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Previous earthquake events indicate that pile foundations in liquefiable soils are vulnerable to damage due to the coupling of inertial and kinematic effects. Inclined piles are widely applied in structures located in liquefiable soils, but few investigations of the coupling of the superstructure–pile inertial and soil–pile kinematic effects have been conducted. To address this gap, this study adopted a three-dimensional (3D) numerical model to investigate the coupling of inertial and kinematic effects in pile foundations with different inclination angles. The pile head bending moment was employed to represent the pile response, while the soil surface displacement and structure acceleration were utilized to quantify the kinematic and inertial effects. The role of the inclination angle on the interactions between inertial and kinematic effects is herein considered for pile groups. In particular, the inertial effect significantly influences the behavior of pile groups with larger inclination angles, whereas the kinematic effect predominates the pile head moment in vertical pile groups. In this paper, the influence of the pile inclination angle, superstructure configuration, and earthquake intensity on the interactions was investigated. The principal findings revealed that the kinematic effect dominates in the vertical pile group irrespective of the properties of the superstructure, while the inertial effect plays a significant role in the response of the inclined pile groups, especially for superstructures with considerable heights. Practical Applications: Inclined piles are vulnerable to damage due to the interaction of inertial and kinematic effects during earthquakes. This study conducted a series of three-dimensional (3D) finite-element simulations to investigate the interaction of inertial and kinematic effects in pile foundations with different inclination angles. The influence of pile inclination angle, superstructure height, and earthquake characteristics was investigated. In current practices, various codes and pseudostatic methods have been adopted to sum a percentage of the inertia-induced bending moment and another percentage of the kinematic-induced bending moment. This study indicates that under certain conditions, the simple summing of the bending moment induced by the inertial and kinematic effects could be inaccurate. The present study identified several factors that influence the interaction of inertial and kinematic effects on piles with different inclination angles. The inclined piles in liquefied soil, especially for supporting tall and heavy superstructure, attention should be given to the influence of inertial effect on the pile head bending moment. [ABSTRACT FROM AUTHOR]

A comprehensive experimental program was performed in order to understand the mechanical behavior of model piles associated with water infiltration in collapsible loess. Real-time measurements were recorded for pile head settlement, pile shaft friction, and pile base resistance, as well as for the soil behavior, including soil settlement, volumetric water content, and soil suction. The experimental results suggest that both the pile head settlement and pile base resistance increased with water infiltration. The linear pile axial force distribution gradually changed to a "D" shape, with the maximum pile axial force occurring in the middle instead of the end stage of water infiltration. Such behavior can be attributed to a reduction in the contribution of soil suction, degradation of the pile–soil interface shear strength, and settlement of the collapsible soil. In addition, a softening model was proposed by modifying the traditional shear displacement method for interpretation of the mechanical behavior of piles in collapsible loess. There was good agreement between our experimental results and those from the literature and the results predicted using the proposed model, suggesting that the model can be used as a tool in the rational design of pile foundations in collapsible soils. [ABSTRACT FROM AUTHOR]

Piled embankments are becoming widely used to cope with engineering problems (e.g., excessive settlements, bearing failure) caused by soft soil subgrade to maintain the safety and stability of the constructed facilities. This study focused on an international motor-racing circuit currently under construction, where the underlying soft soil substratum characterized by a high void ratio and compressibility may largely influence the long-term performance of the project. Pretensioned high-strength concrete (PHC) pile-supported embankment is designed to improve this project, and its effectiveness remains to be studied. In addition, this study specifically focused on negative skin friction (NSF) and neutral plane (NP) position development, which significantly influence the bearing capacity of the pile foundation and have not been fully understood. As such, two large-scale field tests were performed on the PHC pile-supported embankments to monitor the settlement of piles and the surrounding soils. According to the monitored layered settlements, the NP development with time was quantitatively analyzed, and NP gradually moved up toward the pile top during soil consolidation. Comparison between the measurements of two test sites with and without geogrid reinforcement indicated that geogrids could not only alleviate total and differential settlements of the foundation but also contribute to the shallower final NP position. A numerical model, whose effectiveness was validated by comparing with the field measurements, was established to predict the complete variation of NP positions and explore the effects of various influencing factors through a parametric study. This study enhances the comprehension of NSF and NP development in pile foundations and provides valuable guidance for this motor-racing circuit and other related projects in the future. [ABSTRACT FROM AUTHOR]

