Search Results (83)

High-viscosity stratified strata, characterized by complex geotechnical properties such as strong cohesion, low permeability, and pronounced layered structures, exhibit significant lateral friction resistance and high-end resistance during steel sheet pile installation. These factors substantially increase construction difficulty and may even cause structural damage. This study addresses two critical mechanical challenges during vibratory pile driving in Fujian Province’s hydraulic engineering project: prolonged high-frequency driving durations, and severe U-shaped steel sheet pile head damage in high-viscosity stratified soils. Employing the Coupled Eulerian–Lagrangian (CEL) numerical method, a systematic investigation was conducted into the penetration resistance, stress distribution, and damage patterns during vibratory pile driving under varying conditions of cohesive soil layer thickness, predrilled hole spacing, and aperture dimensions. The correlation between pile stress and penetration depth was established, with the influence mechanisms of key factors on driving-induced damage in high-viscosity stratified strata under multi-factor coupling effects elucidated. Finally, the feasibility of predrilling techniques for resistance reduction was explored. This study applies the damage prediction model based on the CEL method to U-shaped sheet piles in high-viscosity stratified formations, solving the problem of mesh distortion in traditional finite element methods. The findings provide scientific guidance for steel sheet pile construction in high-viscosity stratified formations, offering significant implications for enhancing construction efficiency, ensuring operational safety, and reducing costs in such challenging geological conditions. Full article

The implantable capsule grouting pile is a novel pile foundation technology in which a capsule is affixed to the side of the implanted pile to facilitate grouting and achieve extrusion-based reinforcement. This technique is designed to improve the bearing capacity of implanted piles in coastal areas with deep, soft soil. This study conducted model tests involving multiple grouting positions across different foundation types to refine the construction process and validate the enhancement of bearing capacity. Systematic measurements and quantitative analyses were performed to evaluate the earth pressure distribution around the pile, the resistance characteristics of the pile end, the evolution of side friction resistance, and the overall bearing performance. Special attention was given to variations in the lateral friction resistance adjustment coefficient under different working conditions. Furthermore, an actual case analysis was conducted based on typical soft soil geological conditions. The results indicated that the post-grouting process formed a dense soil ring through the expansion and extrusion of the capsule, resulting in increased soil strength around the pile due to increased lateral earth pressure. Compared to conventional piles, the grouted piles exhibited a synergistic improvement characterized by reduced pile end resistance, enhanced side friction resistance, and improved overall bearing capacity. The ultimate bearing capacity of model piles at different grouting depths across different foundation types increased by 6.8–22.3% compared with that of ordinary piles. In silty clay and clayey silt foundations, the adjustment coefficient η_s of lateral friction resistance of post-grouting piles ranged from 1.097 to 1.318 and increased with grouting depth. The findings contribute to the development of green pile foundation technology in coastal areas. Full article

This study investigates the response of laterally loaded pile foundations embedded in sloping beds under scour conditions, which is vital for the design and stability of coastal and offshore infrastructure like sea-crossing bridges, offshore wind turbines, and wharves. While previous studies have focused on scour-affected pile performance in horizontal beds, this research expands the scope by incorporating sloped beds and corresponding scour effect, which are common in coastal and offshore environments. A three-dimensional finite element model was established to evaluate the pile foundation’s lateral load-bearing capacity under different slope and scour conditions, according to preceding flume tests on the mechanism of local scour around a pile in sloping bed. The results indicate that the lateral response of the pile is significantly influenced by the seabed slope and scour depth. A negatively inclined seabed weakens the interaction between the pile and the surrounding sediment, thereby reducing the lateral bearing capacity and bending moment. As the scour depth increases, the support provided by the soil further weakens, intensifying the reduction in lateral resistance. This effect is particularly pronounced for steep negative slopes, where the combined impact of slope and scour has a more significant detrimental effect. Full article

