Single Piles In Sand Research Articles

Ultimate Lateral Resistance of Single Piles in Sand

The p-y curve method is currently the most widely utilized analytical approach for horizontally loaded piles. Precisely determining the ultimate soil resistance is essential to enhance the accuracy of the p-y curve. Despite various scholars proposing methods to establish the law governing ultimate soil resistance with soil depth in the sand, significant discrepancies exist among these approaches. This paper posits that the three-dimensional failure mode of the shallow soil in front of the pile manifests as a cone when it reaches the limit state. The expression for the ultimate soil resistance of a single pile in shallow soil is derived through limit equilibrium theory, and subsequently, the modified p-y curve is obtained. The accuracy was validated through a comparison between the corrected p-y curve and results obtained from centrifugation experiments and field studies. In contrast to the API specification method, the refined hyperbolic function p-y curve demonstrates enhanced precision, facilitating precise predictions of pile head displacement and pile bending moments under horizontal loads.

Geotechnical behavior of a single pile in sand with varied cross-section geometries and construction techniques

Geotechnical behavior of a single pile in sand with varied cross-section geometries and construction techniques

Utilization of enlarged base to improve the uplift capacity of single pile in sand—model study

Utilization of enlarged base to improve the uplift capacity of single pile in sand—model study

Analysis of lateral behaviour of monopiles considering principal stress rotation under coupled loading in sand

Monopiles for offshore wind turbine foundations are often subjected to vertical-horizontal combined loading. For the analysis of piles subjected to horizontal loads in sand, the p-y curve method based on the Winkler model is usually employed, where p is the soil resistance of the pile per unit length and y is the local horizontal displacement of the pile or the soil compression at the point of study. As the load bearing properties of horizontally loaded piles depend on the ultimate resistance P u of the soil around the pile in the shallow soil layer, it is important to determine P u of the shallow soil accurately. In this paper, the wedge model is employed to calculate P u. The effect of vertical shear stress along the pile on the principal stress direction which decides the bottom angle of the wedge is taken into account. Then, the effects of the vertical loads on the p-y curves, P-Δ effect, M R effect is considered in the horizontal equilibrium equation of the pile. The shear-displacement method is employed to calculated the vertical responses of the pile. The shear stress and horizontal soil resistance were redistributed when the coupled effect of the vertical load and the horizontal load is considered. Then, the horizontal responses of the monopile under vertical load, horizontal load and moment simultaneously can be calculated. Finally, the proposed method is used to calculate a centrifuge model test where a piles is subjected to coupled loads in sandy soils. The results showed that the pile moment curve after considering the bottom angle of the wedge β modification is closer to the experimental results than without the β modification, so it makes the modified β more reasonable in analyzing the behavior of laterally loaded single piles in sand. At the same time, the β modification is not required for pure horizontal loading.

Research on uplift model test of single pile in sand

This paper mainly uses the method of model test to study the ultimate uplift bearing characteristics of a single pile with different length-to-diameter ratios, mainly from the distribution laws of the uplift bearing capacity of the pile, the axial force of the pile and the side friction of the pile perform analysis. The model pile is made of PVC pipe, and resistance strain gauges are attached to both sides of the pipe. The strain value of the PVC pipe under different load conditions is measured to obtain the working behavior of the pile during the process of pulling out the pile. The result shows that the model test data is in good agreement with the numerical simulation.

Experimental and Numerical Analysis on the Rate-Dependent Cyclic Lateral Load on a Single Pile in Sand

Experimental and Numerical Analysis on the Rate-Dependent Cyclic Lateral Load on a Single Pile in Sand

Experimental study and theoretical analysis on impact characteristics of single pile

The impact characteristics of a single pile are the theoretical basis of the high-strain detection technology of piles and pile driving. Firstly, a series of pile model experiments are conducted to study the characteristics of single pile penetration, axial force and friction of the pile under impact loads of different rammer loads and falling distances. Then, the dynamic model of a single pile under impact load under the condition of pile-soil slippage was established by using the elastodynamic method, and the analytical solution of the pile axial force was obtained. The results show that the theoretical solution is in good agreement with the model test results. This shows that the completely bonded model without considering slippage overestimates the frictional resistance between the pile and soil, and the pile-soil slippage model can better simulate the impact of a single pile in sand.

