Vertical Piles Research Articles

Application of a Eulerian two-phase flow model to scour processes

In this paper, the application of a two-phase flow model to scour processes is presented. The model is first calibrated against experimental data of unidirectional sheet-flow (one-dimensional configuration). The model is then applied to multi-dimensional configurations for the scour under a submarine pipeline and around a vertical pile. The results show that quantitative results can be obtained at the upstream sides of structures, the lee-wake erosion driven by the vortex shedding deserves further research.

Numerical Investigation of Solitary Wave Interaction with Double Row of Vertical Slotted Piles

Numerical Investigation of Solitary Wave Interaction with Double Row of Vertical Slotted Piles

Bočna nosivost i pomeranja vertikalnih šipova opterećenih horizontalnim silama

Bočna nosivost i pomeranja vertikalnih šipova opterećenih horizontalnim silama

Influence of pile radius on the pile head kinematic bending strains of end-bearing pile groups

An analytical solution is developed for the kinematic response of a group of end-bearing fixed-head cylindrical vertical piles embedded in a homogeneous elastic stratum subjected to vertically-propagating harmonic shear waves. Pile-soil interaction, incorporating group effects in a pile group, is represented through a simplified beam-on-dynamic-Winkler-foundation (BDWF) model with realistic frequency-dependent springs and dashpots. Expressions for interaction factors and curvature ratios atop the foundation are presented considering different boundary conditions at the tip of the piles. To investigate the fundamental characteristics of kinematic bending in end-bearing pile groups when kinematic interaction dominates, kinematic bending strains at the head of each pile are expressed in terms of the slenderness ratio. The methodology is verified by comparison against results of a coupled finite element-boundary element (FE-BE) model. Obtained results indicate that kinematic bending strains of end-bearing single piles and piles in a group follow the same trend, with values being almost coincident in the case of slender piles. In addition, boundary conditions at the pile tip markedly affect the kinematic bending at the pile head.

A Novel Approach for the Optimal Design of a Vertical Cellular Breakwater Based on Multi-Objective Optimization

In this paper, a methodology based on multi-objective optimization is proposed for the optimal design of a vertical cellular breakwater, consisting of prefabricated rectangular cells with two vertical permeable walls supported by two rows of vertical circular piles. The vertical wall consists of a perforated upper part and a lower part with horizontal slots. Maximization of wave energy dissipation coefficient and minimization of the volume of material used in the breakwater are the two objectives considered. The methodology employed in this study uses a theoretical model to determine the wave energy dissipation coefficient and material volume in the vertical cellular breakwater. The most widely used and acceptable eigenfunction expansion method is employed to evaluate the hydrodynamic coefficients of breakwater. The results obtained by the eigenfunction expansion method is evaluated by conducting experiments and by comparing with the published results. The two objectives to be achieved in the design are conflicting and it is quite difficult to satisfy both the objectives simultaneously. A multi-objective optimization tool based on genetic algorithm (GA) is employed to find the pareto optimal set of solutions in a search space. To arrive at the best-agreed solution from the obtained pareto optimal set of solutions, some practical preferences are considered. Results indicate that this approach can be effectively applied for the optimal design of a vertical cellular breakwater.

Modeling of Oblique Load Test on Batter Pile Group Based on Support Vector Machines and Gaussian Regression

This paper evaluates the potential of two machine learning approaches i.e. Support vector machine (SVR) and Gaussian processes (GP) regression to model the oblique load capacity of batter pile groups. Linear regression was used to compare the performance of both SVR and GP based regression approaches to model the oblique load. Data set used consists of 147 samples obtained from the laboratory experiments. Out of the total sample size, 105 randomly selected samples were used for training whereas remaining 42 were used for testing the models. Input data set consist of angle of oblique load, pile length, sand relative density, number of vertical piles, number of batter piles where as oblique load was considered as output. Two kernel functions i.e. Polynomial and radial based kernel function were used with both SVR and GP regression. A comparison of results suggest that radial basis function based SVR approach works well in comparison to GP and linear regression based approaches and it could successfully be employed in modelling the oblique load capacity of batter pile groups. Parametric analysis and sensitivity analysis suggest that loading angle, pile length and number of batter pile were important in prediction of oblique load.

Dynamic lateral response of under-reamed vertical and batter piles

Dynamic lateral response of three under-ream reinforced concrete piles constructed in silty sand {vertical, P1 (β = 0°); and batter piles P2 (β = 10°) and P3 (β = 20°)} having equal length of 2.5 m, shaft diameter 0.2 m and under-ream bulb of diameter 0.5 m were considered for this experimental study. Dynamic loads were generated using an oscillator motor assembly mounted on top of pile cap and the response of these piles were recorded in real time using three accelerometers placed along the depth of the pile cap. These piles were subjected to varying dynamic load by changing the eccentricity setting of the oscillator in the frequency range of 0–40 Hz. The test results show that the resonant frequency of the soil-pile system decreases; and peak lateral displacement increases with increase in the force level. The variation of rotational stiffness and the damping ratio of the soil-pile system with force level did not follow a clear trend. Thus the presence of an under-ream bulb in a batter pile does not have a significant influence on the lateral behaviour of batter piles.

