement and the shear dilatancy effect of pile–rock is established to analyze its load transfer characteristics. The results show that the failure mode of the test pile is splitting failure. The load–displacement curves are upward concave and slowly varying. The pile side resistance and the pile tip resistance mainly bear the load on the pile top. As the load on the pile top increases, the pile tip resistance gradually comes into play, and when the ultimate load is reached, the pile tip resistance bears 72.12% to 79.22% of the upper load. The pile side resistance is mainly borne by the rock-socketed section, and the pile side resistance increases sharply after entering the rock layer, but it decreases slightly with increasing depth, and the peak point is located in the range of 1.25D below the soil–rock interface. Increasing the roughness of the pile can greatly improve the ultimate bearing capacity. In this study, the ultimate bearing capacity of the test pile shows a trend of increasing and then decreasing with the gradual increase in RF from 0.0 to 0.3, and the optimal RF is 0.2. The load transfer model of pile–soil relative displacement and pile–rock shear dilatancy effect, as well as the pile tip load calculation model, were established. The calculation results were compared with the test results and engineering measured data, respectively, and they are in good agreement. Full article

In situ vertical load field tests were carried out on two bored piles used in the Chizhou Highway Bridge across the Yangtze River, both of which were rooted piles. Based on the test results, such as those on the relationship between the load and settlement, axial force distribution, and the relationship between shaft friction and pile–soil relative displacement, the vertical load transfer mechanics of the rooted piles were analyzed. The results showed that the load-carrying curves of the rooted piles vary gradually and also that the rooted piles exhibit the bearing characteristics of friction piles because the loads at the pile tips are less than 15% of the total bearing capacity of the piles. The slope of the axial force distribution curve of the rooted piles first increased at the upper interface and then decreased at the lower interface of the root-reinforced zone. The axial force of the rooted piles decreased faster in soil layers where the piles had roots, which can be explained by the fact that roots share the vertical load with piles and that roots improve the bearing properties of piles. Considering the shaft and end resistance of the roots on the piles, the relationship between load and settlement of the rooted piles was calculated by a three-line model based on the load transfer method. The results calculated from the model were in good agreement with the results from the tests. The results from the tests could inform the design and analysis of rooted piles. Full article

The use of screw piles has grown rapidly, yet their varied configurations and behavior in different soils remain key research areas. This study examines the performance of Toe-wing (Tsubasa) and Spiral screw piles with similar tip areas under similar ground conditions, focusing on how the helix position (W_p) and tip embedment depth (E_d) affect the ultimate pile capacity. In the case of a fixed helix/toe-wing position with increasing pile tip depth, Spiral screw piles exhibited higher load-carrying resistance than toe-wing piles at relative densities of 55%, 80%, and 90% fine sand. Moreover, load-carrying resistance increased as the position of the helix/toe-wing increased (W_p > 0). For a fixed pile tip depth (E_d) and varying helix/toe-wing positions, spiral screw piles showed higher resistance than toe-wing piles when W_p < 90 mm. Moreover, the resistance decreased as the helix moved away (W_p/D_h > 0), and the pile tip acted independently when W_p/D_h > 1.38. Whereas, for toe-wing piles, ultimate pile capacity increased as the toe-wing moved away from the tip up to W_p/D_h = 2.15, then decreased to reflect the independent behavior of the toe-wing and pile tip. Empirical equations are presented to convert installation effort and ultimate capacity from one type to another. Full article

Utilizing the results of static load tests using the self-balancing method on two large-diameter bored piles from the Huaiyang Left Line Special Bridge Project of the Lianyungang–Zhenjiang Railway, this study aims to investigate the effect of combined tip-and-side post-grouting on the bearing characteristics of post-grouted piles in railway bridges. The difference in bearing performance between individual piles before and after grouting was evaluated using a comparative analysis. The results show that the bearing capacity of the pile foundations is greatly increased by combined tip-and-side post-grouting. In particular, following grouting, a single pile’s maximum bearing capacity rises from 32.99% to 38.42%. The combined post-grouting produces a compressed grout that enhances the mechanical characteristics of the pile–soil contact, resulting in a significant increase in side resistance all the way along the pile. The combined post-grouting also optimizes the performance of the tip resistance, resulting in a more rapid response as the pile tip displacement increases. Additionally, the combined post-grouting modifies the pile shaft’s load transfer mechanism by increasing the tip resistance’s contribution to the pile foundation’s ultimate bearing capacity and moving the bearing’s center of gravity closer to the pile end. Full article

