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The numerical simulation of boundary value problems involving a high number of pile-type structures, such as pile foundation systems of high-rise buildings, represents a standard task in computational geotechnics. Due to their ability to simplify the underlying pile modeling process and decrease the simulation runtime embedded beam formulations (EBFs) have attracted widespread interest from the geotechnical community. State-of-the art EBFs are typically equipped with nonlinear interface constitutive models to capture the soil–structure interaction behavior with reasonable accuracy. However, reliable information concerning the calibration of related parameters is limited, which decreases the confidence in the results obtained with EBFs. The present work addresses this research aspect for the first time, along with a theoretical discussion of inherent simplifications in the numerical description of the soil–structure contact associated with EBFs. The significance of selecting adequate embedded interface constitutive model parameters to ensure EBF predictions with high credibility is demonstrated by means of parametric studies. This has motivated the development of an automatic calibration software, leveraged by particle swarm optimization, that provides guidance in selecting suitable values. The effectiveness of the calibration software is confirmed by back-calculation of different pile problems with default and calibrated parameter sets. Likewise, the results provide insight into crucial factors driving the calibration framework, with a view to increasing its potential for take-up in engineering practice. Potential lines of research in the context of the automatic calibration software are explored throughout this work and may serve as valuable reference in future research. Practical Applications: The design of geotechnical problems involving a high number of pile-type structures, such as pile foundation systems of high-rise buildings or wind turbines, is routinely assisted by finite-element analyses. The computational expense of these simulations is significantly influenced by the pile modeling technique. Due to their exceptional ability to simplify the underlying modeling process and reduce the runtime to an acceptable limit, embedded beam formulations have therefore attracted widespread interest for geotechnical design tasks. As with all soil–structure interaction problems, it is essential in embedded beam formulations to accurately describe the interface behavior between the soil and the structure. This work presents the first attempt to highlight the relevance of this concern and visually describes relevant limitations resulting from an inadequate selection of interface constitutive model parameters. This observation has motivated the development of an automatic calibration software to increase the confidence in the parameter selection. The high potential of this software to increase the credibility of numerical predictions obtained with embedded beam formulations is demonstrated based on pile problems with different soil stratification layers, pile geometries, and pile arrangements. In all cases considered, the results confirm that the numerical fidelity could be significantly increased by employing calibrated parameter sets. [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]

A database was compiled to establish the site-specific measured load–displacement responses of piles from different sites across the globe, which contains 188 curves from 12 sites. A curve-fitting technique was applied to each measured curve by using a two-parametric power law regression modeling. For an entire construction site, the scatter in the load–displacement behavior of multiple curves was incorporated in the uncertainty of the regression pairs. Consequently, environmental contours for regression pairs were developed by using the Nataf transformation or a normal copula. Such a contour was generated to quantify the uncertainty in the regression pairs in which the target reliability index of piles is specified, as demonstrated in various cases with two, three, and four variables. Most importantly, the environmental contour bounded by the serviceability limit state of piles at each site was presented and the reliability index was solved through an evolution of the environmental contours. The computed reliability index of the bearing resistance for piles was compared with the values yielded by the geometric reliability analysis and the first-order reliability method (FORM). Since the reliability index was solved in the original physical variable space, it made the reliability theory easy to understand. Such a site-specific reliability assessment of piles could be helpful for a practical project to implement quality control during the construction of pile foundations. [ABSTRACT FROM AUTHOR]

With the advantages of saving underground space, small construction impact, and saving cost, the double-O-tube (DOT) shield tunneling construction technology has been used many times in the tunnel construction of particular areas with dense buildings. This paper describes a device developed for modeling DOT shield tunneling based on transparent soil technology and investigating the displacement response of pile and soil during the construction process of a DOT shield tunnel adjacent to an existing pile, which is considered in the uniform convergence mode (UCM) of soil loss. Meanwhile, the displacement response of pile and soil in the nonuniform convergence mode (NCM) was analyzed contrastively using the discrete-element method (DEM). The results showed that the displacements of soils around the pile are limited and the shapes of the soil settlement curves above the DOT shield tunnel change approximatively from "V" to "W" with the depth of the soil layer increasing. When the buried depth of the pile was 1.0D, the settlements of the pile and soils were obviously affected by the convergence mode. The maximum surface settlements were 1.52, 1.34, and 1.21 times larger under NCM than those under UCM, while the maximum horizontal displacements of the vertical soil layer beside the pile were 1.92, 1.83, and 1.80 times larger under NCM than those under UCM, respectively, corresponding to H/D = 1.0, 1.5, and 2.0. With the buried depth of the DOT tunnel increasing, the deflection and settlement increased first and then decreased. When H/D = 2.0, the excavation of the DOT tunnel could barely cause pile deflection under NCM. [ABSTRACT FROM AUTHOR]

