Piles In Clay Research Articles

Spatial Probabilistic Model of Block Failure Capacity of Piles in Clay

Spatial Probabilistic Model of Block Failure Capacity of Piles in Clay

Ultimate bearing capacity of laterally loaded piles in clay – Some practical considerations

The paper re-visits the topic of ultimate bearing capacity of laterally loaded piles in clay. The paper first presents a review of various recommendations made by design guidelines and industry practitioners which illustrates inconsistency and need for further work. A literature study is therefore performed and a generalised recommendation of the ultimate lateral capacity of piles in clay that is self-consistent and flexible for a wide range of conditions is made. The paper further investigates two practical considerations often encountered in design, namely the effect of axial loading and the effect of soil strength anisotropy by means of finite element analyses. Practical methods to account for these effects are proposed.

Nonlinear Analysis of Single Laterally Loaded Piles in Clays Using Modified Strain Wedge Model

This paper proposes a modified strain wedge (MSW) model for nonlinear analysis of laterally loaded single piles in clays. The MSW model is used to calculate the soil resistance under increasing pile deflection. The stress–strain behavior of clays in the MSW, which is needed to calculate the soil resistance, is described in terms of both hyperbolic and bilinear stress–strain relationships. The subgrade reaction modulus of soil below the MSW is assumed to equal the conventional subgrade reaction modulus and to remain constant under the lateral loading of the pile. The applicability of the proposed model was verified by eight case histories. The results indicate that (1) the predicted results are consistent with the measurements for all eight full-scale tested piles; (2) the bilinear stress–strain relationship is not recommended for clays because the clays usually have a large e50 and, thus, they exhibit a linear behavior in the MSW during loading; (3) the predicted pile response is less sensitive to the effective friction angle than to the undrained shear strength; and (4) the proposed MSW model applies to normally consolidated clays and to overconsolidated clays until they reach their peak strength.

Influence of vertical loads on lateral response of pile foundations in sands and clays

Although the load applied to pile foundations is usually a combination of vertical and lateral components, there have been few investigations on the behavior of piles subjected to combined loadings. Those few studies led to inconsistent results with regard to the effects of vertical loads on the lateral response of piles. A series of three-dimensional (3D) finite differences analyses is conducted to evaluate the influence of vertical loads on the lateral performance of pile foundations. Three idealized sandy and clayey soil profiles are considered: a homogeneous soil layer, a layer with modulus proportional to depth, and two-layered strata. The pile material is modeled as linearly elastic, while the soil is idealized using the Mohr–Coulomb constitutive model with a non-associated flow rule. In order to confirm the findings of this study, soils in some cases are further modeled using more sophisticated models (i.e. CYsoil model for sandy soils and modified Cam-Clay (MCC) model for clayey soils). Numerical results showed that the lateral resistance of the piles does not appear to vary considerably with the vertical load in sandy soil especially at the loosest state. However, the presence of a vertical load on a pile embedded in homogeneous or inhomogeneous clay is detrimental to its lateral capacity, and it is unconservative to design piles in clays assuming that there is no interaction between vertical and lateral loads. Moreover, the current results indicate that the effect of vertical loads on the lateral response of piles embedded in two-layered strata depends on the characteristics of soil not only surrounding the piles but also located beneath their tips.

Ultimate lateral capacity of two dimensional plane strain rectangular pile in clay

This paper presents a new numerical solution of the ultimate lateral capacity of rectangular piles in clay. The two-dimensional plane strain finite element was employed to determine the limit load of this problem. A rectangular pile is subjected to purely lateral loading along either its major or minor axes. Complete parametric studies were performed for two dimensionless variables including: (1) the aspect ratios of rectangular piles were studied in the full range from plates to square piles loaded along either their major or minor axes; and (2) the adhesion factors between the soil-pile interface were studied in the complete range from smooth surfaces to rough surfaces. It was found that the dimensionless load factor of rectangular piles showed a highly non-linear function with the aspect ratio of piles and a slightly non-linear function with the adhesion factor at the soil-pile interface. In addition, the dimensionless load factor of rectangular piles loaded along the major axis was significantly higher than that loaded along the minor axis until it converged to the same value at square piles. The solutions of finite element analyses were verified with the finite element limit analysis for selected cases. The empirical equation of the dimensionless load factor of rectangular piles was also proposed based on the data of finite element analysis. Because of the plane strain condition of the top view section, results can be only applied to the full-flow failure mechanism around the pile for the prediction of limiting pressure at the deeper length of a very long pile with full tension interface that does not allow any separation at soil-pile interfaces.

