Pile Embedment Research Articles

Three-dimensional numerical analysis of the effect of foundation stiffness on soil-structure interaction

Stiffness-related geometric characteristics are closely linked to the performance of structural systems. The influence of foundation stiffness on the soil-structure interaction (SSI) mechanism was investigated by numerical modeling of different building foundations. Numerical tools (PLAXIS 3D and TQS/CAD) were used for decoupling analyses of the interaction between the structural components. Results obtained from instruments installed in a building case study were used to refine the numerical calculations. Linear elastic constitutive models and beam elements were useful in reducing computational processes and ensuring study feasibility. The simulation results provided a satisfactory representation of field observations. Interaction between piles and the environment governs the relationship between foundation stiffness and uniform settlement. Rigid pile groups are achieved with greater pile length, diameter and spacing. This study highlights the different effects of pile geometric parameters on loading and unloading rates in pillars, demonstrating that the SSI mechanism is more sensitive to less rigid foundations, particularly those with greater pile embedment. It was concluded that numerical simulations to predict settlement as realistically as possible require understanding and selecting the most appropriate model and type of calculation.

Numerical simulation study on the embedding depth of anti slip piles in fully weathered granite landslides

Abstract Taking the reinforcement project of the fully weathered granite landslide in Fanling as the research object, this study establishes a numerical slope model with anti-slide pile reinforcement, the most common means in slope reinforcement engineering, while considering the pile-soil interaction. Using the strength reduction method, the effects of different anti-slide pile embedment depth on the stability of the reinforced slope are discussed. The research results indicate the following findings. (1) The embedment depth is negatively correlated with the slope displacement. (2) When the embedment depth is more excellent than 7m, the slope Factor of safety is 2.032>2.0, which meets engineering safety requirements. (3) According to the changes in displacement and the factor of safety, the stress analyses of the pile body and the economic factors, the optimal embedment depth for the Fanling landslide are determined as 8 m. The results afford certain application and promotion values by providing theoretical references and technical guidance for similar anti-slide pile reinforced slope projects.

Numerical Analysis of Block Type Quay Wall with Piles for Restraining Horizontal Deformation

A two-dimensional numerical analysis was performed on the depth of pile embedment, the magnitude of the residual water level, and the condition of the presence or absence of cap concrete to understand the behavior of the block-type quay wall with piles. The results showed the control effect of the lateral displacement of the quay wall depending on the embedment of the pile. When the piles were not embedded, the lateral displacement of the quay wall increased proportionally as the residual water level difference increased. In contrast, when the piles were embedded into the ground, the control of the lateral displacement of the quay wall was greatly exerted even if the residual water level difference increased. There was little difference in the lateral displacement of the block-type quay wall regardless of the presence or absence of cap concrete. Under the condition where the piles were embedded down to the rubble mound layer, the piles exhibited the rotational behavior seen in the short piles. As the embedment depth of the piles increased, the piles showed the same bending behavior as the intermediate piles. Thus, the piles significantly contribute to the control of lateral displacement in the block-type quay wall with piles.

Effect of Permanent Load in Gresik Alluvium on Friction Pile Embedment Depth

Hydrostatic load, approximately 250-35 kPa (i.e., water of 2.5m-3.5m high), has been applied in the project area for about 25 years; hereafter, it will be referred as permanent load. Recently, this permanent load including its perimeter embankment, is demolished for which a new facility will be built. The upper 2-4m soil layer in this area consists of fill soil (mainly cohesionless material) overlying thick Gresik alluvium layer. A bearing layer was not found (down to an investigation depth of 50m). The initial design of pile embedment depth refers to the legacy soil report, pile embedment information from the surrounding area (not being subjected by permanent load), and preliminary soil investigation data (from the surrounding area); in this case, the projected embedment depth is 20-23m with the friction pile design concept. Due to the proximity of project location with existing facilities, the jacking-driven pile method, with HSPD (Hydraulic Static Pile Driver) machine, is selected for installing the precast spun pile. The pile jacking works indicate that piles can only be driven down to a depth of about 12m (far less than the projected depth). This paper provides an analysis on the changes of soil properties due to permanent load, which in turn increasing the pile shaft capacity and effectively reducing the pile embedment depth. The analysis is supported by data from pile jacking record, PDA test, and instrumented test pile. Discussion regarding the conservatism in pile design is also presented.