The presence of isolated stones in the soil layers of engineering sites has significantly increased. Currently, the existing methods for dealing with isolated stones are inadequate to meet engineering needs. This paper combines pile-planting technology with isolated stones to incorporate them into the load-bearing system, resulting in a new type of pre-drilled composite pile suitable for isolated stone sites. A visualization testing system for pile-soil deformation is developed using Particle Image Velocimetry (PIV) technology and transparent soil, conducting non-intrusive model tests on pile-planting and boulder-capped piles under different uplift load conditions, and comparing the results with a discrete-continuous coupled three-dimensional numerical model analysis. The results indicate that when an isolated stone with a cross-sectional area four times that of the pile exists at the pile tip, the ultimate pullout bearing capacity of the pile increases by a factor of two. Regarding the distribution of internal and external side friction resistances of the core and outer concrete of the piles, the internal friction resistance of piles without isolated stones is approximately 1.47 times that of the external friction resistance and about 0.8 times the ratio of the diameters of the pile and core. For piles with isolated stones at the tip, the internal friction resistance is approximately 1.37 times that of the external friction resistance. Under the ultimate load, the displacement field around the pile without an isolated stone exhibits an “inverted triangular” distribution; the displacement field around the pile with an isolated stone at the tip exhibits a “trapezoidal” distribution. This study investigates the bearing capacity and load transfer mechanisms of the new pre-drilled composite piles in isolated stone engineering sites, and the research findings may provide new solutions for similar construction projects involving rubble reclamation. Full article

This study covers the structural optimization of vertical axis wind turbines (VAWTs) that can operate reliably for long periods of time in marine environments, as well as simulation analysis to evaluate their fatigue and strain resistance. Due to the nature of the marine environment, strong wind speeds and constant wave loads are applied, and VAWTs are likely to suffer from fatigue build-up and deformation problems in the long term. In this study, detailed numerical simulations were performed using ANSYS software (2024 R2) to analyze the effects of different airfoil shapes, material choices, tip speed ratios (TSRs), and foundation types on the turbine’s stress distribution and fatigue resistance. The results showed that NACA 0030 airfoil, composite steel, and single-pile foundation performed best under TSR 1.8 conditions, with the potential to reduce strain by approximately 30% and fatigue damage by approximately 25% compared to conventional structures. With this optimized combination, it was found that maintenance costs could be significantly reduced while maintaining structural stability at sea. These results could make an important contribution to the economical and durable design of VAWTs in the future. Full article

In collapsible loess sites, large-scale collapsible settlement may occur after water immersion, which will reduce the bearing capacity of existing highway bridge pile foundations and pose serious potential safety hazards. Given this, a large-scale field pile foundation immersion–loading test was conducted in a collapsible loess site. The settlement law of collapsible loess during the immersion was obtained, the bearing characteristics of pile foundations under the loading and immersion–loading conditions were compared and analyzed, and the formation mechanism of negative skin friction was discussed. The results show that the degree of collapsible deformation is related to the duration of immersion, external load, boundary conditions, and soil layer depth. Whether the collapsible loess site is immersed or not can only change the value and transfer rate of the axial force of the pile foundation but cannot change its transfer law. The collapsible deformation will increase the utilization rate of the pile tip resistance. During the collapsible settlement process, part of the gravity of the soil around the pile will be transferred to the pile, generating negative skin friction on the pile shaft. On this basis, eight preventive measures for reducing the negative skin friction of pile foundations in collapsible loess sites were proposed. The research findings can serve as a valuable reference for the design and construction of highway bridge pile foundations in collapsible loess areas. Full article

