Search

Under the combined action of environmental and seismic loadings, offshore wind turbines supported by tetrapod piled jacket (TPJ) foundations may experience tilting and rotational failures, and even the shutdown. However, there is still a notable gap in the research on the dynamic response of the TPJ system in this condition, especially in the multilayered clay deposits. This study conducts advanced three-dimensional finite element simulation to investigate the seismic response of TPJ systems in soft-over-stiff clay deposit under the combined influence of wind and wave loadings. The results indicate that with a minor strength ratio between two layers, especially for strength ratios < 0.28, the peak values of the pile bending moment envelopes increases obviously, which is located near the soil layer interface. Near the soil layer interface, a sudden expansion in the soil plastic strain can be observed at this location. When the top layer thickness is substantial, surpassing 0.75 times the pile length, the restraining effect of the bottom stiff layer on the pile results in the peak value of the acceleration response envelopes and a significant reduction in bending moment near the pile end. [ABSTRACT FROM AUTHOR]

Single-point mooring (SPM) system has been used in offshore engineering for its superiority in overcoming severe sea conditions. However, researches focused on the interaction mechanism between the anchor pile and soil in SPM systems remains insufficient, especially regarding the calculation method for oblique pullout bearing capacity that considers padeye depth. Based on the p-y curve method and load transfer method, this paper presents a simple prediction method for the behavior of anchor piles embedded in sand under oblique pullout load. The theoretical predictions are validated through comparing with results from the three-dimensional finite element method and existing centrifuge model tests. The effect of the loading angle and the padeye depth are analyzed and discussed. A negative bending moment peak and axial force discontinuity phenomenon appear at the padeye depth. The optimal padeye depth for anchor piles in this study ranges from approximately 0.53 to 0.80 times the pile length. When the padeye depth is less than 0.33 times of the pile length, the ultimate bearing capacity of the anchor pile increases with increasing load angles. Conversely, when the padeye depth exceeds 0.33 times the pile length, the ultimate bearing capacity decreases with the increasing load angles. [ABSTRACT FROM AUTHOR]

This research developed a robust Bayesian framework for evaluating geomaterials and soil-structure interactions involving deep excavation, utilizing Bayesian Regression and Bayesian Network methods that combined data training, validation, and updating into a cohesive framework. A methodology based on Bayesian Generalized Linear Model (a variant of Bayesian Regression) was applied to a laboratory-based case study on sustainable cementitious blends. The framework effectively used past research data to estimate design parameters even though the studies involved different mix design requirements. Then, a framework based on Gaussian Bayesian Network (a variant of Bayesian Network) incorporating Bayesian updating was applied to an established case history for deep excavation in clay. Two-dimensional finite element analysis was used to generate data for model training and updating. The GBN models accurately estimated responses such as wall deflections, wall bending moments, and ground surface settlements through a sequential updating process. The research was conducted using R programming language, with a custom R script designed to follow the process flow of the proposed framework. The successful application and validation of this framework demonstrated its potential for characterizing geomaterials and evaluating complex soil-structure interactions in deep excavation, leveraging on the availability of existing data and a reliable sequential updating process. [ABSTRACT FROM AUTHOR]

This paper aims to systematically describe the mesostructural and mechanical changes in the surrounding soil of glass fiber-reinforced polymer–trapezoidal core sandwich piles (GFRP-TCSPs) under lateral loads. A lateral loading device for hydraulic gradient testing is introduced, and a corresponding numerical model is established using a continuum-discrete coupling method. The dynamic interaction between the GFRP-TCSP and the soil during incremental loading is analyzed, including the effect of the soil particle contact parameters on the pile–soil interaction (PSI), changes in the pile bending moment, and the displacement field of the surrounding soil. The development of soil force chains and changes in porosity and coordination number in different zones of the soil around the pile are investigated. The results indicate that the attraction and friction between particles are crucial for the PSI behavior of the soil. In addition, the bending moment of the pile increases with increasing lateral load but decreases when the pile inclination angle diverges significantly. Different regions of the soil around the pile exhibit different variations in average contact force, porosity, and coordination number as the GFRP-TCSP overturns. These variations provide a theoretical basis for detecting pile instability. [ABSTRACT FROM AUTHOR]

While the effects of tunnel construction on vertical loaded piled foundations have been extensively explored, the impact of side-by-side twin tunnel excavation on laterally loaded pile groups remains less understood in existing literature. This study investigates the repercussions of twin tunnel excavation at various depths on a laterally loaded (2 × 2) pile group, utilizing a combination of three-dimensional centrifuge model tests and back-analyses employing a sophisticated hypoplastic model. The test IDs CD1.5_1.5, CD2.7_2.7, and CD3.7_3.7 represent tunnelling activities near the pile shaft, pile toe, and beneath the pile toe in a side-by-side twin configuration. Twin tunnelling in test CD1.5_1.5 resulted in the most significant lateral movement of the pile cap due to reduced horizontal stress near the pile group shaft. Furthermore, twin tunnelling in test CD2.7_2.7 led to a substantial transverse tilt of 0.5 % for the pile cap, surpassing the recommended 0.2 % limit per Eurocode 7. During the second tunnelling in tests CD2.7_2.7, and CD3.7_3.7, a shift in load direction from upward to downward occurred in pile P2, potentially compromising its integrity. In test CD1.5_1.5, stress reduction near the pile shaft led to pile P1 enduring a bending moment of 1050 kNm at its midpoint, exceeding its capacity of 850 kNm. [ABSTRACT FROM AUTHOR]

Multiple fault planes often coexist within a fault zone during fault dislocation. However, all the previous analytical models assume that there is only one fault plane during a fault dislocation, which is inconsistent with the actual engineering conditions. In this paper, theoretical analysis and numerical simulations are used to investigate the mechanical response and damage characteristics of tunnels subjected to multiple normal faulting. A nonlinear theoretical model is established for analyzing the mechanical response of tunnels subjected to multiple normal faulting. The number of fault planes, the shear effect of the soil and the tunnel, the fault zone width, and the nonlinear soil−tunnel interaction are applied inside the theoretical model, significantly improving the analysis accuracy and applied range. The corresponding numerical simulation based on the Concrete Damaged Plasticity (CDP) Model is carried out to study the damage characteristics of the tunnel. The proposed theoretical model is verified by model tests and numerical simulations, which exhibit consistency in both qualitative and quantitative aspects. A parametric analysis is presented, wherein the impacts of varying numbers of fault planes, fault plane distances (d), fault displacement ratios (ξ), and buried depths (C) on the tunnel response are investigated. The results show that an increasing number of fault planes leads to a reduced peak bending moment (M max) and shear force (V max). As the number of fault planes increased from one to four, M max and V max decreased by 1.57 times and 3.31 times, respectively. Expanding d corresponds to a reduction in both M max and V max. The minimum V max within the tunnel materializes at ξ 4 (Δf d1 = Δf d2 = Δf d3), and the tunnel's V max appears at the fault plane of maximum fault displacement. Moreover, with the augmentation of C , an increase in both M max and V max was observed. Additionally, upon attaining a normal fault displacement of 0.2 m, the tunnel lining undergoes both tensile and compressive failure at the fault plane. As the normal fault displacement surpasses 0.4 m, the failure range of the tunnel at the fault plane undergoes a precipitous escalation, marked by a maximum increase of 68.8 % in tensile failure and a 29.6 % increase in compressive failure. [ABSTRACT FROM AUTHOR]