Study on the applicability of a retaining wall using batter piles in clay

A retaining wall using batter piles has been developed and studied to improve existing earth-retaining structures at Pusan National University. The earth-retaining method is a temporary excavation method using an integrated system of front supports and batter piles. The batter piles connected to the front supports significantly reduce the earth pressure acting on the front supports by distributing it to batter piles to increase structural stability. In this study, the existence of batter piles, the fixity of the tips of front supports or batter piles, the spacing between batter piles, and the verticality of front supports are varied across model tests. The lateral displacement of the earth-retaining wall decreased by approximately 40% and 15% for the existence and fixity of batter piles, respectively. The applicability of the earth-retaining method using batter piles has been verified with finite element analysis and field test execution in clay ground.

Evaluation of Curve Fitting Techniques in Deriving p–y Curves for Laterally Loaded Piles

The p–y method is one of the most popular methods for the analysis and design of laterally loaded piles. The mathematical relationship it provides between the bending moment, which can be easily measured at strain gauges along the pile, and the soil resistance and lateral pile displacement, facilitates the construction of p–y curves. Numerical techniques are required to fit smooth continuous curves to the discrete bending moment data in order to improve the accuracy of subsequent differentiation and integration operations. Due to the lack of guidance on the optimum positioning of strain gauges and the reliability and accuracy of curve fitting methods, a unifying study, inclusive of small (0.61 m) and large (3.8 and 7.5 m) diameter piles in clay, was carried out using 18 strain gauge layouts and cubic spline, cubic to quintic B-spline and 3rd to 10th degree global polynomial techniques. Bending moment data was obtained using 3D finite element analysis. Through a comprehensive evaluation, the cubic and cubic B-spline methods were found to be consistently accurate in deriving p–y curves for both the small and large diameter piles.

Numerical simulation of plug formation during casing installation of cast-in-place concrete pipe (PCC) piles

There is a historic lack of research examining inner soil plugging and outer lateral soil deformation during installation of pipe piles in clay. Furthermore, the influence of the pile tip geometry on soil deformation has not been investigated. Cast-in-place concrete pipe (PCC) piles are a recent generation of pipe piles for soft ground improvement applications, and are cast in place using an innovative double-walled steel casing with a tapered tip. This paper investigates the effect of tip geometry on soil flow mechanisms inside and outside the PCC pile casing during installation in clay. Large-deformation finite element (LDFE) analysis was conducted simulating the continuous penetration process of the casing installation. The LDFE results were validated against (i) field monitoring data in terms of soil lateral displacement and heave outside the casing and (ii) centrifuge test data in terms of penetration resistance, with excellent agreement obtained. An extensive parametric study was then performed encompassing a practical range of parameters. The geometry of the casing tip was shown to have significant influence on the soil movements inside and outside the casing, but minimal effect on the casing penetration resistance. The optimal tapered tip with a tip angle of 45° and minimal extended tip length beneath the tip angle allowed more soil to be pushed inside the casing and less lateral displacement outside the casing, which dictates the amount of concrete required to fill the cavity inside the pile and the pile construction sequence, respectively. Design expressions are proposed for estimating soil movements inside and outside the casing with optimal tip geometry being installed.

Prediction of friction capacity of driven piles in clay using artificial intelligence techniques

Driven piles are widely used due to their easy installation set up and are economical. In this paper, prediction models for predicting friction capacity of piles in clay soils based on experimental test results are developed using two recently developed artificial intelligence techniques; multivariate adaptive regression splines (MARS) and functional networks (FN). The efficacy of developed MARS and FN models has been compared with previously developed models as given in the literature in terms of statistical parameters like correlation coefficient (R), Nash–Sutcliffe coefficient of efficiency (E), absolute average error, maximum average error, root mean square error and normalised mean bias error. Based on statistical performances, MARS and FN models are found to have a better predictive capacity than existing models.