Elastic–Plastic Analysis of Rigid Passive Piles in Two-Layered Soils

The paper analyses the behavior of a rigid passive pile embedded in a soil profile consisting of a stable layer underlying an unstable layer subjected to a uniform soil displacement. Pile-soil interaction is considered by modeling the soil by a series of elastic–plastic springs along the pile shaft. The modulus of horizontal subgrade reaction is assumed to linearly increase with depth in the unstable layer and constant in the stable one. The ultimate soil resistance is assumed increasing with depth in both layers. The results of analysis are presented in dimensionless form in terms of shear force developed at the slip surface as a function of the pile embedment into the stable layer and the distribution of soil characteristics over depth. The method allows capturing pile response not only at the soil ultimate state but also at the intermediate states. Specifically, the governing equations for the elastic, elastic–plastic and plastic cases are discussed and, whenever possible, a set of closed-form expressions is provided to estimate the maximum bending moment along the shaft and the pile head deflection, so that for an assigned value of the required stabilizing force both ultimate and serviceability limit state of the pile can be checked. A numerical example is given to illustrate the application of the proposed procedure.

ANALYSIS AND PRELIMINARY DESIGN OF A TANGENT BORED PILE WALL AS AN ALTERNATIVE TO CONVENTIONAL BREAKWATERS

Based on existing construction practices, and the difficulty of sourcing rock armor materials in the Philippines, an alternative to conventional rubble mound breakwaters was considered for a beach resort development in Cebu, Philippines. A tangent bored pile wall, consisting of circular piles placed diametrically along a specified alignment, was analyzed and designed as a breakwater. It relies on pile embedment depth and soil friction for stability, unlike conventional breakwaters which rely on the weight of the armor rocks and the interlocking of individual armor units.

Analysis Methods for the Design of Pile–to–Pile Cap Connections Concerning Plain Pile Embedment

Analysis Methods for the Design of Pile–to–Pile Cap Connections Concerning Plain Pile Embedment

Effective foundation damping prediction of monopile-supported offshore wind turbines based on integrated fitting equation and PSO–SVM algorithm

Foundation damping affects the fatigue life of offshore wind turbines. However, the effective damping ratio determined using a finite element analysis is not always consistent with the input. A series of simplified finite element models were established using realistic structural properties for a monopile-supported wind turbine to analyze the influence of wall thickness, pile embedment length, structure density, and input damping ratio on the calculated effective damping ratio. An empirical fitting equation was proposed using a power function based on the comprehensive laws between various factors and the effective value. An integrated prediction approach combining this equation with a hybrid support vector machine and particle swarm optimization algorithm was subsequently described and its results compared with those of other intelligent algorithms. The results showed that the effective damping ratio was much smaller than the input value, with the former reaching a maximum of only 15% of the latter. The integrated prediction approach was shown to strike an equilibrium between computing efficiency and forecast accuracy. Considering the soil–structure interaction and elastoplastic behavior of soil only increased the effective damping ratio to 35% of the input value, and also obfuscated the roles of the various factors in the effective damping.

Application of artificial neural networks for predicting the bearing capacity of the tip of a pile embedded in a rock mass

Addressing the problem of the bearing capacity of the tip of a pile in rock needs to consider a full-nonlinear behavior of the rock, as the Hoek and Brown failure criterion, and including the various geometric parameters defining the system geometry. It usually needs the use of complex numerical models. They require a high level of training and expertise and are commonly out of the reach of engineers on the day-to-day calculation procedures. Technical codes usually recommend simpler formulae based on one or two rock parameters, their accuracy relying on particular and local empirical testing. This research develops an artificial neural network (ANN) that solves the previous difficulties. The ANN is based on a group of 1440 calculations using the novel numerical procedure Discontinuity Layout Optimization (DLO). This numerical method can efficiently reproduce the non-linear behavior of the rock (including rock type, uniaxial compressive strength, and geological strength index) for every configuration of the model (foundation width, pile embedment, and height of the overlying soil). Once the ANN is trained and optimized, it can easily predict any result within its range of applicability. Furthermore, it can be reduced to a simple set of recursive equations to be implemented in a spreadsheet. The proposed ANN has only one hidden layer besides the input and output layers, with (6)-(8)-(1) neurons, respectively. It gives highly accurate results with minimum cost and can be a useful tool for engineers and scientists in the foundation field.