A Centrifuge Modelling and Finite Element Analysis of Laterally Loaded Single Piles in Sand with Focus on P–Y Curves

Centrifuge modelling and finite element analysis are powerful tools of research on the lateral pile/soil interaction. This paper aims at presenting the main results of experimental and numerical analysis of the pile response under monotonic lateral loading in sand. After description of the experimental devices, it focuses on the determination of the load-transfer P-Y curves for rigid and semi-rigid piles embedded in dry dense sand by using the experimental bending moment profiles obtained in centrifuge tests, as well as by a three-dimensional finite element models using ABAQUS Software. The elastic perfectly plastic Mohr-Coulomb constitutive model has been used to describe the soil response, and the surface-to-surface contact method of ABAQUS software has been used to take into account the nonlinear response at soil/pile interface. The analysis methodology has allowed to propose a hyperbolic function as a model to construct P-Y curves for rigid and semi-rigid piles embedded in dry dense sand, this model is governed by two main parameters, which are the initial subgrade reaction modulus, and the lateral soil resistance, the latter has been formulated in terms of Rankine’s passive earth pressure coefficient, the sand dry unit weight, and the pile diameter.

Centrifuge Modeling of Single Piles in Sand Subjected to Dip-Slip Faulting

AbstractPrevious studies have found that pile foundations will be severely damaged when subjected to faulting. However, the pile–soil interaction mechanism is still unclear due to the lack of well-...

Influence mechanism of vertical-horizontal combined loads on the response of a single pile in sand

Pile foundations are used to support both vertical and horizontal loads in many geotechnical projects, such as the coastal and offshore engineering. The responses of piles under vertical-horizontal combined loading are separately analyzed and then superposed in current design practice. This simplified analysis approach does not take the coupling effect of the combined loads into consideration. The research on this topic is limited and the results reported to date are inconclusive with regard to the influence of vertical loads on the horizontal response of piles. In this paper, a series of centrifuge model tests under different vertical-horizontal combined loading conditions was performed to investigate the influence rules and mechanism of the combined loads on the response of piles in sand. The vertical load is shown to densify the soil near the pile and therefore decrease the horizontal displacement and bending moment of the pile: this is termed the “soil densification effect”. The vertical load induces an additional bending moment of the pile due to the lateral deformation of the pile: this is termed the “P-Δ effect”. The soil densification effect plays a dominant role in the early horizontal loading while the P-Δ effect is strengthened as the horizontal loads increases. These compound effect of these two seemingly opposing effects is a decrease in the bending moment of the pile decrease first then increase as the horizontal load increases. Additional settlement of the pile is caused by horizontal loading and isa positively correlated with the pre-vertical loads.

Modeling Single Piles Subjected to Evolving Soil Movement

AbstractTo design passive piles, it is critical to incorporate the impact of lateral soil movement (ws) and its profiles. This may be conveniently realized by using appropriate input parameters and a three-layer analytical model developed by the first author. In this paper, 25 (1-g) model tests were conducted on single piles in sand, subjected to a uniform (U), inverse triangular (T), or arc (A) profile of sand movement, to a final sliding depth (lm) of either 0.29l (l = pile embedment) or 0.57l, respectively. The measured response is subsequently simulated using the three-layer model to gain the input parameters and pile–soil interaction mechanism. The main conclusions (for lm = 0.29l) are as follows. First, the limiting resistance per unit length (at pile-tip level; pb) increases from uniform to inverse triangular and further to arc movement profiles at an increasing magnitude of ws. These profiles may be superimposed together to mimic evolving soil movement profiles. Second, the pb attains 30−60% of th...