This study presents the impact of tunnelling on a battered and vertical pile groups when subjected to lateral loads. A comprehensive investigation was undertaken to examine the effects of varying the tunnel depth in relation to the length of the pile group, as well as the direction of the lateral load (i.e., towards and away from the tunnel). A sophisticated hypoplastic model, which has the ability to accurately represent the small strains stiffness was used to capture clay behaviour. As compared to the battered pile group, the vertical pile group exhibited the largest pile cap lateral displacement due to tunnelling adjacent to pile shaft. The tunnel below the battered pile group toe exhibited the most significant pile cap lateral displacement and tilting of the pile group. The stress release caused by tunnelling in the vicinity of the pile shaft induced the largest bending moment in both battered and vertical pile groups, regardless of direction of the applied lateral load. The pile cap experiences linearly increasing lateral movement with tunnel volume loss. Moreover, the lateral movement and tilting are greater in the presence of lateral loads compared to vertical loads on the battered pile group. [ABSTRACT FROM AUTHOR]

Offshore wind turbines (OWTs) are affected by wind, wave, and current during their service life, which lead to the substructures undergoing combined effects of complex lateral loads and local scour. This phenomenon poses a significant challenge to the bearing capacity and cyclic responses of the widely used rigid monopiles for OWTs. This study develops three-dimensional numerical model to investigate the behavior of a rigid monopile subjected to lateral monotonic and cyclic loads, considering the stress history alteration induced by local scour. The hysteresis and plasticity accumulation of soils are captured by a bounding surface model. An accurate and concise semi-implicit stress integration scheme is creatively proposed to effectively incorporate this advanced constitutive model into the finite element (FE) software. The numerical model is verified by comparing FE results with centrifuge test results. Subsequently, the key factors such as cumulative deformation characteristics and bending moments distribution are investigated under different scour and cyclic loading conditions. The results indicate that with the facilitation of proposed semi-implicit scheme, the bounding surface model is capable of capturing the deformation pattern and cumulative deformation behavior of laterally loaded rigid monopile, and the cyclic responses of the monopile are significantly affected by the local scour. [ABSTRACT FROM AUTHOR]

In recent years, massive interbedded sandstone and slate anti-dip slopes have been discovered in the southwest and northwest regions of China. The distinct mechanical properties of different rock layers make these slopes particularly unique. In this paper, the finite-discrete element method (FDEM) is used to study the toppling failure mechanism of soft-hard interbedded anti-dip rock slopes (SHIADRSs). Firstly, the numerical model of soft-hard interbedded anti-dip rock slope (SHIADRS) is established based on a centrifugal loading test. Then, the stress state, evolution of displacement and cracks, and progress of toppling failure in the SHIADRS are analyzed. Besides, the effect of rock structure, slope angle, dip angle, and rock mechanical properties on the toppling failure of SHIADRS is discussed. The simulation results show that the toppling failure process of SHIADRS can be divided into three stages. The stress distribution in hard rock (HR) is obviously different from that in soft rock (SR) layers. HR layers bear greater bending moments than HR layer during the toppling failure of the soft-hard interbedded anti-dip rock slopes. In addition, the stability of SHIADRS is negatively correlated with the slope angle and the dip angle of rock layer. Compared to the inclination angle of rock layers, the slope angle has a more significant impact on the stability of slopes. The internal friction angle of the rock layer has almost no effect on the toppling failure of SHIADRS. [ABSTRACT FROM AUTHOR]

Immersed tunnels typically pass through zones with different soil properties and may be subjected to earthquake threats. This paper presents a theoretical model using two flexible joints and three tube-elements for the longitudinal seismic response analysis of immersed tunnel connecting artificial islands. According to the reaction displacement method, the governing equations for bending of the immersed tunnel are established. Based on the matrix transfer principle, the end boundary conditions and the joint continuity conditions were considered in the analytical model. The analytical solutions were verified using finite element simulation results. Results indicate that the fixed and hinged end conditions have large shear forces on both ends, while the fixed end conditions have large bending moments. The free and roller end conditions have large vertical displacements on both ends, while the hinged end conditions have large rotation angles. The free end conditions can better reflect the boundary conditions of immersed tunnel connecting artificial islands. The flexible element joints can significantly reduce the shear forces at the interface of different strata, but also produce larger deformations at the joints. However, this amount of deformations can be accommodated by the flexible joints themselves, thus minimizing the damage to the immersed tunnel under seismic loading. [ABSTRACT FROM AUTHOR]

Numerical simulation models for pile group-superstructure in liquefiable and non-liquefiable sites were established. The validity and reliability of the numerical model are verified by the shaking table test results. Based on the cross-correlation analysis of superstructure acceleration-pile bending moment and soil displacement-pile bending moment obtained from the tests, the coupling law of kinematic and inertial interaction and its influence on pile failure modes were discussed combined with the numerical simulation results. The results shown that the effect of kinematic interaction on piles were greater than that of inertial interaction in both types of sites, but coupling mechanisms of kinematic and inertial interaction were different. For the liquefiable site scenario, the middle part of piles was prone to bending failure and the kinematic interaction was the main reason for it. For the non-liquefiable site scenario, the inertial interaction had an obvious influence on the pile failure occurred at the pile top. The results of parameter analysis shown that the mass of the superstructure was the most important parameter of inertial interaction in the liquefiable site. Parameters of inertial interaction would affect the vibration of the superstructure in the non-liquefiable site, but the influence on pile bending moments was not obvious. [ABSTRACT FROM AUTHOR]

This paper presents a novel mechanical model for seismic response analysis of vertical shafts. The model is based on elastic foundation beam theory and simplifies the shaft linings as parallel Euler Bernoulli beams. Their interaction is simulated using uniformly distributed springs. The governing differential equation for shaft vibration is derived for SH wave excitation. The seismic input motion is applied to the primary lining by converting the free field displacement into harmonic form. The closed-form solutions for seismic response of both primary and secondary linings are obtained via the transfer function method. The accuracy of analytical solution is validated by comparing with finite element analysis results. Additionally, the impact of foundation stiffness, secondary lining thickness, shaft outer diameter, and relative stiffness between linings on seismic response are investigated in the parametric analysis. The analytical solutions of the seismic response analysis of vertical shafts indicates that the relative stiffness between linings significantly affects the secondary lining's peak bending moment. Furthermore, higher stiffness of the elastic connection layer between the two linings can effectively reduce the peak displacement response of the secondary lining. [ABSTRACT FROM AUTHOR]