Influence of seismic motions on behavior of piles in liquefied soils

SummaryIn the present study an analytical procedure based on finite element technique is proposed to investigate the influence of vertical load on deflection and bending moment of a laterally loaded pile embedded in liquefiable soil, subjected to permanent ground displacement. The degradation of subgrade modulus due to soil liquefaction and effect of nonlinearity are also considered. A free headed vertical concrete elastic nonyielding pile with a floating tip subjected to vertical compressive loading, lateral load, and permanent ground displacement due to earthquake motions, in liquefiable soil underlain by nonliquefiable stratum, is considered. The input seismic motions, having varying range of ground motion parameters, considered here include 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj, and 2011 Sikkim motions. It is calculated that maximum bending moment occurred at the interface of liquefiable and nonliquefiable soil layers and when thickness of liquefiable soil layer is around 60% of total pile length. Maximum bending moment of 1210 kNm and pile head deflection of 110 cm is observed because of 1995 Kobe motion, while 2001 Bhuj and 2011 Sikkim motions amplify the pile head deflection by 14.2 and 14.4 times and bending moment approximately by 4 times, when compared to nonliquefiable soil. Further, the presence of inertial load at the pile head increases bending moment and deflection by approximately 52% when subjected to 1995 Kobe motion. Thus, it is necessary to have a proper assessment of both kinematic and inertial interactions due to free field seismic motions and vertical loads for evaluating pile response in liquefiable soil.

DEVELOPMENT AND PROSPECT OF ROOT PILES IN TUNNEL FOUNDATION REINFORCEMENT

Over the past couple of decades, root piles as the new tool for addressing a number of tough problems have been gaining a continually increasing interest in tunnel, especially for complex geological conditions. Therefore, in order to promote the development and application of root piles in tunnel engineering, this paper systematically sorts out the research status and development prospect of root piles from the application in foundation underpinning to reinforcement of tunnel foundation. Firstly, the type and development process of root piles are discussed. Secondly, the reinforcement mechanism of the root piles in the tunnel base is refined and combed: the reinforcement mechanism analysis focuses on frictional resistance of soil around pile, soil among piles, and piles. Thirdly, the calculation method of reinforced tunnel foundation is studied from the bearing of vertical load, horizontal load and pile reinforcement design. And through the engineering case, the paper illustrates the reinforcement effect of the root pile in ensuring the stability of the tunnel and the concrete process of the root piles in the tunnel construction. Finally, the problem and development prospect of root piles are discussed, so as to provide new perspectives and fundamental data for the research on tunnel engineering.

Stabilisation of excavated slopes in strain-softening materials with piles

The use of a row of discrete vertical piles is an established method, successfully used to remediate failure of existing slopes and to stabilise potentially unstable slopes created by widening tran...

Briefing: Maritime Structures – the design of challenging vertical pile dolphin solution

The demand for energy in Southeast Asia and the Pacific region has resulted in vast growth in gas exploration across the continent of Australia. With the approval for a number of liquefied natural gas (LNG) export facilities across the Australian seaboard, Arup Australasia has put its multi-disciplinary capabilities to full use in the delivery of a number of LNG jetties in Gladstone, Queensland in a design and construct collaboration with the contractor John Holland Group (JHG). This paper presents the design and construction of the dolphin structures, which were the result of close collaboration between JHG and Arup. The goal of this paper is to describe the importance of early constructability considerations and the complex interface between maritime, geotechnical and structural disciplines. The paper outlines the inputs and the consideration of both berthing and mooring dolphins designed to accommodate berthing and mooring of vessels of up to 220 000 m3 capacity. The approach of the paper is to describe the design solution in broad terms and selected key aspects in detail.

Probabilistic analysis of piled earth platform under concrete floor slab

This paper proposes a two-dimensional axisymmetric numerical modelling of an earth platform over a clayey sand improved by stiff vertical piles using a finite-difference continuum approach. The study focuses on the surface settlements and the stress efficacy of the improvement system. Only the soil parameters are considered as random variables and two assumptions (normal distribution or non-normal distribution) are used. The first-order reliability method (FORM) is applied to calculate the reliability index. Response surface methodology (RSM) allows for access to the Hasofer-Lind reliability index and is optimized by the use of a genetic algorithm. The Hasofer-Lind reliability index is calculated for two distinct cases. Firstly, only the geomechanical parameters of the clayey sand are considered as random variables; secondly, the parameters of both the clayey sand and the earth platform are considered. The results show that the reliability of a single soil layer is safer than the reliability of the whole system.