In nature, soil layers possess large variability during their geological process. This variability may also lead to differences in the location and thickness of nonliquefiable and liquefiable soil layers. In practice, the impact of liquefaction on the pile can be ignored at depths greater than 20 m due to high confining stress levels and a lack of liquefaction triggering data. On the other hand, this approach may underestimate design loads in many cases, especially in deep-seated and embedded engineering structures. This paper presents the bending response of piles installed through liquefiable layers located at depths beyond 20 m, and parametric analysis was conducted for a wide range of liquefiable layer thicknesses and depths by using OpenSeesPL (version 3.0.2) software. The numerical results were evaluated considering the inelastic concrete pile behavior under different earthquake records and different peak ground accelerations. The findings show that liquefaction can lead to a failure of piles even at depths greater than 20 m, and thus, a design consideration of piles may require a more comprehensive view considering the liquefiable layer depth and thickness effect. [ABSTRACT FROM AUTHOR]

Piles are walls that are installed underneath hydraulic structures to control seepage flow, uplift pressure, and exit hydraulic gradient. In this study, the effect of the ratio of width of the apron to the foundation depth (B/D), the ratio of the width of the apron to the downstream pile depth (B/d2), and the ratio of the upstream and downstream pile depths (d1/d2) on seepage flow characteristics is numerically investigated using the finite-element method. From the numerical simulations, design charts, and explicit formulas for estimating seepage flow characteristics, such as the percentage residual uplift pressure at key points, the discharge flow factor, and the exit hydraulic gradient factor underneath aprons with end double-piles for both states of equal and unequal depths are developed. The simulations are validated with existing analytical solutions for simple cases. To assess the accuracy of the presented formulas, statistical metrics; that is, the determination coefficient, root mean square error, and percent relative error (RE%) were used. The statistical metrics are satisfactory, and their values quantified the reliability of the proposed formulas. The proposed explicit formulas, with RE% less than 5%, could be used by design engineers instead of implicit analytical equations that involve elliptic integrals. [ABSTRACT FROM AUTHOR]

To investigate the responses of inclined loaded piles in layered foundations, this paper proposes a generalized solution based on the principle of minimum potential energy. First, the energy equations for an inclined loaded pile and the surrounding soil are deduced. With the consideration of deformation compatibility and the pile–soil interaction, the governing differential equation for the pile is obtained via a power series method based on the energy method. Subsequently, the power series solutions for the pile deformation under axial and lateral loads are obtained. The results indicate that the analytical solution proposed in this study can provide consistent predictions with experimental results. Furthermore, the ratio of the elastic modulus between the upper and the lower soil, the length–diameter ratio, and the change ratio of the elastic modulus of the adjacent soil have significant influence on the lateral displacement and the bending moment of the inclined loaded pile. [ABSTRACT FROM AUTHOR]

In this study, the free and forced vibration analyses of tapered piles subjected to axial harmonic loads were carried out. The first part of the paper presents the free vibration analysis of the tapered piles using an energy-based Rayleigh–Ritz method. The undamped natural frequency of the soil–pile system was obtained, and the results were validated using two analytical methods and a field test result reported in the literature. In the second part of the paper, the forced vibration analysis of tapered piles under vertical vibrations is carried out. Employing the Euler–Lagrange equation and calculus of variations, the governing differential equation for tapered piles under axial harmonic loading was obtained. A Taylor series expansion-based numerical technique called the differential transform method was used to solve the obtained differential equation. The numerical results were validated using reported full-scale forced vibration tests of cylindrical piles. The effects of the end fixities, slenderness ratio, the taper angle, and the degree of anisotropy on the response characteristics of tapered piles were discussed. [ABSTRACT FROM AUTHOR]