Mountain tunnels buried in squeezing soft rock inevitably undergo a rapid degradation with time due to creep behaviors of surrounding rock. The performance of tunnel would become more exacerbated when steel corrosion occurs in lining structures. High failure risk of tunnel lining within a short time after construction would significantly shorten its service life. Since the properties of rock mass in space and the corrosion of reinforcements in space–time exhibit a high uncertainty in practices, it is necessary to perform a reliable performance assessment of tunnels by incorporating the concept of random field-based reliability analysis. In this study, a novel approach for reliability assessment of mountain tunnels under the hazards associated with creep behavior and non-uniform steel corrosion is presented. A creep constitutive model of rock is introduced firstly; Random field-based modeling for the spatial-variant properties of rock mass is proposed; and a spatio-temporal approach for describing the spatial variability and stochastic process of steel corrosion is established. Numerical simulation for the deteriorated mountain tunnel is implemented by integrating the FLAC3D with MATLAB. In an illustrative example, both deterministic and probabilistic analysis on structural performance were conducted. The time-dependent deformation, axial forces and bending moments of lining structure are investigated. [ABSTRACT FROM AUTHOR]

In this study, the structural response of piles during shield machine cutting is analyzed using p-y curves based on the finite element method (FEM). In the FEM program, the tangent stiffness matrix of the nonlinear soil-pile spring is derived from the tangent modulus of the p-y curve. The nonlinear finite element equation is solved using the Newton-Raphson iterative method. The program can consider the influence of the shield thrust force, the soil reinforcement, and the cross-sectional area decrease during shield cutting. The program output comprises the lateral displacement, internal force, and bending moment of the laterally loaded monopile. The correctness and accuracy of this method are validated with both field test data and commercial finite difference method (FDM) program. The results show that shield thrust force is the main factor affecting the lateral displacement and bending moment of the pile; as the cutting section area of the pile is decreasing, the maximum negative moment increases while the maximum positive moment decreases; soil reinforcement has a negligible effect on the internal force but can effectively reduce the lateral displacement of the pile head. [ABSTRACT FROM AUTHOR]

An analytical approach is presented for predicting the response of the pile by lateral soil movement in a model test in terms of the two-stage procedure. The prescribed lateral soil movements with inverse triangular, uniform, and arched profiles are examined in the analysis. The free-field displacement is obtained explicitly by the elasticity and Fourier expansion technique. The soil–pile interaction is considered for the response of the pile under soil movement in light of the theory of a beam on the Winkler foundation. Parametric studies are performed to investigate the effects of the soil–pile system and the loading conditions on the response of the pile. The free-field displacement attenuates quickly with its distance to the loading block. The pile response under lateral soil movement in the model test is greatly dependent on the pile location and the loading conditions. For the pile with a free tip, the deflection and bending moment of the shaft are relative to the restraint condition at the top. The effect of the pile-soil stiffness ratio is not great on the deflection of the pile but significant on the bending moment of the shaft. [ABSTRACT FROM AUTHOR]

This paper describes research on the behavior of anchored sheet pile quay stabilized by deep cement mixing (DCM) columns in soft soil through a centrifugal test investigation to understand excavation-induced soil-structure interaction mechanisms. By employing an advanced soil constitutive model, three-dimensional (3-D) finite element (FE) simulations were subsequently performed to back-analyze the centrifuge test. Moreover, a numerical comparison analysis between this case and a null DCM columns case was performed to describe the shielding effect of the DCM columns composite foundation in the anchored sheet pile quay in terms of lateral earth pressure, bending moment, lateral deflection of the quay wall, and quay ground settlement induced by excavation. Finally, a parametric study was carried out to investigate the effect of DCM column arrangement and geometry on the quay wall lateral deflection. Results showed that the presence of DCM columns reduced the adverse effects on the quay wall in excavations, and they could effectively enhance the stability of the anchored sheet pile quay in soft soil, such as the shielding effect. In addition, the parametric study results indicate that length and the elastic modulus of the column are two critical factors affecting the shielding effect of DCM columns. This research provides reasonable explanations and valuable insights to understand the soil-structure interaction mechanism in anchored sheet pile quay and is of use in the preliminary design of sheet pile quay structures in soft soil. [ABSTRACT FROM AUTHOR]

Abstract Numerical modelling using Plaxis-2D is carried out to study seepage forces on suspended type cutoff walls in highly permeable soils. On increasing differential pressure head, deformation and bending moment in cutoff walls increased. On increasing the differential pressure, the point of occurrence of maximum deformation and maximum Bending Moment in downstream cutoff wall shifts upwards but in upstream cutoff wall, shifts downward. On increasing relative density and soil modulus, the deformation and bending moments reduced. For changes in pressure head, relative density and soil modulus, the deformation and bending moment are always higher in downstream cutoff wall than upstream wall. [ABSTRACT FROM AUTHOR]

The mechanism of bending failure and the magnitude of the bending moment in a column formed by cement deep mixing (CDM) under an embankment load were investigated by a series of three-dimensional (3D) finite element analyses. Based on the numerical results, a design method to consider the bending failure of the CDM column has been established. The usefulness of the proposed methods was verified using the results of two centrifuge model tests of the embankments on the CDM column improved soft model ground model reported in the literature, and the columns had tensile cracks or showed complete failure. [ABSTRACT FROM AUTHOR]

Inverse analysis procedures are used to update project parameters and applied to predict future performance in the later stages. However, the inverse analysis procedure of earth pressure of excavation has received less attention. This paper proposes an improved inverse analysis method and the modified apparent earth pressure model for braced excavations in soft clay. A new procedure for inverse analysis of excavation is suggested based on the quintic spline interpolation function, and a trial algorithm is used to eliminate the errors generated in the inverse process. The proposed inverse solutions are validated by numerical simulations and reported engineering examples and show good agreements. Based on the inverse data and empirical apparent pressure diagram (APD), a modified apparent earth pressure method for braced excavations in soft clay is further suggested. And the relationship between the degree of anisotropy of soft clay and apparent earth pressure coefficients is discussed. The study results provide a reference for dynamic feedback design and adaptive management of the excavation. [ABSTRACT FROM AUTHOR]

The structural assessment of segmental grey cast iron (GCI) tunnel linings to nearby construction is challenging due to the presence of the joints affecting the stiffness of the tunnel lining. This paper presents an extensive investigation, using 3D finite element (FE) analyses, into the bending moment-rotation (M-θ) behaviour of two GCI tunnel joint geometries. These two geometries correspond to standard running and station tunnels of the London Underground network. The contribution of this study is two-fold. i) The novel characterisation of the M-θ response enables the development of new models for simulating the mechanical response of GCI tunnel joints with structural elements which can be used in simplified, 2D geotechnical analysis for tunnel safety assessments. ii) The analyses provide insight into the behaviour of GCI tunnel linings that would be difficult to achieve through experimental and field observations alone. More specifically, the analyses show that when the bolts are removed from the joints the possibility of tensile failure can be disregarded; that the initial bolt preload influences the rotational stiffness only after some rotation has taken place and does not alter the bending moment of opening; and that the out-of-plane displacement restraint has little influence on the joint response. [ABSTRACT FROM AUTHOR]