The continued upscaling of offshore wind turbines (OWTs) necessitates the development of foundation systems capable of sustaining increased lateral loads. As monopiles remain the most widely used foundation type for OWTs, a detailed investigation into their lateral behavior and soil flow under operational loading is warranted. This study utilized a nonlinear three-dimensional finite element model (FEM) to assess the lateral performance of monopiles supporting a 5 MW turbine in clayey soils. The results revealed that the lateral capacity and deformation behavior are governed primarily by soil shear strength and the monopile’s length-to-diameter ratio (L/D). In softer soils, increasing the L/D ratio led to notable enhancements in lateral resistance, up to fivefold, as well as significant reductions in pile head displacement and rotation. In contrasts, monopiles in stiff clay exhibited distinct failure patterns and less sensitivity to L/D variations. Soil deformation patterns at the ultimate state varied depending on stiffness, indicating distinct failure mechanisms in soft and stiff clays. These findings highlight the importance of incorporating realistic soil behavior and geometric influences in monopile foundation design for large OWTs. Full article

In order to study the bearing characteristics of pile groups under the coupling of multiple caves, the influence of the interaction between the crossing cave, the underlying inclined cave, the pile-side cave, and the underlying cave on the ultimate bearing capacity, axial force, lateral friction, and load sharing ratio of the pile group was analyzed based on the model test. The research results show the following: (1) Due to the existence of the underlying cave, the Q-S curves of the pile groups are all steep drop types, and they show the characteristics of end-bearing piles. The influence of other caves is not obvious; the existence of beaded caves, lower crossing caves, underlying inclined caves, upper crossing caves, and pile-side caves will reduce the ultimate bearing capacity of the pile group. The reduction in the ultimate bearing capacity is 7.38%, 4.94% for the lower crossing cave, 2.59% for the underlying inclined cave, 2.27% for the upper crossing cave, and 0.74% for the pile-side cave. (2) When the pile body passes through the cave, the axial force changes slightly in the overburden layer, changes greatly in the limestone layer, and remains unchanged in the cave; under the same load level, the axial force of the pile close to the underlying inclined cave and the pile-side cave is smaller than that of the pile farther away. (3) Under the same load level, the lateral friction of the pile foundation shows a decreasing trend in the sand layer and limestone layer. The friction inside the sand layer is small. After entering the lime layer, the lateral friction increases sharply. The lateral friction is approximately 0 within the cave range. After passing through the cave, the lateral friction increases sharply. (4) The underlying inclined cave and the pile-side cave do not affect the position of the peak point of the pile foundation. The existence of the cave makes the pile foundation increase the peak point at the exit of the cave; under the same load level, the lateral friction of the pile close to the underlying inclined cave and the pile-side cave is larger than that of the pile farther away. (5) The existence of beaded caves, lower crossing caves, underlying inclined caves, upper crossing caves, and pile-side caves will increase the proportion of pile end resistance by 6.95%, 4.23%, 0.94%, 0.77%, and 0.62%, respectively. (6) This study systematically analyzed the differences in the degree of influence of different types of caves (including crossing caves, underlying inclined caves, and pile-side caves) on the bearing characteristics of pile foundations under the condition of the existence of underlying caves. It was found that beaded caves > lower crossing caves > underlying inclined caves > upper crossing caves > pile-side caves, which provides a priority decision-making basis for the optimal design of cave treatment schemes in engineering practice. Full article

This numerical study utilizes a validated Plaxis 3D model calibrated against full-scale field tests to investigate the lateral load-sharing mechanism of the pile cap in a 3 × 3 pile group under horizontal loading. Numerical simulations calibrated against full-scale field tests reveal that the pile cap significantly enhances the lateral bearing capacity while reducing horizontal displacement by an average of 59.5%. The load-sharing ratio of the pile cap decreases from 62% at low loads to 50% at higher loads, with a corresponding increase in pile contributions. The decomposition of the pile cap’s resistance identifies passive earth pressure (P_C-E) as the dominant component (72–80%), followed by base friction (P_C-B, 15–18%) and side friction (P_C-S, 5–12%). According to parametric analyses, increasing the embedment depth (H) from 0.5 m to 3.0 m elevates the pile cap’s load-sharing ratio by approximately 60%, while expanding the cap width (B) from 2.5 m to 3.5 m enhances lateral resistance by increasing the contact area. A power function relationship quantifies the load-sharing ratio (β) as a function of the product of H and B. These findings provide critical insights for optimizing pile cap geometry and improving the design of laterally loaded pile group foundations. Full article