A poroelastic model for near-field underwater noise caused by offshore monopile driving

Impact monopile driving in the offshore wind industry generates extremely high sound pressure levels in the water. Previous studies have simplified the seabed as either an acoustic medium or an elastic medium, which may not be appropriate for certain offshore environments. In this paper, the seabed is modelled as a poroelastic medium using Biot's theory, which can consider pile driving noise in soils with partially drained conditions. For saturated clays and silts, the sound pressure level in the poroelastic model can be approximated by the elastic model using the same soil P-wave and S-wave speeds. For saturated sands, the noise level in the poroelastic model is generally lower than that in the elastic seabed model. The new noise attenuation mechanism is due to the relative displacement between the pore fluid and the soil skeleton. The effects of several key parameters in the poroelastic model, such as the soil permeability, soil shear modulus and degree of soil saturation, are analysed in detail. Generally, the noise level is higher in stiffer, fully saturated soils with lower permeability. The noise level in unsaturated soil is always lower due to the compression of small air bubbles in the soil. The contributions of the pseudo-Scholte wave and Biot's slow compressional wave are also discussed. In addition, a parametric study of pile radius and pile embedment depth is highlighted. The proposed model is a useful addition to the existing simplified models.

Design optimization of offshore wind jacket piles by assessing support structure orientation relative to metocean conditions

Abstract. The orientation of a three-legged offshore wind jacket structure in 60 m water depth, supporting the IEA 15 MW reference turbine, has been assessed for optimizing the jacket pile design. A reference site off the coast of Massachusetts was considered, including site-specific metocean conditions and realistically plausible geotechnical conditions. Soil–structure interaction was modeled using three-dimensional finite-element (FE) ground–structure simulations to obtain equivalent mudline springs, which were subsequently used in nonlinear elastic simulations, considering aerodynamic and hydrodynamic loading of extreme sea states in the time domain. Jacket pile loads were found to be sensitive to the maximum 50-year wave direction, as opposed to the wind direction, indicating that the jacket orientation should be considered relative to the dominant wave direction. The results further demonstrated that the jacket orientation has a substantial impact on the overall jacket pile mass and maximum pile embedment depth and therefore represents an important opportunity for project cost and risk reductions. Finally, this research highlights the importance of detailed knowledge of the full global model behavior (both turbine and foundation) for capturing this optimization potential, particularly due to the influence of wind–wave misalignment on pile loads. Close collaboration between the turbine supplier and foundation designer, at the appropriate design stages, is essential.

Centrifuge Model Tests Investigating Initiation and Propagation of Pile Tip Damage during Driving

A number of incidents of pile tip damage and extrusion buckling have been reported within the offshore industry, generally arising during driving of relatively thin-walled tubular pile foundations through hard layers or potentially heterogeneous sediments. The issue has become of particular concern with modern trends toward larger diameter piles, with higher ratios of diameter to wall thickness, for monopile or jacket foundations of offshore wind turbines. The paucity of good-quality data available in the public domain about this kind of failure has impaired the development of simple design guidelines for industry to address the issue. The paper presents results from a series of centrifuge model tests where pile tip damage and extrusion buckling were observed during driving of either (1) undamaged cylindrical piles into a sand bed containing a layer of different sizes of boulders, or (2) predented piles into medium dense homogeneous sand. Following a previously reported pilot study, a new and higher energy model pile-driving hammer was designed to permit driving through the hard layers and allow pile embedment by up to five diameters. Two test beds were prepared, one of which contained boulder layers of different sizes either near the surface or at a depth of about one pile diameter, into which piles of two different diameter to wall thickness ratios were driven. The test series led to observations of pile tip damage that ranged from abrupt tip crumpling to gradual extrusion buckling. For 2 of the 22 piles installed, dent growth during installation was detected by optical fiber sensors attached to the piles. For the uninstrumented piles, damage was deduced from the trends in blow counts during installation, with later confirmation from detailed visual inspections and laser scanning, and also from careful layer by layer excavation of each sample. The high-quality database generated from the model tests forms a valuable resource for further study and validation of advanced numerical models to simulate pile tip damage and for calibration of simple guidelines for practical design.

Two-dimensional Analysis of the Group Interaction Effects Between End-bearing Piles Embedded in a Rock Mass

This research is a two-dimensional analysis of the interaction effect in a group of piles socketed in a rock mass when studying the end-bearing capacity of the group. This problem was extensively studied for deep foundations in soils, but very little is published about foundations in rock. The study was conducted in 2D to establish the basis and criteria to analyze the problem, as well as understand the main factors and failure mechanisms involved when several piles work together in a foundation. The factors included in the analysis are, among others: the parameters of the rock mass, the pile embedment, and the pile separation. The research highlights shaft resistance as one of the key factors in the interaction. It proves that neglecting shaft resistance changes the interaction influence and the failure mechanism which may not be on the safe side. The research includes an analysis of the failure modes of different pile configurations using the discontinuity layout optimization (DLO) method, by taking advantage of the method’s ability to show the wedge configuration at the failure. The minimum and maximum efficiencies are characterized in terms of the pile separation values, thereby proposing a procedure to obtain the absolute minimum efficiency of the group. A second procedure is also presented for the approximate prediction of the bearing capacity of the pile tip, for a group with a particular number of piles and properties, by considering the contribution of the corner piles and the intermediate piles.