Bridge foundations located in a water flow environment commonly experience scour, which can lead to significant drops in the soil elevation immediately surrounding the foundation. This has significant ramifications for lateral bearing capacity as well as the integrity of the supported superstructure. While pile groups are one of the most foundation systems for bridges, current research on scouring effects has been largely limited to single piles. This paper fills this gap through the use of 3D finite element (FE) analysis, validated using centrifuge tests reported elsewhere in the literature. Results from a parametric analysis is described exploring the effects of the scour hole geometry, defined by the depth and slope angle, on the lateral behavior of pile groups. In particular, the influences on the load–displacement and bending moment and soil resistance distributions with depth for each pile within the group are considered. The results show that scour can have a significant detrimental influence on the lateral response of a pile group. An increase in the length of the pile group is also shown to significantly reduce the sensitivity of the lateral bearing capacity of the group to scour. [ABSTRACT FROM AUTHOR]

This study aims to analysis the longitudinal seismic responses of circular tunnels across soil-rock stratum longitudinally ("soil-rock" means two different stratums, not just the soil and rock ground). Based on an improved elastic foundation beam model, an analytical solution is derived to investigate the seismic response of long tunnels across soil-rock stratum, subjected to sinusoidal shear motions. The improved elastic foundation beam model adopts the Timoshenko beam and Winkler foundation, with considering tangential contact conditions at the ground-tunnel interface. The free field reaction considers the reflection and transmission by the soil-rock interface and the wave passage effect. Explicit formulations are obtained for tunnel displacement, rotation angles, bending moments and shearing forces. The proposed solution is verified by comparing with the dynamic numerical results, as well as traditional analytical solutions. Finally, a parametric study is conducted to investigate the influence of traveling wave effect, earthquake frequency, shear wave velocity ratio of two stratums, lining stiffness and contact condition on tunnel seismic responses. The proposed analytical solutions can be used to predict the longitudinal seismic response of deep circular tunnels crossing soil-rock stratum in engineering design. [ABSTRACT FROM AUTHOR]

Adjacent excavations may have adverse impacts on the existing tunnels. Due to the increasing demand for building excavations in close proximity to existing metro tunnels, ensuring the safety and integrity of tunnel structures is a major challenge for city designers and geotechnical engineers. Urban metro tunnels in soft areas of Chinese cities are often constructed using shield tunnelling technology, and the installed precast reinforcement concrete segmental lining are generally connected together by various steel bolts. Due to the presence of joints, the overall tunnel stiffness, including the bending stiffness and shearing stiffness, are significantly reduced. Due to the reduction in shearing stiffness, the tunnel longitudinal deformation can be decomposed into two distinct modes: a bending mode and a shearing dislocation mode. However, current methods for predicting tunnel longitudinal responses to adjacent excavations generally simplify a tunnel as an Euler-Bernoulli beam, which only considers the bending effect and ignores the shearing deformation of jointed tunnels. Moreover, tunnel-ground interactions are commonly considered through the Winkler foundation model, which is unable to account for the interactions of adjacent springs and leads to overestimations of shear forces and bending moments in shield tunnels. In this paper, a new analytical method is proposed that uses a Timoshenko beam to simulate jointed shield tunnel responses when subjected to an adjacent excavation, which can consider both the bending and shearing effects of a shield tunnel. The tunnel-ground interaction is considered by introducing Pasternak two-parameter foundation, which is able to further take account for the interaction between adjacent springs. The tunnel-excavation interaction is analyzed using a two-stage analysis method. First, the excavation-induced unloading stress on the existing tunnel is computed using Mindlin’s solution. Second, the tunnel longitudinal deformation due to the corresponding stress is calculated using finite difference method. The effectiveness of the proposed approach is validated by two well-document case histories, including finite element analysis and field measurement. The predicted results are also compared with those obtained using the traditional methods. Based on the verified analytical solution, a parametric analysis is also conducted to investigate the effects of key factors on the responses of existing tunnels, including excavation-tunnel relative position, ground Young’s modulus and equivalent shearing stiffness. [ABSTRACT FROM AUTHOR]

Chalk's sensitive, variable nature poses difficulties for foundation designers. It can present as weak rock and yet be de-structured to very weak putty by dynamic or high-pressure loading. The development of multiple offshore wind farms at north European chalk sites led to the recent ALPACA Joint Industry Programme, which undertook intensive material characterisation and large-scale field testing at St Nicholas at Wade (SNW), Kent, UK to capture and better understand the behaviour of piles driven in fractured low-to-medium density chalk. Noting that lateral loading response is a vital design concern for monopile and jacket supported structures, this paper focuses on 3D Finite Element (FE) modelling of ALPACA's monotonic lateral loading field tests on open-ended driven tubular steel piles. The brittle chalk is modelled with a strain-softening Mohr-Coulomb model combined with nonlocal regularisation, calibrated meticulously against the ALPACA characterisation dataset. A second, simpler modelling approach, adopting a perfectly-plastic Mohr-Coulomb model, is also explored as a simplified practical alternative. Both approaches can match field lateral capacity and bending moment distributions, after taking due account of pile installation and chalk fracturing effects. The analyses indicate how robust, accurate and cost-effective lateral loading design may be approached for low-to-medium density fractured chalks. [ABSTRACT FROM AUTHOR]

The safe and stable operation of monopile offshore wind turbines (MOWTs) under seismic and environmental loading is a major challenge facing designers. A numerical method was developed for simulating the dynamic interaction of the soil-pile-structure system by employing an elastoplastic bounding surface constitutive model that can capture the cyclic degradation of clay stiffness well. Then, the suitability of the method was validated by comparison with the existing simulation results in the literature. The dynamic responses of MOWTs to seismic and environmental loading were simulated by employing the above numerical method. The effects of soil plasticity and stiffness degradation on the dynamic responses of MOWTs were investigated. The influence of environmental loads on the seismic responses of MOWTs was also analysed. It was found that the monopile experienced significant rotation and settlement, and the soil plasticity and stiffness degradation significantly increased the peak response of the lateral deflection, rotation angle and bending moment of the MOWT under combined seismic and environmental loads. The input bedrock peak acceleration was amplified to varying degrees from the monopile bottom to the tower top, and the acceleration amplification along the height was the most significant overall when considering the soil stiffness degradation. Environmental loads such as winds and waves significantly increased the absolute values of the seismic response profile, including the deflection, rotation angle and bending moment, as well as the acceleration amplification factor. The research results can support the seismic design of MOWTs. [ABSTRACT FROM AUTHOR]