Screw-groove piles, a new type of precast pile, are economically and environmentally friendly and improve the load-bearing performance of piles through a unique screw-groove structure. To reveal the load-transfer characteristics and bearing mechanism of the screw-groove pile, the axial force, load–settlement curve, skin friction, bearing capacity, and response characteristics of the foundation for piles under vertical loading were analyzed. Furthermore, a parameter analysis of the ultimate bearing capacity and material utilization of screw-groove piles was performed using the finite element method. The results demonstrate that the screw-groove pile had an ultimate bearing capacity 1.85 times higher than that of the circular pile, and its material utilization rate was 2.85 times higher. The screw-groove surface end resistance and pile-tip resistance formed a multipoint vertical bearing mode. It efficiently utilized the soil’s shear strength and mobilized a larger volume of surrounding soil to share the load. The screw-groove structure increased the pile–soil interaction surface, thereby increasing the skin friction resistance of the pile. Additionally, increasing the inner radius of the screw groove boosts the pile’s bearing capacity but may reduce material utilization. An optimal screw-groove spacing balances both factors, while excessive groove thickness lowers material use. The pile shows high sensitivity to soil parameters. Full article

By integrating laboratory tests and three-dimensional discrete element methods, this research extensively explores the macroscopic and microscopic mechanisms of static pile penetration in standard sand. Initially, the mesoscopic parameters of standard sand were established via flexible triaxial compression tests, and a three-dimensional discrete element model was created using the particle size magnification technique. The study results confirm the rationality of parameter selection and numerical modeling by comparing penetration resistance and displacement obtained from laboratory model tests and discrete element simulations. Initially, penetration resistance swiftly increases, then stabilizes progressively with increasing depth. The lateral friction resistance grows with penetration depth, especially peaking near the cone tip. Moreover, horizontal stress quickly rises during pile penetration, mainly caused by the pile foundation compressing the adjacent soil particles. Displacement of the foundation particles is primarily focused around the pile side and cone tip, affecting an area roughly twice the pile diameter. Soil particle displacement exhibits a pronounced vertical downward movement, primarily driven by lateral friction. The distribution of force chains among foundation particles indicates that the primary stressed areas are at the pile ends, highlighting stress concentration features. This research offers significant insights into the mechanical behaviors and soil responses during pile foundation penetration. Full article

Optimizing open-end piles is crucial for sustainability as it minimizes material consumption and reduces environmental impact. By improving construction efficiency, less steel is needed, reducing the carbon footprint associated with production and transportation. Improved pile performance also results in more durable structures that require less frequent replacement and maintenance, which in turn saves resources and energy. This paper presents a parametric study on optimal designs for open-ended piles in sand, presenting a novel approach to directly compute optimal pile designs using CPT results. It addresses challenges posed by soil variability and layered conditions, with the optimization model accounting for interdependencies among pile length, diameter, wall thickness and soil properties, including the pile–soil plug system. A mixed-integer optimization model OPEN-Pile was developed, consisting of an objective function for pile mass and CO₂ emissions. The objective function was constrained by a set of design and geotechnical conditions that corresponded to current codes of practice and recommendations. The efficiency of the developed optimization model is illustrated by two case studies. In the case of Blessington sand, the calculation results show that it is more economical and environmentally friendly to increase the pile diameter and pile wall thickness than the pile length. In efficient design, the ratio between diameter and wall thickness is calculated at the upper limit. For the optimum design of piles in Blessington sand, the optimum ratios of pile length to diameter, diameter to wall thickness and length to wall thickness are 5, 50 and 250, respectively. In a layered soil profile, the decision of where to place the pile base depends on the resistance of the cone tip and the thickness of the individual layers. To determine in which layer the pile base should be placed, we need to perform an optimization for the given design data. Full article