An analytical method will be proposed to investigate the bearing mechanism of piles in an anisotropic discontinuous rock mass. Based on the characteristic line method, the discontinuous part of the rock is considered as the boundary condition of the plastified zone, and Riemann's invariant governing equation will be applied at the boundary conditions to link these boundaries. It was found that four different failure mechanisms exist that depend on the inclination angle of weakness planes (χ): (1) conditioned by the planes of weakness in the intermediate zone (MC), (2) conditioned by the planes of weakness close to Boundary 2 in the active zone (M2), (3) conditioned by the planes of weakness close to Boundary 1 in the passive zone (M1), and (4) not conditioned by the planes of weakness (MI). Each pile failure mechanism contains four failure modes under different pile embedment and geostatic loads: (1) deep pile with minor overburden (DL), (2) deep pile and large overburden (DH), (3) semideep pile and small overburden (SL), and (4) semideep pile and large overburden (SH). Therefore, 16 pile failure modes exist and are distinguished by χ and the embedment ratios (n). The friction angles of the weakness planes (φ) have significant effects on the pile failure mechanisms. Under the failure mechanism of MC, M2, and M1, the peak of the percentage of pile bearing capacity in anisotropic discontinuous rock over that in isotropic continuous rock (NβP,DL/NβP,MI) increased with φ. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present simplified methods for determining the three-dimensional (3D) system capacities of pile foundations based on the lower and upper bound theorems of plasticity. The failure surface for a typical long offshore pile subjected to 3D head loads is derived based on the lower bound (LB) theorem of plasticity, and the LB capacity of a pile system is then proposed. Using the failure mechanism determined from the elastic solution in the LB analysis of a pile system, the upper bound (UB) capacity of the pile system is obtained from the energy-balancing equation. An actual offshore platform is selected as a case study to demonstrate the proposed methods. The current methods extend the planar limit analysis by incorporating global torsion and out-of-plane failures and can be useful in designing and assessing pile systems. [ABSTRACT FROM AUTHOR]

In pile construction, conventional pile materials such as concrete, steel, and wood are frequently subject to soil–substructure interaction durability problems due to corrosion and deterioration. Fiber-reinforced polymers (FRPs) provide a potential alternative to eliminate the durability problems of conventional materials. This paper describes the results of an experimental study on the effect of the interface on the behavior of glass FRP (GFRP) piles jacked into dense sand under axial loads. The aim of this study is to introduce an innovative GFRP piles in cohesionless soil through coating its surface with silica sand to enhance the pile interface behavior. The experimental program investigates seven small-scale GFRP piles with different surface roughness and a reference steel pile used as a control. The surface of five of the seven GFRP piles was coated with silica sand, and the performance of the GFRP piles was compared with that of the control steel pile. The results of the pile load tests were analyzed by using three different commonly used methods to determine the ultimate pile load capacities. The results showed that the innovative mechanism of coating GFRP piles with silica sand enhanced the interface friction of the GFRP piles in sand under axial loads and increased the ultimate pile load capacity in comparison with that of the control piles. [ABSTRACT FROM AUTHOR]

In this study, a numerical model is developed to study concrete-filled FRP tube (CFFT) pile behavior and interactions with foundation soil under lateral loading. The model, based on nonlinear finite element analysis (NFEA) and the disturbed state concept (DSC), considers material and geometrical nonlinearity as well as the interface of soil with fiber-reinforced polymer (FRP). Furthermore, the structural and geotechnical performance of the interface of soil and CFFT pile is studied by utilizing 3D finite element models (FEMs) of full-scale field tests conducted during the construction of a highway bridge on Route 40 in Virginia. Based on deflection along the length of the pile, the model results are in good agreement with the experimental data. To investigate the effects of various parameters on the behavior of CFFT piles and local buckling, a parametric study was also performed on different geometrical and material properties, including the pile diameter to length ratio, FRP tube thickness, concrete strength, and soil properties. It was found that the surrounding soil and length to diameter ratio exerted the most noticeable influence, followed by concrete strength. The FRP thickness had the least impact on the results. [ABSTRACT FROM AUTHOR]