This paper presents an analytical method to predict the horizontal capacity of piles in unsaturated soils. The method extends the well-known Broms approach to account for the combined effect of the groundwater table and the apparent cohesion of the unsaturated soil above it. Similar to the original formulation of Broms, the present method calculates the maximum horizontal force and bending moment that can be sustained by the pile for two different head fixities (i.e. free-head and restrained-head) as a function of non-dimensional parameters that depend on the geometry and flexural resistance of the pile (i.e. yielding moment), the soil resistance and the type of failure mechanism (i.e. short, intermediate or long pile). Compared to Broms' solution, the method introduces additional non-dimensional parameters that relate the water retention behaviour of the soil to the geometry of the pile. The proposed formulation accurately predicts the lateral capacity of piles as experimentally measured in previous works. Results confirm that consideration of the partially saturated state of the soil above the groundwater table is essential for a reliable estimate of the horizontal capacity of piles. [ABSTRACT FROM AUTHOR]

In this paper, a new corrugated core sandwich wall (CCSW) made of pultruded glass fiber-reinforced polymer (GFRP) composites was proposed to address the threat of flood damage to levees overtopping. The critical hydraulic pressure for the instability of the CCSW under stepped hydraulic loading was determined with a continuum-discrete coupling method, and the dynamic wall–soil action of the CCSW at a protection height and penetration depth ratio of 1:1 was analyzed. Finally, under the critical hydrostatic pressure of instability, the influence of the dimensions of the CCSW on its deflection were analyzed, and a cost-effective section was determined using economic rationality analysis. During the overturning process of the CCSW, the bending moment of the wall increased, the soil force chain changed from vertical to lateral, and the main force of the downstream soil on the wall moved downward, which explained the downward movement of the maximum bending moment of the wall from a mesoscopic viewpoint. The deflection of the CCSW increased with decreasing skin thickness, core layer thickness and core height, and an increase in skin thickness could reduce the deflection of the CCSW more effectively than that in the core layer thickness. [ABSTRACT FROM AUTHOR]

Based on advanced clay-monopile-OWT numerical model, the wind-wave coupling effect was investigated. Compared to the case of wind load only, both the nacelle top displacement and the maximum monopile's bending moment are smaller when the wind-wave load coupling is considered. The monopile-head displacement cumulation can cause the drift of the nacelle top displacements. Moreover, the wind and wave loads may cause opposite accumulative direction of the monopile-head displacement due to the difference in load nature. The displacement cumulative magnitude is positively correlated to the load magnitude. Hence, the monopile possesses better energy-dissipating capacity in the coupled load case. The equivalent damping ratio of the soil is about 3.2 ∼ 4.9% under the wind-wave combination, 1.2 ∼ 1.4% under the wind only and 2.3 ∼ 3.5% under the wave only, which agrees with superposition principle. Under the wind-wave loads, noticeable accumulation of excess pore pressure exists in the seabed soil. Compared to the separate load cases, the excess pore pressure in the coupling case may be smaller. Analysis also showed that mean effective stress of soil decreases with loading time due to pore pressure buildup, although the soil mean stress may increase when total stress method is considered. [ABSTRACT FROM AUTHOR]

This paper investigates the response of pile foundations to deep-excavations. An elastoplastic two-stage model is used to study the response of pile groups (with free- or rigidly capped-heads) and of piled structures (grade beams or bearing walls), considering piles embedded in either uniform or layered ground. The model is validated using results of analytical solutions, as well as data from centrifuge tests and from real case histories. Then, a parametric study investigates excavation-induced displacements and internal forces of piles, and deformations of the superstructure. Soil–pile transfer mechanisms and pile–superstructure interactions are analysed for various foundations and ground conditions, with results showing that settlements and slopes between piles are larger for floating piles than for end-bearing piles. Results show that rigidly capped piles and semi-flexible piled structures cause bending moments at the foundation heads that increase with the excavation-induced slope between piles, whereas the risk for tensile failure of piles is low. Also, results indicate that the superstructure stiffness is more relevant to decrease the slope and deflection ratio of foundations when composed of floating piles, compared to end-bearing piles. Finally, modelling end-bearing piles embedded in a stiff base using hinged connections to such stiff base may not be appropriate. [ABSTRACT FROM AUTHOR]

A simplified method validated by centrifuge tests is developed to estimate both the deformation and stability of soft ground improved by piles during the rapid construction of embankments. Furthermore, this method, which considers pile-soil interaction, is adopted to investigate the failure mechanism and performance of piles. It is determined that piles embedded in a stiff stratum may be subjected to a dual bending failure. The first failure may occur at the soft-stiff interface because of the embedment effect of the stiff stratum, while the second failure may take place at the upper part of the piles due to the inflexion effect of soft ground movements. A progressive bending failure of piles may also occur as the maximum bending moment of each pile varies with the pile location. The progressive failure could propagate from the piles beneath the embankment toe towards the embankment centre. In addition, the location, stiffness, and fixity of piles have a significant influence on the stability of soft ground. The piles beneath the embankment toe are key piles, and increasing the stiffness and enhancing the embedment of these piles could efficiently ensure the stability of soft ground. [ABSTRACT FROM AUTHOR]

Nonuniform seismic excitation cannot be neglected in the seismic design of long-span tunnels in soft soil areas, as it might induce tunnel damage. This paper proposes a method that combines an integrated nonuniform seismic random excitation method with the finite element method to solve the problem of nonuniform seismic input for geotechnical tunnel seismic design in soft soil areas. The integrated nonuniform seismic random excitation method of producing multipoint random seismic waves is investigated considering the effects of passage, incoherence, and energy attenuation. Design codes are developed to achieve random seismic ground waves, baseline adjustment and filtering, and inversion of bedrock. The correctness of an integrated nonuniform seismic random excitation is verified by analysis of the differences (5%–10%) between the simulated and theoretical power spectrum functions. Based on this modelling, the dynamic responses of tunnels subjected to longitudinal and lateral seismic excitations are investigated. Nonuniform seismic excitation will cause greater tunnel deformation and internal forces than uniform seismic excitation due to the tunnel consuming more seismic energy under nonuniform seismic excitation. Longitudinal nonuniform seismic excitation induces compressive and tensile states in the tunnel, and the maximum tension is close to the tensile strength of the concrete. Lateral nonuniform seismic excitation can enlarge the bending moment and shear force, and bending moment and shear force distribution ranges are recommended for this case study. [ABSTRACT FROM AUTHOR]