At present, the reliability analysis and design method of vertically loaded piles embedded in spatially variable soils is difficult to be applied in practical engineering due to the huge computation effort required. To improve computational efficiency, this paper proposes a new method called the FORM–KL–LTM, which integrates the advantages of the first-order reliability method (FORM), the Karhunen–Loève (KL) expansion method, and the load transfer method (LTM). The main framework of the FORM–KL–LTM is the FORM, which is used to perform reliability analysis for the pile. The KL expansion method is adopted to carry out random discretization to generate the discrete soil parameters required by each iterative computation of the reliability index using the FORM, and the LTM is employed to evaluate the nonlinear load–settlement behavior of the pile head and to compute the values of limit state functions required by the FORM. The proposed method is computationally efficient because the number of random variables is controlled by the limit number of KL expansion terms. Based on the FORM–KL–LTM, a reliability sensitivity analysis method is proposed, which can compute the sensitivity index for measuring the relative sensitivity of the reliability index with respect to soil properties. Furthermore, a procedure for the reliability-based design (RBD) of piles embedded in spatially variable soils is established for the design of pile geometry, and a design ratio is defined to select the controlling limit state in the RBD of pile for both the ultimate limit state and the serviceable limit state. The procedure, accuracy, and efficiency of the proposed methods are demonstrated by providing an example of the reliability analysis and design of a vertically load pile in spatially variable soils. The spatial variability of soil has been recognized as an important source of uncertainty of the bearing performance of the pile, and therefore, it should be considered in the reliability analysis and design of a pile foundation. However, the methods used in the current literature, such as the discretization of a random field, the calculation of load–displacement curves, and the reliability analysis of a pile foundation, require a huge computation effort. Low computational efficiency is highly disadvantageous to designers, which makes the reliability analysis and design method by considering a soil's spatial variability difficult to be widely applied to practical engineering. Therefore, this study proposes a new method called the FORM–KL–LTM to perform the reliability analysis and design of vertically loaded piles in spatially variable soils. This method greatly reduces the number of random variables and simulations of the performance function, thus improving the computational efficiency. Based on the FORM–KL–LTM, a reliability sensitivity analysis method is proposed to carry out a sensitivity analysis of soil parameters on the reliability of a pile foundation. Moreover, this paper defines the design ratios for discussing which limit state mainly controls the failure state of the pile foundation under different soil properties and pile geometry. [ABSTRACT FROM AUTHOR]

Existing projects indicate that a large number of pile boreholes formed via cement fly ash gravel (CFG) pile construction in soft soil could produce a borehole group effect in the absence of timely backfilling. The borehole group effect could cause ground settlement and threaten the safety of adjacent buildings, tunnels, and pipelines. However, the mechanism of the borehole group effect, causing serious deformation in surrounding soil, has seldom been studied, and there exists no simple simulation method to predict the borehole group effect. In this study, a case involving CFG pile boreholes in a soft soil area causing a significant settlement of surrounding buildings was introduced. Based on this case, a centrifuge test was designed to simulate the influence of a single borehole and multiple boreholes on the surrounding soft soil. The mechanism of the borehole group effect was investigated via centrifuge tests and the finite-element method. In the case of a single borehole, a horizontal circumferential stress arch and vertical stress transfer arch were formed in the soil, which effectively limited the shrinking deformation of the borehole wall. In the case of a large number of boreholes with a small spacing, the horizontal and vertical stress arches around the boreholes affected and weakened each other. As a result, the shrinking deformation of the borehole group was greater than that of the single borehole. In other words, the borehole group effect was found to cause serious deformation in the surrounding soil. To overcome the difficulty in the simulation of a large number of pile boreholes in engineering, the borehole-type conversion and multihole merging method was proposed. The simulation results indicated that the simplified method was reasonable. [ABSTRACT FROM AUTHOR]

Due to the large demand to produce clean and renewable energy, offshore wind farms are extensively being used to help with economic development. Offshore Wind Turbine (OWT) structures are usually supported by various types of foundations and its selection depends on several factors such as water depth, economic costs, construction methodologies, seabed bathymetry, soil characteristics, and load characteristics. The present State-of-the-Art review focuses on OWT-monopile foundation systems embedded in multi-layered soil strata subjected to aerodynamic and hydrodynamic loading conditions. The purpose of this study is to carry out a comprehensive review on the performance of OWT-monopile foundation structures to support the design and drafting choices and thereby provide an understanding to reduce the costs. Two specific subject areas are addressed in this paper: (1) Factors affecting the performance of OWT-Monopile Foundation Systems; and (2) Experimental modeling and numerical analyses of OWT-Monopile Foundation Systems. The immediate challenge to the design of OWTs is to analyze the dynamic response of the foundation structure when exposed to both aerodynamic and hydrodynamic loads acting simultaneously. The limitations of the existing guidelines point to the need for improved design methods to obtain an economical design of OWT-monopile foundations. The use of Finite Element (FE) models is effective in studying the functioning of OWT-monopile structures. The present study suggests the development of further numerical models and modifications to the existing ones to properly assess soil-monopile interactions. This study also suggests further investigations on the design and analysis of OWT-monopile foundations considering the effect of (i) aerodynamic and hydrodynamic loading conditions with soil-monopile interactions, and (ii) multi-layered seabed characteristics. [ABSTRACT FROM AUTHOR]

