In this study, the effect of near-field and far-field ground motions on the seismic response of the soil pile system is investigated. The forward directivity effect, which includes a large velocity pulse at the beginning of the velocity time history of the ground motion is the most damaging phenomenon observed in near-field ground motions. To investigate the effect of near-field and far-field ground motions on the seismic response of a soil-pile system, a three-dimensional model consisting of the two-layer soil, liquefiable sand layer over dense sand, and the pile is utilized. Modeling is conducted in FLAC 3D software. The P2P Sand constitutive model is selected for sandy soil. Three fault-normal near-field and three far-field ground motion records were applied to the model. The numerical results show that near field velocity pulses have a considerable effect on the system behavior and sudden huge displacement demands were observed. Also, during the near-field ground motions, the exceeded pore water pressure coefficient (Ru) increases so that liquefaction occurs in the upper loose sand layer. Due to the pulse-like ground motions, a pulse-like relative displacement is created in response to the pile. Meanwhile the relative displacement response of the pile is entirely different due to the energy distribution during the far-field ground motions.

Soft soil subgrades often present significant geotechnical challenges under cyclic loading conditions associated with major infrastructure developments. Moreover, there has been a growing interest in employing various recycled tire derivatives in civil engineering projects in recent years. To address these challenges sustainably, this study investigates the performance of granular piles incorporating recycled tire chips as a partial replacement for conventional aggregates. The objective is to evaluate the cyclic behavior of these tire chip-aggregate mixtures and determining the optimum mix for enhancing soft soil performance. A series of laboratory-scale, stress-controlled cyclic loading tests were conducted on granular piles encased with combi-grid under end-bearing conditions. The granular piles were constructed using five volumetric proportions of (tire chips: aggregates) (%) of 0:100, 25:75, 50:50, 75:25, and 100:0. The tests were performed with a cyclic loading amplitude (qcy) of 85 kPa and a frequency (fcy) of 1 Hz. Key performance indicators such as normalized cyclic induced settlement (Sc/Dp), normalized excess pore water pressure in soil bed (Pexc/Su), and pile-soil stress distribution in terms of stress concentration ratio (n) were analyzed to assess the effectiveness of the different mixtures. Results indicate that the ordinary granular pile (OGP) with (25 % tire chips + 75 % aggregates) offers an optimal balance between performance and sustainability. This mixture reduced cyclic-induced settlement by 86.7 % compared to the OGP with (0 % TC + 100 % AG), with only marginal losses in performance (12.3 % increase in settlement and 2.8 % reduction in stress transfer efficiency). Additionally, the use of combi-grid encasement significantly improved the overall performance of all granular pile configurations, enhancing stress concentration and reducing both settlement and excess pore water pressure. These findings demonstrate the viability of using recycled tire chips as a sustainable alternative in granular piles, offering both environmental and engineering benefits for soft soil improvement under cyclic loading.

Post-grouting pile technology has gained extensive application in collapsible loess regions through the injection of slurry to compress and consolidate the soil at the pile base, thereby forming an enlarged base that enhances the foundation's bearing capacity and reduces settlement. Despite the prevalent unsaturated state of loess in most scenarios, the conventional design methodologies for piles in collapsible loess predominantly rely on saturated soil mechanics principles. The infiltration of water can significantly deteriorate the mechanical properties of loess due to the reduction in matric suction and the occurrence of collapsible deformation, leading to a substantial degradation in the bearing behavior of piles. To explore the variations in load transfer mechanisms of post-grouting piles in collapsible loess under conditions of intense precipitation, a comprehensive large-scale model test was conducted. The findings revealed that the post-grouting technique effectively mitigates the adverse effects of negative pile shaft friction in saturated zones on the pile's bearing behavior. Furthermore, the failure criteria for piles may shift from the shear failure of the base soil to excessive pile settlement. By incorporating principles of unsaturated soil mechanics, modified load transfer curves were developed to describe the mobilization of both pile shaft friction and base resistance. These curves facilitate the extension of the traditional load transfer method to post-grouting piles in collapsible soils under extreme weather conditions. The proposed revised load transfer method is characterized by its simplicity, requiring only a few soil indices and mechanical properties, making it highly applicable in engineering practice.