This paper addresses the effect of particle gradation on the lateral response of pile in coral sand foundation through numerical method. Firstly, the parameters of Hypoplastic (HP) constitutive model were calibrated by a series of laboratory tests and show obvious difference in value between fine and coarse coral sand. Subsequently, a 50 g centrifuge test and 1g model pile test were carried out to verify the numerical model and calibrated parameters. Afterward, numerical analyses were systematically conducted to investigate the influence of particle gradation, buried depth, and relative density on the lateral response of pile. The lateral load–displacement response, deflection and bending moment of pile, and soil resistance were analyzed and discussed in detail. Numerical results show that the bearing capacity of pile and soil resistance in coarse sand are greater than those in fine coral sand when the relative density is 25 % or 50 %. However, when the relative density is 75 %, the bearing capacity of pile and soil resistance in fine sand present significantly greater values than those in coarse sand under higher lateral displacement level. Moreover, the difference in lateral response of pile between coarse and fine coral sand is more significant in looser sand or shorter pile. [ABSTRACT FROM AUTHOR]

A new p–y curve of the lateral static loading of large diameter piles in cohesive slopes is proposed in this paper, which considers both the size effect and slope inclination. A series of pile size and slope inclination varied three–dimensional finite difference analyses are used to study the behavior of large–diameter pile foundations under lateral loading on cohesive sloping ground. Based on the results of numerical calculations, the pile–soil failure mechanism is discussed for large–diameter piles. Combined with the failure mechanism, nonlinear analytical formulations are derived for the ultimate lateral load and initial stiffness of hyperbolic p–y curves at different depths, which considers both the size effect and slope inclination. The proposed p–y curve is compiled into a program for parametric analysis of pile displacement and bending moment. To verify the proposed p–y curve, it is compared with large–scale foundation lateral loading field test and centrifuge test data to obtain a remarkable result. [ABSTRACT FROM AUTHOR]

The available analytical methods are inadequate to quantify the displacement of embedded cantilever retaining (ECR) walls in working conditions owing to the intricacies present in the problem. The complexity of the problem further increases in the presence of a surface surcharge loading because, the loading intensity, width of the strip, and its distance from the wall significantly influence the wall behavior. This article presents an analytical method for the displacement-controlled analysis of rigid ECR walls in cohesionless soils, with a uniform strip surcharge placed on the backfill surface. The proposed method can be used to calculate the required embedment depth and the structural forces of an ECR wall while the wall displacement is prescribed. Alternatively, the wall displacement can be determined when the embedment depth, retaining height, and surcharge pressures are given. A displacement-dependent earth pressure mobilization approach is used to derive the soil pressures on the wall. Surcharge load-induced additional earth pressure on the wall is derived by adopting a suitable load distribution in the subsurface. The embedment depth of the wall is determined by assuming rigid rotation of the wall and satisfying the horizontal force and moment equilibrium. Analytical expressions are provided to calculate the bending moment distribution and the ground settlement profile behind the wall. The analytical results are compared with those of the numerical analyses performed in PLAXIS 2D. A parametric study was carried out to investigate the influence of the surcharge loading intensity, width of the strip, its distance from the wall, soil friction angle, wall roughness on the wall displacement and bending moment. [ABSTRACT FROM AUTHOR]

The influence of vertical spatial variability of sands on the excavation-induced lateral wall deflection and bending moment of excavations supported by cantilever retaining walls is investigated in this paper. Herein, the random finite element method (RFEM) is adopted to explicitly study the effect of one-dimensional spatial variability of internal friction angle of sands on the predicted wall and ground responses. The RFEM analysis consists of three components: (1) finite element method for analyzing lateral wall deflection and bending moment, (2) random field theory implemented with Monte Carlo simulation (MCS), and (3) statistical interpretation of MCS results through confidence intervals. This study reveals the importance of random field modeling in coping with the spatial variability of sands in the problem of supported excavations: (1) neglecting spatial variability of soil property will cause an overestimation of the variation in the predicted wall deflection and bending moment; (2) the estimated probability of failure based on a well-established serviceability limit state may be overestimated or underestimated depending on the chosen limiting lateral wall deflection. This study further investigates the effect of the number of MCS on the confidence intervals of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment. The results also demonstrate that the confidence interval analysis of the predicted statistics of the maximum lateral wall deflection and the maximum bending moment provides a rational tool for interpreting the statistical data from RFEM. [ABSTRACT FROM AUTHOR]

Under seismic excitation, a pile undergoes stresses stemming from both the vibration of the surrounding soil (kinematic interaction) and that of the superstructure (inertial interaction). The relative contributions of kinematic and inertial interaction on the magnitude of seismic forces induced in pile foundations are investigated by means of nonlinear two-dimensional (2D) finite element (FE) analyses. The interaction between the pile and the surrounding soil in three-dimensional (3D) type was idealized in the 2D analysis using soil–pile interaction springs with hysteretic nonlinear load displacement relationships. Parametric analyses are carried out, focusing on normalized seismic forces in the piles as affected by typical characteristics of structures and piles as well as ground nonlinearity. The results of the study provide a new interpretation of the interplay between pile kinematic and inertial seismic forces. The numerical results showed that for relatively short/stiff piles or where structure’s natural frequency is lower than that of the ground, the kinematic interaction can be the prime contributor to the seismic forces in the pile provided that the excitation frequency is not close to the natural frequency of the coupled soil–pile–structure system, f SSI . In a frequency band approaching f SSI , the inertial interaction generally prevails imposing large bending moments at or near the pile head. The results showed also that maximum kinematic seismic force does not always occur at the fundamental frequency of the deposit. For certain relative soil–pile stiffness and excitation amplitudes, the largest peak of the kinematic seismic forces in piles can be occurring at the second mode. [ABSTRACT FROM AUTHOR]

The behaviour of a test embankment constructed on a soft clayey deposit in Saga, Japan, was simulated by both three-dimensional (3D) and two-dimensional (2D) finite element analyses (FEA). Floating soil–cement columns had been installed in the clay prior to construction of the embankment. Comparing the results of 3D and 2D FEA indicates that 2D analysis predicts incorrect results in terms of the lateral displacement and bending moment in the columns under the toe of the embankment. In the 2D analysis, the rows of columns were modelled by continuous walls, which partially block the interaction between the soil layers and the columns and influence the simulated lateral displacement and bending moment in the column. It has been postulated that compaction of fill material during the construction process has a significant influence on both the magnitude and pattern of the lateral displacement of the column under the toe of the embankment. Pragmatically, this influence can be indirectly simulated by reducing the stiffness and increasing Poisson’s ratio of the embankment fill material. Finally, both the measured and FEA results indicate that the columns not only reduced the total settlement but also accelerated the settlement rate of the deposit under the embankment loading, due to the much higher stiffness of the column material. [ABSTRACT FROM AUTHOR]