Failure mechanism of single pile-friction footing hybrid foundation under combined V–H–M loadings by PIV experiments and FE method

The traditional monopile foundation is confronted with challenges in the context of the new generation of offshore wind turbines with greater power capacities. On this basis, the single pile-friction footing hybrid foundation is investigated, whose bearing capacity is largely improved by combining a circular friction footing at the mudline. This paper discusses the failure mechanisms and bearing capacities of this hybrid foundation in sand under combined vertical-horizontal-moment (V–H-M) loadings by laboratory experiments and the finite element method. By adopting Particle Image Velocimetry (PIV) technology in model tests, failure mechanisms of a single pile and the hybrid system are compared. The results show that the cavitation and compaction phenomenon can be captured in the depth range of 0–0.7 pile embedment depth) for the hybrid foundation. Also, due to the settlement of the footing, a deformation area with a concave area and a small peak value can be found under the footing, which is quite different from that of the pile under V–H-M combined loadings. Intensive parametric studies were performed through FE method, and the results indicate that increasing the footing diameter has a more pronounced effect on the bearing capacity compared to that of increasing the length-diameter ratio of the pile.

Influence of Vertical Load on Lateral-Loaded Monopiles by Numerical Simulation

Monopiles are the most common foundation form of offshore wind turbines, which bear the vertical load, lateral load and bending moment. It remains uncertain whether the applied vertical load increases the lateral deflection of the pile. This paper investigated the influence of vertical load on the behaviour of monopiles installed in the sand under combined load using three-dimensional numerical methods. The commercial software PLAXIS was used for simulations in this paper. Monopiles were modelled as a structure incorporating linear elastic material behaviour and soil was modelled using the Hardening-Soil (HS) constitutive model. The monopiles under vertical load, lateral load and combined vertical and lateral loads were respectively studied taking into account the sequence of load application and pile slenderness ratio (L/D; L and D are the length and diameter of the pile). Results suggest that the sequence of load application plays a major role in how vertical load affects the deflection behaviour of the pile. Specifically, when L/D ratios obtained by lengthening the pile while keeping its diameter constant are 3, 5 and 8, the relationships between lateral load and the deflection behaviour of the pile under the effect of vertical load demonstrate a similar trend. Furthermore, the cause of increased lateral capacity of the pile under the action of applied vertical load in the common practical application case and in the VPL case was analyzed by studying the variation law of soil stress along the pile embedment. Results confirm that the confining effect of vertical load increases means effective stress of the soil around the pile, thus increasing soil stiffness and pile capacity.

Lateral Bearing Capacity of a Hybrid Monopile: Combined Effects of Wing Configuration and Local Scour

Pile foundations for offshore wind turbines are subjected to large lateral loads. By mounting wings on the perimeter of regular monopiles, winged monopiles have shown better performance in resisting deformation under horizontal loading. However, the hazardous effect of local scour on the lateral bearing capacity of winged monopiles installed in the sandy seabed has not been systematically evaluated. In this study, a modified Mohr–Coulomb model considering the pre-peak hardening and post-peak softening behavior of dense sand is adopted to simulate laterally loaded winged monopiles in the locally scoured sandy seabed, using three-dimensional finite element analyses. The effect of local scour depth on the lateral capacity of winged monopiles is examined and explained by soil failure mechanisms. The enhancement of lateral capacity with wings attached to the monopile is demonstrated to be more effective than extending pile embedment length. The effects of the relative density of sand and the wing load orientation are also discussed. Finally, the wing efficiency is evaluated to determine the optimal configuration of winged monopiles.