The cyclic behavior of clay significantly influences the dynamic response of offshore wind turbines (OWTs). This study presents a practical bounding surface model capable of describing both cyclic shakedown and cyclic degradation. The model is characterized by a simple theoretical framework and a limited number of parameters, and it has been numerically implemented in ABAQUS through a user-defined material (UMAT) subroutine. The yield surface remains fixed at the origin with isotropic hardening, while a movable projection center is introduced to capture cyclic hysteresis behavior. Cumulative plastic deviatoric strain is integrated into the plastic modulus to represent cyclic accumulation. Validation against undrained cyclic tests on three types of clay demonstrates its capability in reproducing stress-strain hysteresis, cyclic shakedown, and cyclic degradation. Additionally, its effectiveness in solving finite element boundary value problems is verified through centrifuge tests on large-diameter monopiles. Furthermore, the model is adopted to analyze the dynamic response of monopile OWTs under seismic loading. The results indicate that, compared to cyclic shakedown, cyclic degradation leads to a progressive reduction in soil stiffness, which diminishes acceleration amplification, increases settlement accumulation, and results in higher residual excess pore pressure with greater fluctuation. Despite its advantages, this model requires a priori specification of the sign of the plastic modulus parameter cd to capture either cyclic degradation or shakedown behavior. Furthermore, under undrained conditions, the model leads pstabilization of the effective stress path, which subsequently results in underestimation of the excess pore pressure.

Pile foundations are frequently used in the construction of bridges, offshore platforms, and offshore wind turbines, which are often subjected to complex lateral cyclic loading from wind, wave, or current. These lateral loads usually come from different directions or constantly change their direction, which is ignored by most existing calculation models. A two-dimensional p -y model is proposed in this study for the lateral response of the pile subjected to multi-directional cyclic loading in sand. Without introducing additional parameters, the p -y response in two dimensions is coupled by developing the model within the framework of the bounding surface p -y model. Combined with the collapse and recompression model, the effect of sand collapse around the pile during cyclic loading is considered to approach reality. The pile lateral displacement and soil resistance are obtained in incremental form using the finite difference method in the two-dimensional case. By comparing with the model test results, it is demonstrated that the proposed model is able to reasonably predict the lateral cyclic response of the pile as well as the effects of multi-directional cyclic loading. The distribution and variation characteristics of the soil resistance are further discussed by analyzing the results calculated by the proposed model.

Open-ended pipe piles (OEPPs) are widely used in offshore foundations, yet accurately predicting their driving responses remains challenging due to soil plug complexities. Existing pile driving analysis models inadequately characterize the effects of soil plug, potentially leading to driving problems such as hammer refusal, pile running, and structural damage. This paper proposes an effective soil plug (ESP) model for OEPP driving analysis. The ESP model considers the effective range of soil plug, which exerts internal resistance that increases exponentially with depth while the beyond of effective range contributes only mass inertia. It also accounts for the relative slippage at the pile-soil plug interface. A differential iterative method is developed to solve the ESP model. Subsequently, investigations including the model validation and parameter analysis are conducted. Model validations against existing models and field measurements confirms the reliability of the ESP model. Parameters sensitivity analysis reveals the importance of soil plug length and distribution type of internal resistance on the pile dynamic responses. In addition, if soil plug slippage occurs, the displacement peak of soil plug increases with depth rather than one-dimensional wave attenuation. Furthermore, contrary to previous assumptions of continuous slippage, the soil plug experiences a discontinuous jump-sliding mode under long-duration impact loading. These findings provide theoretical basis for OEPP driving simulation and interpretations of high-strain dynamic test.

A series of large-scale shaking table tests were conducted to investigate the dynamic response and damage characteristics of the variable- single pile foundation in liquefiable soil-rock interaction strata under seismic loading. The test results show that the seismic responses of the excess pore pressure ratio under seismic excitations are divided into four stages, among which the difference in the sustained liquefaction stage is the most significant. Pile acceleration amplification is governed by dual coupling effects of soil-pile interaction and structural stiffness. The pile body bending moment distribution features dual-peak characteristics, the largest peak arises at the soil layers interface, while the other peak occurs at the variable-section. Increased seismic excitation accelerates the liquefaction of the saturated sand layer, yet simultaneously slows down the dissipation of the excess pore pressure. As the seismic excitation increases, the acceleration response and displacement response of the pile top are most significant, though maximum bending moment positions remain stable. The stress overrun damage occurs gradually in the variable- zone under strong earthquakes. Based on the analysis results and the Fourier spectrum modal characteristics of the pile top, the damage mechanism of the pile body is revealed and verified. This study will provide an essential reference for further understanding the seismic response and damage of the variable- single pile foundation in liquefiable soil-rock interaction strata.

