Mingxing Zhu

Evaluating the lateral bearing behavior of rectangular piles in sloping ground is computationally demanding due to the complex three-dimensional spatial pile-soil interaction. To circumvent the inefficiency of full-scale numerical modeling and the limitations of conventional p-y methods, this study proposes a simplified analytical framework for rapid preliminary design. By systematically isolating the topographical slope effect and the cross-sectional shape effect, a series of mathematical modification factors, namely the ultimate lateral capacity factor K_H, the maximum bending moment factor K_M, and the maximum reverse shear force factor K_Q, were established utilizing a standard level-ground square pile as the computational baseline. The results indicate that increasing the slope angle from 0° to 30° reduces the lateral capacity by approximately 14–20%, whereas increasing the aspect ratio from 1 to 4 effectively compensates for this reduction, improving the capacity by approximately 75%. However, the correspondingly enhanced flexural stiffness simultaneously triggers a substantial non-linear amplification in both the maximum bending moment and the deep reverse shear force. Benchmark comparisons show a maximum deviation of 4.58% for lateral capacity, while the maximum deviations in bending moment and reverse shear force are 10.43% and 9.78%, respectively. By integrating these modification factors with conventional equivalent calculation methods, this study provides an efficient analytical tool for rectangular pile foundation design in sloping ground.

Aiming at the problem that strip surcharge in coastal soft soil foundations causes lateral squeezing and endangers the safety of adjacent existing bridge pile foundations, the traditional Boussinesq elastic theory cannot reflect the true elastoplastic characteristics of the soil and tends to underestimate the actual horizontal additional stress. This paper establishes a two-dimensional plane strain finite element model and, based on the calibration of pure elastic theoretical solutions, carries out extensive comparative analyses under elastoplastic foundation conditions. Through Pearson correlation and random forest sensitivity analyses, it is clarified that the internal friction angle, load ratio, and normalized distance ratio are the core control variables affecting the redistribution of horizontal additional stress, thereby demonstrating the limitations of the influence of elastic modulus and cohesion. The study reveals the nonlinear amplification mechanism of horizontal stress transfer caused by the penetration of the deep plastic zone within the foundation, as well as the physical evolution law of the stress correction factor, which initially exhibits a Gaussian peak enhancement and subsequently decays exponentially with spatial distance. Based on these mechanisms, a combined prediction formula for the horizontal additional stress correction factor is proposed, achieving an R² = 0.903, and a safety evaluation chart for the correction factor is constructed to quantify high-risk areas. The results indicate that when the normalized distance ratio is greater than or equal to 4, the elastoplastic squeezing effect essentially dissipates. The proposed modification method effectively delineates the applicable boundary of the elastic solution and provides a theoretical basis for the bearing capacity calculation and safety control of passively loaded pile foundations in soft soil regions.

Rectangular piles are increasingly utilized in engineering due to their high lateral bearing capacity, which benefits from an adjustable cross-sectional stiffness. However, research on rectangular piles within slope topography remains relatively scarce. Therefore, based on the principle of equal cross-sectional area, this paper establishes four sets of finite element models for rectangular piles with varying aspect ratios to conduct numerical analyses of their bearing characteristics under combined loading at slope angles of 0°, 15°, 20°, and 30°. The results demonstrate that: (1) Under combined loading, the lateral and vertical bearing capacities of rectangular piles interact; as the loading angle increases, the lateral bearing capacity decreases while the vertical bearing capacity increases. (2) Increasing the aspect ratio can significantly enhance the bearing capacity of rectangular piles. Under flat-ground conditions, compared to a pile with an aspect ratio of 1, a rectangular pile with an aspect ratio of 4 exhibits a roughly 75% increase in ultimate lateral bearing capacity and a 15.8% increase in vertical bearing capacity. (3) The critical section of the pile typically occurs within a depth range of 0.28 L to 0.43 L, where its stress mode gradually transitions from predominantly lateral bending and shearing to primarily vertical axial compression. (4) Slopes induce a reduction in the pile’s bearing capacity, but the bearing capacity curve for the pile with an aspect ratio of 4 declines more gently. Thus, rectangular piles with large aspect ratios possess greater engineering applicability in slope topography. This study reveals the bearing mechanism of rectangular piles under the combined influence of the slope weakening effect and the cross-section enhancement effect, providing a methodological reference for the design and application of novel pile foundations in slope terrains.