A simplified method for the determination of vertically loaded pile-soil interface parameters in layered soil based on FLAC3D

The numerical analysis of pile-soil interaction commonly requires a lot of trial works to determine the interface parameters and the accuracy cannot be ensured normally. Considering this, this paper first conducts a sensitivity analysis to figure out the influence of interface parameters on the bearing behavior of a single pile in sand. Then, a simplified method for the determination of pile-soil interface parameters in layered soil is proposed based on the parameter studies. Finally, a filed loading test is used for the validation of the simplified method, and the calculated results agree well with the monitoring data. In general, the simplified method proposed in this paper works with higher accuracy and consumes less time compared with the traditional trial works, especially on the determinations of interfacial cohesive and interfacial friction angle.

Experimental Studies on Behavior of Single Pile under Combined Uplift and Lateral Loading

Abstract1-g model experiments were carried out in the laboratory to investigate the behavior of a single pile in sand under combined uplift and lateral load. Dimensions of the model pile were ascertained using physical scaling laws, based on adopted material properties of model and prototype pile foundations. The model pile is made up of aluminum and has outer and inner diameters of 25.4 and 19.0 mm, respectively. Different length-to-diameter ratios of 18, 28, and 38 are considered by varying the pile length to simulate behavior of both stiff and flexible piles. The test tank dimensions were chosen such that boundary effects are minimized. The size of the model steel tank is 1.0×1.0×1.2 m (depth). Experiments were performed on single piles embedded in sandy soil under independent uplift and lateral loading, and combined lateral and uplift loading. Results indicate that the load-deflection behavior is nonlinear for independent uplift and lateral load tests, as well as in the case of combined loading. It i...

Numerical study of the 3D failure envelope of a single pile in sand

The paper presents a comprehensive study of the failure envelope (or capacity diagram) of a single elastic pile in sand. The behavior of a pile subjected to different load combinations is simulated using a large number of finite element numerical calculations. The sand is modeled using a constitutive law based on hypoplasticity. In order to find the failure envelope in the three-dimensional space (i.e. horizontal force H, bending moment M and vertical force V), the radial displacement method and swipe tests are numerically performed. It is found that with increasing vertical load the horizontal bearing capacity of the pile decreases. Furthermore, the presence of bending moment on the pile head significantly influences the horizontal bearing capacity and the capacity diagram in the H–M plane manifests an inclined elliptical shape. An analytical equation providing good agreement with the 3D numerical results is finally proposed. The formula is useful for design purposes and the development of simplified modeling numerical strategies such as macro-element.

Numerical derivation of CPT-based p–y curves for piles in sand

The formulations for the lateral load–displacement (p–y) springs conventionally used for the analysis of laterally loaded piles have been based largely on the back-analysis of the performance of small-scale instrumented piles subjected to lateral load. Although such formulations have been employed with much success in industry, their applicability to large-diameter piles, such as those used to support offshore wind turbines, is uncertain and has necessitated further research in this area. Moreover, with the growth in popularity of in-situ cone penetration tests (CPTs), there are demands for a theoretically supported direct method that can enable the derivation of p–y curves from the CPT end resistance (qc). In this paper, a numerical derivation of CPT-based p–y curves applicable to both small- and large-diameter laterally loaded single piles in sand is presented. Three-dimensional finite-element analyses are performed using a non-linear elasto-plastic soil model to predict the response of single piles in sand subjected to lateral loads. The corresponding CPT qc profile is derived using the same soil constitutive model by way of the cavity expansion analogue. An extensive series of computations of the lateral pile response and CPT qc values is then employed to formulate a direct method of constructing p–y curves from CPT qc values. The proposed method is shown to be generally consistent with existing empirical correlations and to provide good predictions in relation to the measurements obtained during lateral load tests on instrumented piles in an independent case study.