The NT-CEP pile is an innovative type of pile that builds upon the conventional concrete straight-hole cast-in-place pile. It primarily consists of two components: the main pile and the bearing plate. The key factors influencing its load-bearing capacity include the pile diameter, the cantilever dimensions of the bearing plate, and the slope of the bearing plate’s foot, among others. The pile spacing significantly influences the bearing capacity of NT-CEP pile group foundations. The overall bearing capacity of an NT-CEP pile group foundation is not merely the sum of the ultimate bearing capacities of individual piles; rather, it results from the interactions among the pile bodies, the cap, and the foundation soil. Advancing the design theory of NT-CEP pile groups and enhancing their practical applications in engineering requires an in-depth investigation of how different pile spacings influence the load-bearing performance of pile group foundations. This objective can be achieved by exploring the soil damage mechanisms around side, corner, and central piles. This exploration helps in clarifying the influence of pile spacing on the load-bearing performance. Based on research findings regarding the bearing capacity of single and double pile foundations, this paper utilizes ANSYS finite element simulation analysis to model six-pile and nine-pile groups. Because these arrangements are universally adopted in engineering practice, they are capable of accounting for the pile group effect under various pile spacings and row configurations. The nine-pile group comprises corner piles, side piles, and a center pile, enabling a comprehensive analysis of stress variations among piles at different positions. As six-pile and nine-pile groups represent common pile configurations, studying these two types can provide valuable insights and direct references for optimizing pile foundation design. The study systematically investigates the influence of varying piles spacings on the bearing capacity of NT-CEP pile group foundations. It concludes that, as pile spacing decreases, The displacement of the top of this pile increases. thereby enhancing the group piles effects. Conversely, increasing the spacing between piles represents an effective strategy for elevating the compressive capacity of the NT-CEP pile-group foundation. Larger spacing also increases the vertical load-bearing capacity of the central piles, enhances the lateral friction resistance of corner piles, and heightens the load-sharing proportion between the bearing plate and the pile end. Furthermore, increasing pile spacing raises the ratio of load sharing by the foundation soil for both the CEP nine-pile foundation and the CEP six-pile foundation. The reliability of the simulation study has been verified by a visualization small scale model test of a half cut pile. Full article

The structural clay of the Zhanjiang Formation exhibits significant thixotropy, and there are considerable differences in the ultimate bearing capacity of pulled-out piles under different resting times. Using the structural clay from the Zhanjiang Formation as the foundation, direct shear tests on the soil surrounding nine groups of model single piles of different sizes were conducted at various resting times, along with static pullout tests on the pile foundations. The results indicate that the cohesion and internal friction angle of the surrounding soil increase following a logarithmic function with increasing resting time; specifically, the growth rate is rapid in the early resting period and gradually slows down in the later period. A quantitative relationship describing the variation of cohesion and internal friction angle over time was established. The load–displacement curves for single piles at different resting times exhibit a distinct steep drop. The uplift single pile exhibits significant time-dependency, with the ultimate uplift bearing capacity increasing more rapidly in the early stages and gradually stabilizing in the later stages. Under different resting times, for each load level, the maximum side friction resistance of the pile gradually shifts to the middle and lower parts of the pile body, while the ultimate side friction resistance is evenly distributed along the lower part of the pile body, with the side friction resistance of the pile bearing the uplift load. Based on the quantitative relationship of the cohesion and internal friction angle of the surrounding soil around the pile varying with time, a predictive formula for the axial pullout ultimate bearing capacity of a single pile in the Zhanjiang Group structured clay foundation has been established. Using existing pile foundation projects, model experiments were designed to verify the validity of the formula; however, there is a lack of field-scale validation. The research findings can provide a reference for predicting the axial pullout ultimate bearing capacity of single piles in practical engineering applications. Full article

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. Full article

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. Full article

The population surge has led to a corresponding increase in the demand for high-rise buildings, bridges, and other heavy structures. In addition to gravity loads, these structures must withstand lateral loads from earthquakes, wind, ships, vehicles, etc. A piled raft foundation (PRF) has emerged as the most favored system for high-rise buildings due to its ability to resist lateral loads. An experimental study was conducted on three different piled raft model configurations with three different relative densities (D_r) to determine the effect of D_r on the lateral response of a PRF. A model raft was constructed using a 25 mm thick aluminum plate with dimensions of 304.8 mm × 304.8 mm, and galvanized iron (GI) pipes, each 457.2 mm in length, were used to represent the piles. The lateral and vertical load cells were connected to measure the applied loads. It was found that an increase in D_r increased the soil stiffness and led to a decrease in the lateral displacement for all three PRF models. Additionally, the contribution of the piles in resisting the lateral load decreased, whereas the contribution of the raft portion in resisting the lateral load increased. With an increase in D_r from 30% to 90%, the percentage contribution of the raft increased from 42% to 66% for 2PRF, 38% to 61% for 4PRF, and 46% to 70% for 6PRF. Full article