The cone penetration test (CPT) is used as a complementary approach for determining the bearing capacity of piles. Via direct CPT methods for pile capacity prediction, correlation coefficients smaller than unity are used to relate cone tip resistance and sleeve friction to pile toe and shaft capacities, respectively. For correlating CPT data to pile capacity, specific factors must be considered, such as diameter, penetration rate, partial embedment of pile toe into a hard layer, mechanism of plunging, failure zone, data processing, and stress–strain conditions. The aim of this paper is to investigate the role and significance of scale effects to establish a direct relation between CPT records and pile shaft capacity. A database has been compiled including 83 full-scale pile load tests and CPT records in order to calibrate and validate the proposed approach. The less-than-unity ratio of pile shaft capacity to cone sleeve friction (i.e., rs/fs) for most of the cases shows that shear stress in the soil surrounding the pile is smaller than in the soil around the cone. Therefore, the differences between pile and penetrometer penetration rate and geometry are considered as the major factors that cause lower shear strain in the soil around the pile. By considering the determinants, an analytical-practical procedure is proposed, from which the pile shaft capacity can be predicted using cone sleeve friction. This approach demonstrates better agreement with measured capacity by static loading test results (Rs) and less scatter than other current CPT methods, and it can be used as a complementary approach for determining pile shaft capacity. [ABSTRACT FROM AUTHOR]

In this study, a nonlinear one-dimensional consolidation equation in terms of excess pore pressure is developed by considering the effects of variable permeability and non-Darcian flow condition. Uncoupled analysis for the determination of mobilization of shaft resistance is performed using a nonlinear load-transfer method. Finite-difference technique is used to predict the dissipation of excess pore pressure and settlement of piles. The predicted results are compared with reported numerical and experimental results and are within an error of 67%. The consolidation behavior of Cordemais clay (exhibiting non-Darcian flow) in terms of dissipation of excess pore pressure and the subsidence of soil surface with time is studied. The development of downdrag and the distribution of shear stress around the shaft of endbearing and floating piles are also investigated. The dissipation of excess pore pressure is about 75 and 40% for double drainage and single drainage conditions, respectively, after 25 years of consolidation. The total downdrag is about 85 and 115 mm for end-bearing and floating piles, respectively, after 25 years of consolidation. [ABSTRACT FROM AUTHOR]

Particle breakage has a significant impact on the mechanical properties of soils and has drawn continuous concerns among researchers. This study aims to deepen the current understanding on the particle breakage phenomenon through insights of high frequency acoustic emission (AE) signals. Two series of physical model pile tests were performed with AE instrumentation, using two different materials: silica sand and coral sand. The AE signals were digitalized continuously throughout the tests with a sampling interval of 0.5 ms (2Mps), which enabled the signals with a maximum frequency of 1MHz to be captured, and the AE signals with a frequency higher than 100 kHz were interpreted to be associated with particle breakage mechanism. Results show that the high frequency AE (i.e., particle breakage) occurred throughout the tests. An initial period of rapid rising and a following period of relatively stable high frequency AE signals were observed in all tests. Based on AE characteristics, the extent of particle breakage was found to be related to thematerial property, the pile penetration depth, and the ground density. In general, silica sand was found to be more emissive, although coral sand was more prone to break, and the dense ground was more emissive and more prone to break than the loose ground. In conclusion, the asymptotic evolving trend is suggested for simplified estimation of particle breakage during the pile penetration process. [ABSTRACT FROM AUTHOR]