This paper presents an analysis of long, large-diameter bored piles’ behavior under static and dynamic load tests for a megaproject located in El Alamein, on the northern shoreline of Egypt. Site investigations depict an abundance of limestone fragments and weak argillaceous limestone interlaid with gravelly, silty sands and silty, gravelly clay layers. These layers are classified as intermediate geomaterials, IGMs, and soil layers. The project consists of high-rise buildings founded on long bored piles of 1200 mm and 800 mm in diameter. Forty-four (44) static and dynamic compression load tests were performed in this study. During the pile testing, it was recognized that the pile load–settlement behavior is very conservative. Settlement did not exceed 1.6% of the pile diameter at twice the design load. This indicates that the available design manual does not provide reasonable parameters for IGM layers. The study was performed to investigate the efficiency of different approaches for determining the design load of bored piles in IGMs. These approaches are statistical, predictions from static pile load tests, numerical, and dynamic wave analysis via a case pile wave analysis program, CAPWAP, a method that calculates friction stresses along the pile shaft. The predicted ultimate capacities range from 5.5 to 10.0 times the pile design capacity. Settlement analysis indicates that the large-diameter pile behaves as a friction pile. The dynamic pile load test results were calibrated relative to the static pile load test. The dynamic load test could be used to validate the pile capacity. Settlement from the dynamic load test has been shown to be about 25% higher than that from the static load test. This can be attributed to the possible development of high pore water pressure in cohesive IGMs. The case study analysis and the parametric study indicate that AASHTO LRFD is conservative in estimating skin friction, tip, and load test resistance factors in IGMs. A new load–settlement response equation for 600 mm to 2000 mm diameter piles and new recommendations for resistance factors $\mathsf{\phi }$_qp, $\mathsf{\phi }$_qs, and $\phi$_load were proposed to be 0.65, 0.70, and 0.80, respectively. Full article

The bearing capacity of fiber-reinforced plastic (FRP) helical screw piles is determined by the lesser of the breaking load at the bolted joint and the resistance provided by the screw tip area. In this study, compression and tensile tests were performed with the number of bolts and edge distance as variables. It showed similar strength when compared to the failure stress derived from material testing. In addition, considering load resistance performance, the optimal screw cross section was obtained through parametric analysis. Considering the structural behavior of the screw, a prediction equation was presented to design the screw cross-section as a tapered cross-section using a theoretical method. As a result of comparing the screw cross-section with the finite element analysis results, it was confirmed that the design stress and analysis stress showed an error of 1.1 MPa and were within the allowable stress of 80 MPa. Full article

In recent years, the detection of offshore pile foundations has received wide attention in engineering. Compared with traditional methods, the O-cell test has unique advantages in offshore pile foundation detection. To study the load transfer characteristics of the O-cell method for pile testing in coastal soft soil foundation, this paper established the pile–soil numerical model to simulate the O-cell and traditional testing processes. The finite element method and equal displacement method are combined to calculate the conversion coefficient and ultimate bearing capacity, and the distribution forms of axial force, side friction resistance, and tip resistance are discussed. The research results show that the O-cell test method and the traditional method have different load transfer forms. By introducing the equal displacement method into the O-cell pile–soil model, the error between the equivalent conversion ultimate bearing capacity and the calculation result of the surcharge method is less than 0.5%, and the O-cell conversion coefficient can be accurately calculated. Full article

The mechanical response and deformation characteristics in calcareous sand foundations during pile driving and setup were studied using model tests combined with the technical methods of tactile pressure sensors and close-range photogrammetry. Different types of piles were considered, including a pipe pile, square pile and semi-closed steel pipe pile. The test results show that during pile driving, the pile tip resistance of different piles increases with an increase in the pile insertion depth, and an obvious fluctuation is also obtained due to the particle breakage of the calcareous sand and energy dissipation. Different degrees of particle breakage generated by different type piles make the internal stress variations different, as with the pile tip resistance. The pile tip resistance of model pile A, which simulates a pipe pile, is the highest, followed by model pile B, the simulated square pile. Model pile C, which simulates a semi-closed steel pipe pile, has the smallest pile tip resistance because its particle breakage is the most obvious and the pile tip energy cannot be continuously accumulated. The induced deformation such as sag or uplift on the surface and the associated influence range for the calcareous sand foundation are the smallest for model pile C, followed by model pile B and then model pile A. Model pile A has the most obvious pile driving effect. During the pile setup process after piling, the increase in the total internal stress of model pile B is the largest, and the improvement of the potential bearing capacity is the most obvious, followed by model pile A and model pile C. During the pile setup, the induced uplift deformation in pile driving is recovered and the potential bearing capacity increases due the redistribution and uniformity of the vertical and radial stress distributions in the calcareous sand foundation. Considering the potential bearing capacity of different model piles, the influence range of pile driving, foundation deformation and the pile setup effect, it is suggested to use a pointed square pile corresponding to model pile B in pile engineering in calcareous sand foundations. Full article