Numerical study of irregular breaking wave forces on a monopile for offshore wind turbines

The substructures of offshore wind turbines are subjected to different types of hydrodynamic loads from sea states. The wave forces exerted by irregular breaking waves are one of the serious concerns because of the uncertainties involved in defining the breaking wave and the resulting force calculations. In the present study, irregular breaking wave forces on a vertical pile structure are investigated using an open-source Computational Fluid Dynamics (CFD) model REEF3D. The Level Set Method (LSM) is used for modelling the free surface. The Bretschneider spectrum is used for the irregular wave generation. This is validated in the numerical wave tank by comparing the numerical wave spectrum with the experimental wave spectrum. The wave free surface is calculated at three wave gauge locations and compared with experiments. It is observed that the peak of spectral wave density is higher for the wave gauge located besides the cylinder due to shoaling, wave run up and reflections from the cylinder and the peak of spectral wave density is lower for the wave gauge located behind the cylinder due to wave breaking. Further, simulations are performed to study the wave forces on a monopile due to the depth-limited breaking waves. A good match is observed with the experimental and numerical results. Numerical wave energy spectra at different locations along the tank are compared to study the changes in the wave surface elevations due to the interaction of irregular breaking waves with a monopile. The statistical parameters for free surface elevation and wave forces are further investigated. The free surface features around the monopile during its interaction with waves are also studied.

A Three Dimensional Comparative Study of Seismic Behaviour of Vertical and Batter Pile Groups

To a practicing foundation engineer, the performance of batter pile under seismic conditions still remains a questionable prospect. The contradictory findings reported by various investigators with regard to the performance of batter piles add to this dilemma. This calls for a rigorous three-dimensional investigation to evaluate seismic behavior of batter pile groups. In this study, a comparative assessment of three-dimensional seismic behavior of a 2 × 2 vertical and batter pile groups having batter angle of 15° was carried out using a full three-dimensional finite element code developed in MATLAB (Sarkar 2009). The effects of centre to centre spacing of piles and soil modulus values were investigated. Idealized soil profiles having constant and triangular variation of soil modulus were adopted for the study. Results of analyses for both the vertical and batter pile groups are presented in terms of dynamic stiffness and kinematic interaction factors. Results indicate better seismic performance of batter pile groups in comparison to that of vertical pile groups. To demonstrate the importance of the findings, a five-storied portal frame structure supported separately on vertical and batter pile groups were considered and analyzed for El-Centro Earthquake (1940) time history. The difference in structural response considering vertical and batter pile groups is highlighted.

A numerical procedure to correlate the subgrade reaction coefficient with soil stiffness properties for laterally loaded piles using the FSAFEM

The soil subgrade coefficient is a significant parameter in the Winkler model which is usually required in the practical design of piles against lateral loads. However, the accurate assessment of this coefficient is often difficult to establish, consequently, the most obvious way to reach appropriate values of ks seems to find correlations with soil stiffness properties: the Young’s modulus and the Poisson's ratio that cause predictions match more rigorous elasticity results. Since the problem of a vertical pile under horizontal loading is geometrically axisymmetric but the loading is non-axisymmetric, it is convenient to employ a finite element procedure known as Fourier Series Aided Finite Element Analysis to handle this problem including the soil/pile interface states. The methodology followed in this paper has been cast into two major steps. Firstly, and in order to obtain a correlation between ks and soil deformation properties Es and νs in the form of analytical equations expressed in a dimensionless factor , a pile segment at the centre of a thin slice from the soil/pile system is displaced horizontally and the soil reaction is back-figured in function of various outer boundaries of the modelled medium. Secondly, the analytical formulae obtained along with other proposed expressions collected from the literature have been implemented in an existing Winkler model computer code. Then, piles with two different slenderness ratios ( and 20) under both horizontal force an overturning moment in a homogeneous soil where two pile/soil interface states have been studied by Winkler models as well as by a full finite element semi-analytical approach. Results of the parametric study showed that the drawbacks of the Winkler model are not due to the inaccuracy in the stiffness of springs used to model the soil, but to the model itself which ignores the transfer of shear stresses between the soil layers.

Three-dimensional propagation of waves in piles during low-strain integrity tests

In this note the concept of discretising the pile into virtual parts is introduced in order to derive an analytical solution that describes three-dimensional propagation of waves in piles during low-strain integrity tests, considering both vertical and radial pile displacements. The effect of transverse wave propagation on the results is quantified by comparing the proposed solution against a previously published method in which only vertical displacement was considered, results of dynamic numerical analyses, as well as the classical one-dimensional solution. Using the obtained waveforms, an attempt is made to identify and describe the mechanisms of three-dimensional propagation of longitudinal waves in piles, and how these may affect the interpretation of low-strain integrity tests.