Abstract: In designing piled raft foundations, controlling the total and differential settlements as well as the induced bending moments of the raft is crucial. The majority of piled raft foundations have been designed by placing piles uniformly. In such a design method, the settlements of the piled rafts are likely to be large, which leads to an increase of the pile length and/or number of piles required to reduce the settlements. However, this increase does not satisfy the requirement for economical design. On the basis of a parametric study, this paper contributes a framework for considering an economical design methodology in which piles are placed more densely beneath the column positions when the piled raft is subjected to column loads. The analysis uses PLAXIS 3D software, and the validity of the parametric study is examined through the results of centrifuge model tests conducted by the authors. The study shows that the concentrated pile arrangement method can help to considerably reduce the total and differential settlements as well as the induced bending moments of the raft. Moreover, the effects of parameters, such as pile length, pile number, raft thickness and load types, on the piled raft behavior are investigated. This study can help practicing engineers choose pile and raft parameters in combination with the concentrated pile arrangement method to produce an economical design. [Copyright &y& Elsevier]

Many monopile-supported offshore wind turbines (OWTs) have been installed in seismic regions. To determine the seismic response of monopile-supported OWTs accurately, it is crucial to simulate dynamic soil-pile interactions properly. Meanwhile, the additional soil nonlinearity caused by wind–wave loadings and pile scour induced by wave–current actions make seismic analysis more challenging. However, current guidelines for the seismic design of OWTs often fail to adequately consider the above problems. This study creatively presents an integrated analysis of the dynamic responses of scoured monopile-supported OWTs under combined seismic, wind and wave excitations. A novel dynamic p–y relationship being capable of reasonably reflecting soil degradation is adopted to model the soil–pile interactions. The effects of combined stochastic wind–wave and hydrodynamic loads, and different scour conditions are comprehensively incorporated in the OWT model to conduct the systematic seismic analyses. The results indicate that scour can induce excessive displacement and bending moments in an OWT structure under combined loads, threatening its safe operation. With increasing scour depth, the load combination effect becomes less pronounced, and the responses are mainly induced by wind–wave loads. These results can shed light on the seismic response of monopile-supported OWTs located in complex paralic environments. [ABSTRACT FROM AUTHOR]

Abstract: Elastic–plastic, closed-form solutions were developed recently by the author, to capture the nonlinear response of laterally loaded rigid piles. Presented in compact form, the solutions are convenient to use, and sufficiently accurate despite using only two input parameters of the net limiting force per unit length pu along the pile, and a subgrade modulus k. Nevertheless, piles may be subjected to limited cap-restraints or loading below ground surface, which alter the response remarkably. This paper provides explicit expressions for estimating loading capacity of anchored piles and develops new solutions for lateral piles with cap-rotation by stipulating a constant pu or a linear increasing pu (Gibson pu ) with depth. Lateral loading capacity Ho (at the tip-yield state and yield at rotation point state) and maximum bending moment Mm (at the tip-yield state) are presented against loading locations, and in form of the lateral capacity Ho − Mo (applied moment) locus. The capacity is consistent with available solutions for anchored piles, and caissons with either pu profile, allowing a united approach from lateral piles to anchored piles. The new solutions are also presented in charts to highlight the impact of rotational stiffness of pile-cap on nonlinear response, offering a united approach for free-head piles through fixed-head piles. Several advantages of the solutions are identified against the prevalent p–y curve based approach. To estimate the key parameter pu , values of the resistance factor Np (=ratio of pile–soil limiting resistance over the undrained shear strength su ) are deduced using the current expressions against available normalised pile capacity involving the impact of gapping (between pile and soil), pile movement mode, pile slenderness ratio, inclined loading angle (anchored piles) and batter angles (lateral piles). The Np is characterised by: (i) An increase from 5.6–8.6 to 10.14–11.6, as gapping is eliminated around lateral piles and caissons, and from 1.0–6.1 to 2.8–9.8, as translation is converted into rotation mode of footings. (ii) Similar variations with slenderness ratio between anchors and caissons (without gapping), and among anchors, caissons and pipelines (with gapping). And (iii) A reduction with loading angles (anchors) resembling that with batter angles (piles). [Copyright &y& Elsevier]

Abstract: In conventional design, continuous buried steel pipes are designed based on their transverse behavior where low stiffness zones of soil, uncertainties in soil and structure properties are not considered. Winkler’s analytical model and the FOSM method are used to estimate uncertainties in terms of the coefficient of variation in the differential settlement (CVΔ ) and the bending moment (CVM ) as the function of the uncertainties in the subgrade reaction modulus (ks ) and the low stiffness zone length beneath the pipe. Results show that the values of CVΔ and CVM are very different depending on the uncertainties of ks and the length of the low stiffness zone. [Copyright &y& Elsevier]

Abstract: The construction of sheet pile walls may involve either excavation of soils in front or backfilling of soils behind the wall. These construction procedures generate different loading conditions in the soil and therefore different wall behavior should also be expected. The conventional methods, which are based on limit equilibrium approach, commonly used in the design of anchored sheet pile walls do not consider the method of construction. However, continuum mechanics numerical methods, such as finite element method, make it possible to incorporate the construction method during the analyses and design of sheet pile walls. The effect of wall construction type for varying soil conditions and wall heights were investigated using finite element modeling and analysis. The influence of construction method on soil behavior, wall deformations, wall bending moments, and anchor forces were investigated. The study results indicate that walls constructed by backfill method yield significantly higher bending moments and wall deformations. This paper presents the results of the numerical parametric study performed and comparative analyses of the anchored sheet pile walls constructed by different construction methods. [Copyright &y& Elsevier]

Abstract: Reinforced soil walls commonly include facing elements which affect the mechanical behavior of the system. However, the design procedures involved in the existing codes and manuals (e.g. FHWA, BS8006, AASHTO, etc.) do not consider the structural contribution of the facing to the wall stability. Recently, a new computer based method for the analysis of reinforced soil walls which takes into account the interaction between the facing and the soil reinforcement layers was presented [Klar A and Sas T. Rational approach for the analysis of segmental reinforced soil walls based on kinematic constraints. Geotextiles and Geomembranes 2009;27:332-340]. This method demands full compatibility between the reinforcement layers and the deforming wall, and is solved as an optimization problem on this constraint. This kinematic compatibility (KC) method entails several assumptions regarding the interaction between the three components of the system (soil, wall, and reinforcement). This paper compares the KC method to a more rigorous continuum analysis. Results show that the KC method is capable of replicating the behavior of the more rigorous system, with a good agreement on both the value of maximum tensile forces in the reinforcement and shear and bending moment distributions along the wall. The KC method has a certain advantage over continuum methods, such as finite element or finite difference, since it requires limited input data that can easily be obtained from field tests. [Copyright &y& Elsevier]

An improved method is proposed for the design of cantilever sheet pile walls embedded in cohesionless soils and having an infinite uniform surcharge load under both static as well as seismic conditions in the framework of limit equilibrium. The proposed method considers the rigid rotation of cantilever sheet pile walls about a pivot point located near the toe of the wall following the displacement pattern. It considers the partial mobilization of earth pressures which is a function of lateral strain and depends on the magnitude and type of wall movements. Expressions are proposed to calculate the earth pressures on both sides of the wall in addition to shear force and bending moment at various depths. The penetration depth is obtained by considering horizontal force and moment equilibrium conditions simultaneously. The proposed method is compared with numerical, theoretical and experimental results under static as well as seismic conditions. It is found that the results proposed by this method and available literature are fairly good and reasonable. A parametric study is carried out to analyze the influence of friction angle of soil, magnitude and distance of surcharge under both static as well as seismic conditions. [ABSTRACT FROM AUTHOR]