Discussion of “Ultimate Shaft Friction and Load-Displacement Response of Axially Loaded Piles in Clay Based on Instrumented Pile Tests” by Kjell Karlsrud

Discussion of “Ultimate Shaft Friction and Load-Displacement Response of Axially Loaded Piles in Clay Based on Instrumented Pile Tests” by Kjell Karlsrud

Closure to “Ultimate Shaft Friction and Load-Displacement Response of Axially Loaded Piles in Clay Based on Instrumented Pile Tests” by Kjell Karlsrud

Closure to “Ultimate Shaft Friction and Load-Displacement Response of Axially Loaded Piles in Clay Based on Instrumented Pile Tests” by Kjell Karlsrud

Analysis of Suction Piles for Mooring Floating StructureFoundations in Clay Soil at Deepwater Levels

Oil and gas exploration is increasingly moving to deepwater locations to meet the increasing energy demands. In this environment, floating structures with suction pile foundations are commonly used because their cost-effectiveness. Some studies have been conducted to examine the behavior of suction piles in clay soils, but the typical clay conditions considered are normally consolidated and lightly over-consolidated. In this paper, the behavior of suction piles in under-consolidated clays and under-consolidated, normally consolidated clays, as extracted from actual deepwater soil conditions. The evaluation was performed using geotechnical 3D finite element software Plaxis. Suction piles with two different aspect ratios (L/D = 2 and 6) were considered, and the focus was on the effect of load angles (0 to 90) and the effects of pad-eye positions (0.5 L to 0.9 L). For short piles, the load angles had a relatively insignificant effect on the overall ultimate resistance, while for long piles, the angles affected the overall resistance considerably with a decrease in resistance up to approximately 50 percent. This different behavior could be explained from the observed pile deformation patterns. The pad-eye positions affected the pile resistances significantly as well with a decrease in the resistance factor up to about 30 percent. Nevertheless, it can be concluded that the overall behavior of suction piles in combined clay conditions is practically similar to that of piles in normally consolidated and over-consolidated clays.

점성토 지반에 근입된 그룹 석션파일에 대한 비선형 스프링 모델링 기법 개발

Recently, several researches on the development of new economical anchor systems have been performed to support floating structures. This study focused on the group suction piles, which connect mid-sized suction piles instead of a single suction pile with large-diameter. The group suction pile shows the complex bearing behavior with translation and rotation, so it is difficult to apply conventional design methods. Therefore, the numerical modeling technique was developed to evaluate the horizontal bearing capacity of the group suction piles in clay. The technique models suction piles as beam elements and soil reaction as non-linear springs. To analyze the applicability of the modeling, the horizontal load-movement curves of the proposed modeling were compared with those of three-dimensional finite element analyses. The comparison showed that the modeling underestimates the capacity and overestimate the displacement corresponding to the maximum capacity. Therefore, the correction factors for the horizontal soil resistance was proposed to match the bearing capacity from the three-dimensional finite element analyses.

Prediction of Lateral Load Capacity of Pile in Clay Using Multivariate Adaptive Regression Spline and Functional Network

This paper discusses the use of multivariate adaptive regression splines (MARS) and functional networks (FN) for prediction of the lateral load capacity of piles in clay. The results obtained from MARS and FN have been compared with different empirical models and artificial neural network in terms of statistical parameters such as correlation coefficient (R), Nash–Sutcliff coefficient of efficiency (E), absolute average error, maximum average error and root mean square error. Based on the statistical parameters, MARS and FN were found to have a better predictive capacity. Predictive equations are provided based on the MARS and FN model. A sensitivity analysis is also presented to determine the importance of inputs in prediction of the lateral load capacity of piles.