Modeling of Batter Pile Behavior under Lateral Soil Movement

Pile foundation is frequently used when structures are located on weak sublayers or are at risk from lateral loadings such as earthquakes. The design of pile foundations has recently become crucial to stop slope movement. To understand the behavior of pile foundations subjected to lateral soil movement, the three-dimensional Fast Lagrangian Analysis of Continua (FLAC3D) program was used to perform numerical simulations, which can reduce the cost of field testing. Vertical piles and batter piles were combined into 3 × 3 pile groups, and the response of batter piles to soil movement was analyzed. The outer batter piles led to an increased bending moment in the middle, vertical pile row. Increasing the pile spacing and the presence of battered piles reduced the pile group’s displacement. The batter pile group’s maximum bending moment was smaller than the vertical pile group’s in sand soil, but 5–8 times higher in clay soil.

Numerical simulation of scour and backfilling processes around a circular pile in waves

This study continues the investigation of flow and scour around a vertical pile, reported by Roulund et al. (2005). Flow and scour/backfilling around a vertical pile exposed to waves are investigated by using a three-dimensional numerical model based on incompressible Reynolds averaged Navier–Stokes equations. The model incorporates (1) k-ω turbulence closure, (2) vortex shedding processes, (3) sediment transport (both bed and suspended load), as well as (4) bed morphology. The numerical simulations are carried out for a selected set of test conditions of the laboratory experiments of Sumer et al. (1997, 2013a), and the numerical results are compared with those of the latter experiments. The simulations are carried out for two kinds of beds: rigid bed, and sediment bed. The rigid-bed simulations indicate that the vortex shedding for waves around the pile occurs in a “one-cell” fashion with a uniform shedding frequency over the height of the cylinder, unlike the case for steady current where a two-cell structure prevails. The rigid-bed simulations further show that the horseshoe vortex flow also undergoes substantial changes in waves. The amplification of the bed shear stress around the pile (including the areas under the horseshoe vortex and the lee wake region) is obtained for various values of the Keulegan-Carpenter number, the principal parameter governing the flow around the pile in waves. The present model incorporated with the morphology component is applied to several scenarios of scour and backfilling around a pile exposed to waves. In the backfilling simulations, the initial scour hole is generated either by a steady current or by waves. The present simulations indicate that the scour and backfilling in waves are solely governed by the lee-wake flow, in agreement with observations. The numerical model has proven successful in predicting the backfilling of scour holes exposed to waves. The results of the numerical tests indicate that the equilibrium depth of scour holes is the same for both the scour and the backfilling for a given Keulegan-Carpenter number, in full agreement with observations.

On the behaviour of pile groups under combined lateral and vertical loading

The effect of vertical loads on the lateral response of a 3×5 pile group embedded in sandy and clayey soils is studied through 3D finite differences analyses using the computer code FLAC3D. In the numerical model, the piles were treated as a linear elastic material and the soil was idealized using the Mohr-Coulomb constitutive model with a non-associated flow rule. Vertical loads, inducing a vertical pile head displacement of 0.01-pile diameter, were applied prior to the application of the lateral loads. Numerical results showed that the lateral resistances of the piles installed in sandy soil increase with vertical loads. However, the presence of vertical loads on piles embedded in clay reasonably decreases their lateral capacities. The increase and decrease in the lateral stress in the sandy and clayey soils, respectively, are the major driving factors to contribute the change in the lateral resistance of piles, depending on the pile position in the group and its lateral deflection. The distribution of lateral loads among piles in the group tends to be more uniform when vertical loads were considered leading to a more economical pile foundation design.

Prediction of vertical pile capacity of driven pile in cohesionless soil using artificial intelligence techniques

Piles are used in substructures of different infrastructural constructions. Due to the complex nature of soil, there are different empirical models to predict the bearing capacity of piles. The objective of the present study is to develop prediction models for vertical loaded driven piles in cohesionless soil using a novel artificial intelligence (AI) technique multi-objective genetic programming (MOGP). Two other recent AI techniques, multivariate adaptive regression spline (MARS) and functional network (FN), are also used to compare the efficacy of different AI techniques. The results MOGP, MARS and FN models are compared in terms of different statistical parameters such as correlation coefficient (R), absolute average error, root-mean–square-error, overfitting ratio and P50. A ranking criteria approach has been implemented to assess the performance of the prediction models developed in this study along with other AI and empirical models available in the literature. The predictive model equations based on the MOGP, MARS and FN are also presented.