Numerical Study on Pile Group Effect and Carrying Capacity of Four-Barreled Suction Pile Foundation under V-H-M Combined Loading Conditions

Multi-barreled composite foundations are generally used in offshore oil platform structure. However, there is still a lack of theoretical analyses and experimental research. This paper presents the results of a three-dimensional finite element analysis of a four-barreled suction pile foundation in heterogeneous clay foundation. The pile group effect and carrying capacity are numerically simulated. The effects of different pile embedment depths, pile spacings and non-uniformity coefficients of clay on the pile group effect are studied. Considering the changes in the foundation carrying capacity under vertical, horizontal and bending moment coupling loads, the foundation carrying capacity envelopes under horizontal and moment (H-M) and vertical, horizontal and moment (V-H-M) loading modes are drawn. The results show that pile spacing and embedment depth have great influence on the pile group effect. The bearing capacity envelope of foundations under V-H-M loading mode is greatly affected by vertical load V. This can provide a reference for the selection of pile spacing and embedded depth in practical engineering design. Furthermore, the stability of foundations can be evaluated according to the relative relationship between design load and failure envelope.

Application of the modified Hoek-Brown criterion in the analysis of the ultimate bearing capacity at the tip of a pile in inclined rocks

To calculate the ultimate bearing capacity at the tip of a pile in inclined and highly fractured rocks (GSI≤ 25), the exponent “a” is incorporated in the resolution approach to generalize the formulation of the original Hoek-Brown failure criterion. This exponent, with values close to 0.5 for good geomechanical qualities of the rock mass, has significantly higher values for GSI less than 25. An analytical formulation was developed that allows a suitable understanding of the geomechanical behavior. Thus, different exponent “a” and tensile strength coefficient will lead to the development of different failure modes of piles. Presented here are the mathematical equations obtained to resolve the bearing capacity and the charts used to determine the bearing capacity factor based on the slope angle of the rock and the exponent “a”. In addition, it is demonstrated that to get the same ultimate bearing capacity at the pile tip, the pile embedment ratio increased with an increasing rate as the exponent a of modified Hoek-Brown increased. Through this research it is shown that the modified Hoek-Brown criterion can be applied to highly fractured media of rock mass efficiently to estimate the bearing capacity of piles in inclined slope.

A multi-material ALE model for investigating impact dynamics of pile-soil systems

The dynamic pile-soil interaction is one of the most important and challenging problem in geomechanics, especially when geometrical, material-related, and dynamic contact-related nonlinearities exist. Geometrical nonlinearity is a fundamental obstacle to the popular Lagrangian finite element methods (FEM) that have been utilized in other areas of geomechanics research. This paper introduces a Multi-Material Arbitrary Lagrangian-Eulerian (MM-ALE) model for predicting the pile-soil interaction and forces during lateral dynamic impact events. The study used the MM-ALE method in conjunction with an elasto-viscoplastic soil material model that included strain softening and an elasto-plastic steel material model that incorporated strain rate effects to examine pile response during lateral vehicle impacts. The model was validated using large-scale, dynamic impact test data for piles embedded in soil, thus confirming its capability to simulate the complex dynamic impact pile-soil interaction. The effects of impact velocity, embedment depth, and soil strength on impact forces, energy dissipation, and impulse response of a pile-soil system were subsequently investigated. It was determined that average impact force, Favg, and impact velocity, are proportional to one another as Favg∝v2 regardless of pile embedment depth. This relationship provides evidence for the existence of inertial or hydrodynamic drag forces in the pile-soil system during lateral impacts similar to a solid object passing through a fluid.

Recent Advances in Laterally-Loaded Piles within Mechanically-Stabilized Earth Walls

Pile foundations have been increasingly installed within mechanically-stabilized earth walls (MSE) on rocks or compressible soils to support structural loads. Integral abutment bridges, sound walls, and traffic signs are common examples of the structures supported by pile foundations installed within or behind MSE walls. These structures are often subjected to lateral loads resulting from earthquakes, traffic loads, wind loads, and/or thermal expansion and contraction of bridge girders. Typical approaches available to design MSE walls are limited to MSE walls without pile foundations present within reinforced fill. To minimize the interaction between piles and the MSE wall, designers often suggest to place the piles at a distance of six to eight times the pile diameter and/or isolate the piles from the MSE wall by using corrugated pipes. These suggested designs lead to increasing the cost of projects by increasing the length of bridge spans or the diameter of piles and requiring pile embedment. Recently, several studies have been conducted to understand the interaction between piles and MSE walls when the piles are constructed within and close to wall facing. This paper provides a literature review on full-scale tests, reduced-scale tests, and numerical studies of piles constructed within or behind MSE walls. The review will focus on the effects of three key influence factors on lateral capacities of laterally-loaded piles and facing deflections of MSE walls including the plie location behind the wall facing, the ratio of the reinforcement length to the wall height, and the stiffness of the reinforcement layer. This paper will also discuss the available approaches to estimate the forces in the reinforcement layers and the lateral earth pressures behind the MSE wall facing due to the laterally-loaded piles.