This study presents three-dimensional finite element analyses of two marine structures subjected to lateral loading to approximate environmental forces (e.g., wind, waves, currents, earthquakes). The first structure is a marine jetty supported by twenty-four piles, representative of an existing structure in Cyprus, while the second is a simplified four-pile marine structure. Soil–pile interaction is modelled using nonlinear p-y, τ-z, and q-z springs that are distributed along the piles, while steel plasticity is also considered. This study examines the relationship between failure modes, deformation modes, and plastic hinge locations with soil behaviour and soil reaction forces. It also aims at investigating the behaviour of the above structures in lateral loading and quantifying the consequences of unrealistic assumptions such as soil and steel linearity or tension-resistant q-z springs. The results indicate that such assumptions can lead to the wrong prediction of failure modes, plastic hinges, and critical elements while emphasising the crucial role of soil nonlinearity and axial pile–soil behaviour on the structural response. It is demonstrated that the dominant nonlinear sources relevant to this study, whether soil nonlinearity, plastic hinge formation, or a combination of the two, are primarily influenced by the axial capacity of soil–pile foundation systems, particularly their tensile component. Full article

The investigation of new composite materials possessing low weight but not at the expense of their mechanical performance is of great interest in terms of reducing energy consumption in many industrial applications. This study is focused on the nanomechanical characterization of high-density polyethylene (HDPE)-based composite specimens modified with equal loadings of graphene nanoplatelets (GNPs) and/or multiwall carbon nanotubes (MWCNTs). Quasi-static nanoindentation analysis revealed the impact of the carbon nanofillers on the receiving of nanocomposites with higher nanohardness and reduced modulus of elasticity, reaching values of 0.146 GPa and 3.57 GPa, respectively. The role of the indentation size effect in elastic polymer matrix was assessed by applying three distinct peak forces. Nanoscratch experiments depicted the tribological behavior of the composite samples and inferred the influence of the carbon nanofillers on the values of the coefficient of friction (COF). It seems that the incorporation of 4 wt% GNPs in the polymer structure improves the scratch resistance of the material, resulting in a higher value of the exerted lateral force and therefore leading to the detection of a higher coefficient of friction at scratch of 0.401. A considerable pile-up response of the scratched polymer specimens was observed by means of in-situ SPM imaging of the tested surface sample area. The sway of the carbon nanoparticles on the composite pile-up behavior and the effect of the pile-up on the measured friction coefficients have been explored. Full article

Horizontal resistance can be significantly different for gravelly soil slope sites with different gradients. The impact of slope gradient on the horizontal resistance of soil based on a three-dimensional physical simulation test has been investigated, and the displacement of the pile top and soil pressure for four piles under various gradients (slope gradient 0–45°) was analyzed. The research reveals that ① The soil resistance exhibits a linear increase stage, non-linear steep increase stage, and gradually stabilizing stage with the increase in load. ② The ultimate soil resistance is significantly affected by depth and displacement, and hyperbolic variation characteristics related to the displacement stage. It has a slope weakening effect, and the steeper the slope gradient, the lower the ultimate soil resistance of the pile sides, which effect is negligible when the depth exceeds 0.6–0.7 times that of the pile buried depth. ③ Based on the characteristics of horizontal ultimate resistance-displacement-depth variation in soil, a gradient factor, which is only related to the slope gradient, was used to describe the impact of gradient on the soil resistance modulus (k_ini) and ultimate resistance (p_u). k_ini is reduced close to the ground surface and gradually increases with depth until it becomes equal to the value of level ground. The ratio between p_u in slope ground and level ground was determined for slope angles. The above horizontal resistance parameters were expressed as a function based on the test data to calculate the lateral ultimate bearing capacity of gravelly soil considering the slope gradient factor. The research results developed the theory of foundation design for building structures, promoting the reliability evaluation of pile soil systems towards a more scientific and rigorous direction. 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