Lateral Load Capacity of Piles in Clay Using Genetic Programming and Multivariate Adaptive Regression Spline

This study presents the development of predictive models of lateral load capacity of pile in clay using artificial intelligence techniques; genetic programming and multivariate adaptive regression spline. The developed models are compared with different empirical models, artificial neural network (ANN) and support vector machine (SVM) models in terms of different statistical criteria. A ranking system is presented to evaluate present models with respect to above models. Model equations are presented and are found to be more compact compared to ANN and SVM models. A sensitivity analysis is made to identify the important inputs contributing to the lateral load capacity of pile.

Shear Zone around Jacked Piles in Clay

AbstractAs the most important feature of jacked open-ended concrete pipe piles, shear zone has fluence of crucial importance during installing and after penetration. This study conducted a field test in silt deposit to observe the physical phenomenon of shear zone after installation and investigated soil parameter differences from undisturbed soil through laboratory tests. Direct observation on shear zone reveals that the boundary between shear zone and in situ soil is evident. The average soil thickness in the shear zone falls between 6 and 30 mm, which are closely related to natural water content and void ratio in different layers. Laboratory tests on the shear zone show evident compaction during installation, and the soil parameters in the shear zone are sensitive to the jacking installation procedure. Some soil parameters decrease, whereas others increase because of excess pore water dissipating after installation. The extent of the shear zone is helpful in understanding interface friction on pretensi...

Ultimate Shaft Friction and Load-Displacement Response of Axially Loaded Piles in Clay Based on Instrumented Pile Tests

AbstractNew semiempirical design procedures for the determination of ultimate shaft friction and load-displacement response of axially loaded piles in clay are proposed. A main basis for developing the new procedures was detailed review and reassessment of results from a series of pile load-test programs published over the past 30 years on piles well instrumented to monitor soil and pore pressures as well as load distribution along the pile shafts. Two new alternative procedures are proposed for predicting the ultimate shaft friction: an α approach, which uses the normalized undrained strength based on direct simple shear tests as a main correlation parameter, and a β approach, which uses the overconsolidation ratio (OCR). Both approaches include the effects of the plasticity index of the clay, Ip, which is shown to have an especially large impact on the correlations when Ip<25%. In practical design, it is recommended that both methods be used and design values be selected for the ultimate shaft friction ...

Variation of limiting lateral soil pressure with depth for pile rows in clay

Pile group interaction effects on the lateral pile resistance are investigated for the case of a laterally loaded row of piles in clay. Both uniform undrained shear strength and linearly increasing with depth shear strength profiles are considered. Three-dimensional finite element analyses are presented, which are used to identify the predominant failure modes and to calculate the reduction in lateral resistance due to group effects. A limited number of two-dimensional analyses are also presented in order to examine the behaviour of very closely spaced piles. It is shown that, contrary to current practice, group effects vary with depth; they are insignificant close to the ground surface, increase to a maximum value at intermediate depths and finally reduce to a constant value at great depth. The effect of pile spacing and pile–soil adhesion are investigated and equations are developed for the calculation of a depth dependent reduction factor, which when multiplied by the limiting lateral pressure along a single pile, provides the corresponding variation of soil pressure along a pile in a pile row. This reduction factor is used to perform p–y analyses, which show that, due to this variation of group effects on the lateral soil pressures with depth, the overall group interaction effects depend on the pile length. Comparisons are also made with approaches used in practice that assume constant with depth reduction factors.

Closure to “Pile Setup in Cohesive Soil. I: Experimental Investigation” by Kam W. Ng, Matthew Roling, Sherif S. AbdelSalam, Muhannad T. Suleiman, and Sri Sritharan

Closure to “Pile Setup in Cohesive Soil. I: Experimental Investigation” by Kam W. Ng, Matthew Roling, Sherif S. AbdelSalam, Muhannad T. Suleiman, and Sri Sritharan

Prediction of lateral load capacity of piles using extreme learning machine

This study presents the development of a predictive model for the lateral load capacity of pile in clay using an artificial intelligence technique, extreme learning machine (ELM). Other artificial intelligence models like artificial neural networks (ANN) (Bayesian regularization neural network (BRNN), differential evolution neural network (DENN)) are also developed to compare the ELM model with them and available empirical models in terms of different statistical criteria. A ranking system is presented to evaluate the present models for identifying the “best” model. Sensitivity analyses are made to identify important inputs contributing to the developed models.