Time-dependent settlements of piled raft foundations embedded in consolidating clays were studied using three-dimensional (3D) finite-element analysis and critical state-based soil constitutive modified Cam-Clay (MCC) model. In this study, different small to large rectangular rafts connected to circular bored cast-in-situ piles resting on four different types of clays and with varying overconsolidation ratios (OCRs) (1, 2, and 5) for each clay under a single drainage condition were analyzed. The influence of various piled raft parameters (pile length, pile spacing, pile diameter, raft thickness) and soil parameters (Poisson's ratio of soil, soil critical state parameters, stress history of soil or OCR) on immediate and consolidation settlements of piled rafts were investigated. The detailed parametric study shows that critical state parameters and soil elastic properties have important roles in piled raft immediate and consolidation settlements. However, the pattern of parametric influence on immediate settlement and consolidation settlement is different. To capture the total settlement at the end of primary consolidation, a simple and quick calculation method for estimating the average soil subgrade modulus below the piled raft in consolidating clays is proposed through regression analysis and defining a combined influence parameter based on soil parameters, area ratio, and normalized loading. The results of the proposed method were compared with five case studies of piled raft foundations in various normally or overconsolidated clays showing satisfactory matches. It is believed that the proposed method will be very useful for design practitioners to get a quick estimate for the overall settlement of piled raft at the initial design stage. [ABSTRACT FROM AUTHOR]

Issue 1 The authors employed three-dimensional (3D) finite-element software Plaxis 3D ([1]) to model a ring foundation in a cohesive soil, where a quarter of the problem domain (i.e., a 90° sector of the domain) was discretized. The authors employed the commercial finite-element software, namely, Plaxis 3D, to determine the ultimate bearing capacity of ring foundations in cohesive soils. In particular, for both cases of rough and smooth foundations, Eq. (10) of the original paper cannot make a realistic prediction in terms of the change of undrained bearing capacity when the I k i value varies from 1 to 10. Rather, Eq. (10) of the original paper generates almost constant undrained bearing capacity with all I k i values for each interface condition (i.e., rough I q SB ult sb i 363 kPa and smooth case I q SB ult sb i 93 kPa). [Extracted from the article]

This paper proposes an efficient hybrid approach for analysis of the responses of piled-raft foundations subjected to coupled loads (combination of vertical loads, horizontal loads, and moments) in layered soils. The proposed method comprehensively accounts for pile-pile, pile-soil surface, soil surface-pile, and soil surface-soil surface interactions. Moreover, to capture the influence of embedment and active/passive effects of piles, a modified Vesic's subgrade modulus for embedded piles and passive piles was adopted. To avoid a large number of time-consuming integration processes, the shear displacement method and elastic foundation beam method were employed to calculate the vertical and horizontal responses of a single pile, respectively, and the results were then extended for the pile group. The results calculated with the proposed method for piled-raft foundations in layered soils were found to have good agreement with those obtained from the more rigorous finite-element methods (FEMs) and elastic theory method in layered soils. It was found that the proposed procedure can accurately predict the responses of piled-raft foundations under complex loads in layered soils. [ABSTRACT FROM AUTHOR]

Geosynthetics such as geogrids or geotextiles are often used for the reinforcement of weak soils. Much research has been performed to investigate the bearing capacity of reinforced shallow foundations using the limit equilibrium method with Mohr-Coulomb failure criterion. In this paper, the loading behavior of reinforced strip footings was studied numerically using a commercial finite difference program with a double-yield soil model. First, the load-settlement curve of an unreinforced strip footing was simulated using both Mohr-Coulomb failure criterion and the double-yield model. The simulated bearing capacities were then compared with Terzaghi's solution. The effects of various parameters, such as burial depth and length of the reinforcement, as well as arrangement of two reinforcement layers, were also studied. Results of this study indicate that the loading behavior of strip footings simulated with the double-yield model is more realistic, and the optimum burial depth and length of reinforcement obtained from this study also agree with values reported by previous investigators. [ABSTRACT FROM AUTHOR]