Abstract: A numerical method that takes into account the coupling between the rigidities of the piles, the cap, and the column has been developed for analyzing the response of pile group supported columns. Special attention is given to consideration of pile cap flexibility. A load transfer approach using t–z/q–z and p–y curves is used for the analysis of single piles. The finite element technique is used to combine the pile stiffness with the stiffness of the cap and column. The numerical method developed has been verified by comparing the results with other numerical methods for pile groups. Through comparative studies, it has been found that the maximum load on the individual piles in a group is highly influenced by pile cap flexibility. The prediction of the lateral loads and bending moments in the pile cap is much more conservative in the present analysis than in FBPier 3.0 and shows a definitely larger lateral load and bending moment for various cap thicknesses. [Copyright &y& Elsevier]

This paper presents a theoretical method for the horizontal mechanical responses of single pile due to tunnelling in multi-layered soils. Based on the homogenization theory and the integral L&P formula, ground horizontal displacements due to tunnelling in layered soils can be solved analytically. The pile-soil interaction model is established in which the pile is assumed to be an Euler-Bernoulli beam placed on the Pasternak foundation. According to the two-stage thought, the horizontal displacements and bending moments of the pile can be evaluated quantitatively if the calculated horizontal displacements are input into the interaction model. The proposed method is verified by comparing with the numerical method, field measurement and centrifugal test. Parametric analyses are also performed to investigate the influence of the parameters of the pile and excavation, especially the soil stratification on the mechanical responses of the pile. Results found that the GAP parameter, the distance of tunnel axis from pile axis, the length, the diameter and the elastic modulus of the pile all have an important influence on the horizontal displacements and bending moments of the pile. Importantly, the soil stratification has a non-negligible influence on the mechanical responses of the pile. The stiff interlayer sandwiched between the upper and lower soil layer can significantly limit the horizontal displacements of the pile but increase the bending moments. [ABSTRACT FROM AUTHOR]

• Eccentric and/or inclined loads induce nonlinear roto-translational displacements of pile groups. • Simplified modelling (beams, elastic half-space, localised yielding) compared with advanced analyses. • Vertical eccentric loads mobilise the lateral soil resistance at large cap displacements. • Charts for the reduction in vertical capacity, at prescribed cap displacements, due to load eccentricity and inclination. This paper presents a numerical study of 3 × 3 pile groups embedded in clay under vertical and inclined eccentric loads. Simplified modelling, based on elastic beams embedded in a soil continuum, is used to explore the soil-pile-cap response. This simple model allows rigorous treatment of the 3D foundation geometry and local soil plasticity, demonstrated through validation with 3D finite element analysis. The numerical results reveal that complex roto-translational displacements of the pile group are induced by eccentric or inclined loads, with highly nonlinear relationships when soil plasticity is considered. Interestingly, vertical eccentric loads mobilise the lateral soil resistance at large cap displacements. Thus, while existing t-z type models are shown to be adequate for serviceability predictions, they could provide overly-conservative estimates of the ultimate load capacity. Also, foundation internal forces can exceed allowable bending moments of reinforced concrete piles under multi-directional loads. For performance based design of pile groups under inclined eccentric actions, engineers should estimate the impact of soil yielding on both displacements and rotations of the cap, to satisfy limit state requirements. Dimensionless charts are presented, which describe the reduction in vertical capacity, for a prescribed cap displacement, as a function of load eccentricity and inclination. [ABSTRACT FROM AUTHOR]

In this paper, a thorough numerical study is conducted to rigorously evaluate the lateral earth pressures exerted on the retaining walls backfilled with geosynthetic-reinforced soil strata. With this aim, the lower bound theorem of limit analysis is exploited in conjunction with the finite element discretization method. The computational programming adopting second-order cone optimization is employed to model the Mohr-Coulomb yield criterion in its respective nonlinear form. The reinforcement layers are assumed to bear solely axial tension; but not bending moment, which is the common characteristic of all geosynthetic materials. Results show that the horizontal stress field behind retaining structures is heavily disturbed by placing geosynthetic layers, especially in close proximity to the retaining structure. Accordingly, the failure zone shrinks in size and the lateral earth pressure decreases by either adding more reinforcement layers or increasing their relative lengths. Through a comprehensive parametric survey, the influence of several parameters, including internal friction angle, soil-wall and soil-reinforcement interface friction angles, length and number of reinforcements, soil inherent anisotropy and surface loading on the lateral earth pressure is meticulously examined. The employed formulations are rigorously compared with results published in the literature. A design table is also provided so as to effectively estimate the active earth pressure coefficient of geosynthetic-reinforced walls accounting for all contributing parameters. [ABSTRACT FROM AUTHOR]

It is very important to analyze the lateral cyclic response of monopiles for the design of offshore wind turbines (OWTs). A three-dimensional finite element method for lateral cyclic responses of large-diameter monopiles is developed based on a simplified constitutive model of clays that has been successfully encoded into the ABAQUS software package. The applicability of this method is validated by simulating the existing centrifugal model test. The method can predict the nonlinear hysteresis responses of monopiles in clays during cyclic loading, and the evolution of bending moment and lateral deflection profile of monopile with loading cycles. Various lateral cyclic loads with different loading patterns including one-way and two-way loading, symmetric and asymmetric loading, variable-amplitude and constant-amplitude loading are applied to monopiles. The impact of different cyclic loading patterns on lateral responses of large-diameter monopiles is systematically investigated. The research results can provide some reference for the engineering design of large-diameter monopiles under lateral cyclic loads. [ABSTRACT FROM AUTHOR]

A concrete cut-off wall has been recently used in a landslide dam as an anti-seepage measure. Due to it is under a complex loading condition, the wall may undergo inelastic straining and have a potential of cracking. Several centrifuge model tests and numerical simulation are conducted to investigate the damage behavior of the cut-off wall. The numerical method of concurrently modelling small cracks in the cut-off wall and the overall landslide dam based on the finite element method (FEM)-Peridynamics (PD) multiscale coupling method is confirmed to be effective by the centrifuge model tests. The cut-off wall buried in a landslide dam bears a bending effect under lateral loadings in the absence of overlying fill. The lower part of the wall may have a potential to form cracks induced by large bending moments. The wall is in a tension-shear failure mode with an inclined crack. A parametric study demonstrates that properties of the wall and the soil have a significant effect on the damage behavior of the wall. Also, creep deformation of the dam body does not elongate the crack significantly, but it expands the width of the crack. The crack tends to stabilize over a period of time. [ABSTRACT FROM AUTHOR]