The incorporation of PCMs in energy piles holds significant potential for revolutionising thermal management in construction, making them a crucial component in the development of next-generation systems. The existing literature on PCM-integrated energy piles largely consists of isolated case studies and experimental investigations, often focusing on specific aspects without providing a comprehensive synthesis to guide future research or practical applications. To date, no review has been conducted to consolidate and evaluate the existing knowledge on PCMs in energy piles, making this review the first of its kind in this field. Up until now, this gap in research has limited our understanding of how PCM configurations, thermal properties, and integration methods impact the thermal and mechanical performance of these systems. Through thoroughly analysing the current research landscape, this review discovers key trends, methodologies, and insights. The methodology used here involved a systematic search of the existing SCI/SCIE-indexed literature to ensure a structured review. Based on the SLR findings, it is evident that current research on PCMs in energy piles is focused on improving thermal efficiency, heat transfer, and compressive strength. Furthermore, precise adjustments in melting temperature significantly impact efficiency, with PCM integration boosting thermal energy extraction by up to 70 % in some cases, such as heating cycles, and saving up to 30 % in operational costs. PCMs also reduce soil temperature fluctuations, improving structural integrity through minimising axial load forces. However, challenges remain, including reduced mechanical strength due to voids and weak bonding, high costs, and complexities such as micro-encapsulation. We acknowledge that there are gaps in addressing certain key factors, including thermal diffusivity; volume change during phase transitions; thermal response time; compatibility with construction materials; interaction with soil, creep, and fatigue; material compatibility and durability; and the long-term energy savings associated with PCM-GEP systems.

Pile penetration in soft ground involves complex mechanisms, including significant alterations in the soil state surrounding the pile, which influence the pile negative skin friction (NSF) over time. However, the pile penetration process is often excluded from finite element analysis. This paper investigates the impact of pile penetration on the generation of NSF and dragload. A stable node-based smoothed particle finite element method (SNS-PFEM) framework is introduced for two-dimensional axisymmetric conditions and coupled consolidation, incorporating the ANICREEP model of soft soil with a modified cutting-plane algorithm. A field case study with penetration process is simulated to verify the numerical model's performance, followed by a parametric analysis on the effect of penetration rate on NSF during consolidation. Results indicate that without the pile penetration process in NSF analysis can result in an unsafely low estimation of NSF and dragload magnitudes. The penetration rate affects dragload only at the initial consolidation stage. As consolidation progresses, dragload converges to nearly the same magnitude across different rates. Additionally, current design methods inadequately predict the beta value (where beta is an empirical factor correlating vertical effective stress of soil with the pile skin friction) and its time dependency, for which a new empirical formula for the time-dependent beta value is proposed and successfully applied to other field cases.

Energy piles, which serve the dual functions of load-bearing and geothermal energy exchange, are often modeled with surrounding soil assumed to be either fully saturated or completely dry in existing design and computational methods. These simplifications neglect soil saturation variability, leading to reduced predictive accuracy of the thermomechanical response of energy piles. This study proposes a novel theoretical framework for predicting the thermo-hydro-mechanical (THM) behavior of energy piles in partially saturated soils. The framework incorporates the effects of temperature and hydraulic conditions on the mechanical properties of partially saturated soils and pile-soil interface. A modified cyclic generalized nonlinear softening model and a cyclic hyperbolic model were developed to describe the interface shear stress-displacement relationship at the pile shaft and base, respectively. Governing equations for the load-settlement behavior of energy piles in partially saturated soils were derived using the load transfer method (LTM) and solved numerically using the matrix displacement method. The proposed approach was validated against experimental data from both field and centrifuge tests, demonstrating strong predictive performance. Specifically, the average relative error (ARE) was less than 15% for saturated soils and below 23% for unsaturated soils when evaporation effects were considered. Finally, parametric analyses were conducted to assess the effects of flow rate, groundwater table position, and softening parameters on the THM behavior of energy piles. This framework can offer a valuable tool for predicting THM behavior of energy piles in partially saturated soils, supporting their broader application as a sustainable foundation solution in geotechnical engineering.