This paper presents the derivation of a generalized nonlinear softening load-transfer model to analyze the load-settlement response for a single pile subjected to axial loading. The model requires the calculation of a single parameter, n, so that the number of field trial tests can be reduced significantly compared with other empirical solutions with multiple parameters. Variations in n can provide approximations for different soil–pile interaction systems. The model explicitly considers both the hardening and degradation behavior of skin friction with shear displacement. The effectiveness of the proposed method was verified through comparison of the evaluations with field measurements and other analysis results. A hyperbolic load-settlement model of pile-point resistance was incorporated with the load-transfer function for skin friction to develop an efficient computer program for settlement analysis of axially loaded piles. A comparison was made between the current approach and other analyses. Satisfactory performance was obtained for the new calculation framework, where the estimated settlement differed within 13%. In this paper, the softening effect of load-settlement response of a pile is also illustrated in a worked example. [ABSTRACT FROM AUTHOR]

A series of pullout tests were conducted on a model pile in a soil with different initial water contents and different pile surface roughnesses to study their influences on pile skin friction. To measure axial strains and skin friction of the pile, fiber Bragg grating (FBG) strain sensors were used. Data were collected during the pullout tests and are analyzed in this paper. Test results indicate that the skin friction and axial strain of the model piles decrease with the initial water content of the soil but increase with the degree of surface roughness of the piles. The axial strain induced in the upper segment of the tested pile is considerably greater than that in the bottom segment of the pile. In addition, the skin friction is distributed nonlinearly along the length of the model piles. [ABSTRACT FROM AUTHOR]

In this study, the differential quadrature method (DQM), a mathematically simple, accurate, and computationally efficient numerical tool, was employed to analyze the response of single piles under dynamic axial loading. The dynamic behavior of the piles and surrounding soil were modeled using the one-dimensional (1D) or three-dimensional (3D) axisymmetric elasticity theory, respectively. The governing equations subjected to the related boundary and initial conditions were discretized in both the spatial and temporal domains via DQM. The behavior of the floating piles embedded in a half-space layer of homogeneous and Gibson soils under uniform and sinusoidal impact loads was studied. The piles and the soil behavior were assumed to be linear elastic and linear viscoelastic, respectively. To compare and verify the results obtained from the DQM approach, the problems were also solved via a finite-element-based commercial software program in some cases. The approach was found to have high accuracy and numerical stability. Finally, the effects of the different parameters of the soil and pile on the pile-head settlement time history were investigated. [ABSTRACT FROM AUTHOR]

In the case of large-diameter monopiles, pile deflection against lateral loads must be predicted accurately to determine the direct influence on the superstructure. One-dimensional (1D) linear models of the pile-soil system, which are simple to analyze, are more commonly used in practice than the sophisticated three-dimensional (3D) simulations. This study proposes an equivalent lateral strain concept to incorporate soil nonlinearity into an equivalent linear analysis of the pile-soil system. The spring constant is obtained by iterating over soil stiffness at different strain levels and finding equivalent lateral strain from updated pile deflection at each iteration. It requires the maximum shear modulus and modulus reduction curve for different layers of the soil profile. Correlation between the equivalent lateral strain and pile deflection has been developed by comparing results from 1D and 3D simulations of long piles. The existing correlations between the lateral spring constant and Young's modulus of soil are too approximate to help in quantifying nonlinearity of soil accurately in this comparative study. Therefore, a more accurate relationship between spring constant and Young's modulus of soil for long piles has been proposed by incorporating relative stiffness of soil and pile. [ABSTRACT FROM AUTHOR]

This paper presents the effect of surcharge support pressure on pile load-settlement response during static load testing. A three-dimensional nonlinear finite-element model is developed to investigate the loading sequences of an axial compressive static load test, using surcharge loads as the reaction system. Results of a static load test at a construction site for which the geotechnical data are available were used for verification of the numerical model. The results show that the surcharge pressure on supports has little impact on the ultimate capacity of the pile, as the shaft skin friction is slightly influenced by the surcharge and the effect on the tip resistance is negligibly small. The initial stiffness of the pile, however, might be considerably affected by the surcharge pressure distributed around the pile shaft. The influence on stiffness increases with increase in the pile diameter. The effect of surcharge pressure is more pronounced for piles embedded in frictional soils compared with cohesive soils. Comparing the results with those available in the literature for pile testing using the reaction pile system shows that the pile stiffness is 15 to 25% less affected in the surcharge reaction system. [ABSTRACT FROM AUTHOR]