Pile-anchor foundations, serving as one of the anchoring solutions to ensure the safety and stability of floating offshore wind turbines, are primarily subjected to inclined loading induced by anchor chain forces, resulting in significantly different bearing behavior compared to conventional vertically loaded pile foundations. However, experimental research on the inclined pullout performance of anchor piles remains insufficient. To address this gap, this study employs a self-developed servo-controlled loading system to investigate the pullout bearing characteristics of anchor piles in dry and saturated sand, considering factors such as pullout angle and loading point depth. The research results show that from the load–displacement curve of the model pile, it can be found that with the increase in displacement, the load it bears first gradually increases to the peak, then decreases, and then gradually stabilizes. The loading angle has a significant impact on the bearing performance of pile-anchor foundations. As the loading angle increases, the failure mode shows pullout failure. When the loading angle increases from 30° to 60°, the bearing performance of the pile foundation decreases by approximately 63%. When the depth of the loading point increases from 0.22 times the pile length to 0.78 times the pile length, the diagonal anchor tensile bearing capacity of the model pile increases by approximately 45%. When the depth of the loading point is the same, the distribution patterns of bending moment and shear force are basically similar. However, the smaller the loading angle, the larger the value. This is because the horizontal load component plays a dominant role. The compression of the piles above and below the loading point, as well as the bending moment, shear force and axial force under saturated sand conditions, are similar to those in dry sand, but their values are reduced by about 50%. It can be seen that the soil conditions have an influence on the bearing characteristics of pile foundations.

Suction caisson anchor foundations have been widely applied in oil and gas platforms but remain in the exploratory stage for floating offshore wind power applications, where research on their anchor load-bearing characteristics is insufficient. This study focuses on the influence of length-to-diameter ratio, loading angle, and loading point depth on the anchor load-bearing characteristics of suction caisson anchor foundations. Through numerical simulation, the load–displacement curves, internal force distribution along the caisson body, movement mode transitions, and soil failure characteristics were obtained. The results indicate that loading point depth and loading angle alter the movement mode of the suction caisson anchor foundation, directly affecting its bearing capacity. Smaller loading angles result in higher bearing capacity, which initially increases with loading point depth, peaks at 0.6 L, and then decreases at 0.8 L due to a transition in the foundation’s movement mode. Similarly, as the length-to-diameter ratio decreases, the bearing capacity and overall movement amplitude of the foundation decrease, leading to a shift in the optimal loading point position. The circumferential soil pressure and horizontal soil resistance distributions vary significantly with loading angle and depth. The findings of this study provide valuable reference for the design and application of suction caisson anchor foundations.

As one of the mooring foundation types for floating wind turbine platforms, research on the anchor pullout bearing characteristics of mooring pile foundations remains insufficient, and the underlying mechanism of anchor pullout bearing capacity needs further investigation and clarification. This paper conducts a numerical study on the bearing characteristics of mooring pile foundations under tensile anchoring forces with loading angles ranging from 0° to 90° and loading point depths of 0.2L, 0.4L, 0.6L, and 0.8L (where L is the pile length). The research findings indicate that the anchor pullout bearing capacity decreases as the loading angle increases from 0° to 90°, and exhibits a trend of first increasing and then decreasing with the increase in loading point depth. For rigid pile-anchors, the maximum anchor pullout bearing capacity occurs at a loading point depth of 0.6–0.8L, while for flexible piles, it appears at 0.4–0.6L. Both the bending moment and shear force of the pile shaft show abrupt changes at the loading point, where their maximum values also occur. This implies that the structural design at the loading point of the mooring pile foundation requires reinforcement. Meanwhile, the bending moment and shear force of the pile shaft gradually decrease with the increase in the loading angle, which is attributed to the gradual reduction of the horizontal load component. The axial force of the pile shaft also undergoes an abrupt change at the loading point, presenting characteristics where the upper section of the pile is under compression, the lower section is in tension, and both the pile top and pile tip are subjected to zero axial force. The depth of the loading point significantly influences the movement mode of the pile shaft. Shallow loading (0.2–0.4L) induces clockwise rotation, and the soil pressure around the pile is concentrated in the counterclockwise direction (90–270°). In the case of deep loading, counterclockwise rotation or pure translation of the pile shaft results in a more uniform stress distribution in the surrounding foundation soil, with the maximum soil pressure concentrated near the loading point.

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.

Piles in marine environments are subjected to various loads of differing magnitudes and directions, and their long-term stability has attracted much attention. Most research focuses on lateral cyclic loading; there are few full-scale tests that consider the effects of cyclic loading at different inclined angles. A long-term inclined cyclic loading strategy was used to carry out laboratory tests to study different inclined angles on the pile. The results show that a smaller inclined angle (θ_L) or a larger pile–soil relative stiffness (T/L) results in wider and deeper sediment subsidence after 10,000 cycles. As θ_L increases from 0° to 80°, the peak displacement at the pile head during the first load decreases, while the accumulated displacement initially decreases and then increases. For slender piles, the normalized inclined cyclic loading stiffness (k_lN/k_l1) and unloading stiffness (k_uN/k_u1) first decrease and then increase. For semi-rigid piles, both k_lN/k_l1 and k_uN/k_u1 gradually decrease. On the other hand, as θ_L increases, k_lN/k_l1 and k_uN/k_u1 increased more sharply in the initial stage, with a quicker transition from rapid growth to stability. At θ_L = 80°, peak values are reached early during the initial loading phase. Based on this, prediction formulas for inclined cyclic cumulative displacement, loading stiffness, and unloading stiffness were established and verified.

Concrete-filled FRP (Fiber Reinforced Polymer) tube composite piles offer superior corrosion resistance, making them a promising alternative to traditional piles in marine environments. However, their performance under cyclic lateral loads, such as those induced by waves and currents, requires further investigation. This study conducted model tests on 11 FRP composite piles embedded in sand to evaluate their behavior under cyclic lateral loading. Key parameters, including loading frequency, cycle count, loading mode, and embedment depth, were systematically analyzed. The results revealed that cyclic loading induces cumulative plastic deformation in the surrounding soil, leading to a progressive reduction in the lateral stiffness of the pile–soil system and redistribution of lateral loads among piles. Higher loading frequencies enhanced soil densification and temporarily improved bearing capacity, while increased cycle counts caused soil degradation and reduced ultimate capacity—evidenced by an 8.4% decrease (from 1.19 kN to 1.09 kN) after 700 cycles under a 13 s period, with degradation rates spanning 8.4–11.2% across frequencies. Deeper embedment depths significantly decreased the maximum bending moment (by ~50%) and lateral displacement, highlighting their critical role in optimizing performance. These findings directly inform the design of marine structures by optimizing embedment depth and load frequency to mitigate cyclic degradation, ensuring the long-term serviceability of FRP composite piles in corrosive, high-cycle marine environments.

To rapidly and precisely calculate the slender pile response and the soil resistance under lateral load in offshore wind power projects, the energy-based variational method was used to improve the calculation method of laterally loaded slender piles in layered elastic soil. Firstly, two cases were collected, the results were compared with that from the m-method, and numerical analysis or measured data were used to verify the accuracy of the improved method in this paper. Then, from the field test of a steel pipe pile in an offshore wind power project, the results from the improved method were compared with those from the numerical analysis and measured data, and the lateral soil resistance considering the layered shear effect and the distributed moment around the pile were discussed. The results show that the improved method in this paper can rapidly and precisely calculate the slender pile response under lateral load, and there is a 9~20% difference in the lateral soil resistance if the shear effect between each soil layer is considered. The ratio of the total distributed moment around the pile and the overturning moment at the pile head is less than 2%, and the resistance coefficient of m from this method provides the lower bound solution of the measured value.