Nonlinear analysis of laterally loaded single piles in sand using modified strain wedge model

This paper proposes a modified strain wedge model for the nonlinear analysis of laterally loaded single piles in sandy soils by using the Duncan–Chang model as well as the Mohr–Coulomb model to describe the stress–strain behavior of soils in the strain wedge. The input soil property for sandy soils only needs a relative density which can be easily estimated from in situ tests. The strain wedge depth is calculated by an iterative process and the subgrade reaction modulus below the strain wedge is assumed to increase linearly with depth, though it does not change with the lateral load applied to the pile. Seven case histories are used to verify the applicability of the proposed method. The results show the following: (1) good agreements are found between the predicted and the measured results of full scale tested piles; (2) the predicted deflections and moments using the Duncan–Chang model are almost the same as those using the Mohr–Coulomb model; and (3) the size effect of the pile diameter or width on the subgrade reaction modulus should be considered.

Modeling Laterally Loaded Single Piles Accounting for Nonlinear Soil-Pile Interactions

The nonlinear behavior of a laterally loaded monopile foundation is studied using the finite element method (FEM) to account for soil-pile interactions. Three-dimensional (3D) finite element modeling is a convenient and reliable approach to account for the continuity of the soil mass and the nonlinearity of the soil-pile interactions. Existing simple methods for predicting the deflection of laterally loaded single piles in sand and clay (e.g., beam on elastic foundation,p-ymethod, and SALLOP) are assessed using linear and nonlinear finite element analyses. The results indicate that for the specific case considered here thep-ymethod provides a reasonable accuracy, in spite of its simplicity, in predicting the lateral deflection of single piles. A simplified linear finite element (FE) analysis of piles, often used in the literature, is also investigated and the influence of accounting for the pile diameter in the simplified linear FE model is evaluated. It is shown that modeling the pile as a line with beam-column elements results in a reduced contribution of the surrounding soil to the lateral stiffness of the pile and an increase of up to 200% in the predicted maximum lateral displacement of the pile head.

Influence of Relative Pile-Soil Stiffness and Load Eccentricity on Single Pile Response in Sand Under Lateral Cyclic Loading

The environment prevalent in ocean necessitates the piles supporting offshore structures to be designed against lateral cyclic loading initiated by wave action, which induces deterioration in the strength and stiffness of the pile-soil system introducing progressive reduction in the bearing capacity associated with increased settlement of the pile foundation. A thorough and detailed review of literature indicates that significant works have already been carried out in the relevant field of investigation. It is a well established phenomenon that the variation of relative pile-soil stiffness (Krs) and load eccentricity (e/D) significantly affect the response of piles subjected to lateral static load. However, the influence of lateral cyclic load on axial response of single pile in sand, more specifically the effect of Krs and e/D on the cyclic behavior, is yet to be investigated. The present work has aimed to bridge up this gap. To carry out numerical analysis (boundary element method), the conventional elastic approach has been used as a guideline with relevant modifications. The model developed has been validated by comparing with available experimental (laboratory model and field tests) results, which indicate the accuracy of the solutions formulated. Thereafter, the methodology is applied successfully to selected parametric studies for understanding the magnitude and pattern of degradation of axial pile capacity induced due to lateral cyclic loading, as well as the influence of Krs and e/D on such degradation.

Nonlinear Response of Single Piles in Sand Subjected to Lateral Loads using khmax Approach

This paper presents results of analysis of full-scale pile load test data of 14 piles embedded in either loose or medium dense sands. The analysis was performed using two methods, p–y curve approach and a more recently developed khmax approach. Comparison of the results obtained using both the methods is also presented. A step-by-step analysis procedure is presented for predicting lateral load deflection response of single piles in sand using the khmax approach. The results presented show that the khmax approach has promise over the p–y curve approach because of its simplicity and the fact that it provides upper- and lower-bound curves, which are valuable guides to making engineering decisions. For loose sands, a new range of khmax values is recommended to better predict the lateral load–deflection response of single piles.

Lateral cyclic loading of single piles in sand

A number of tests have been carried out in the last few years at the LCPC centrifuge facility to study the behaviour of laterally loaded piles. This paper presents a centrifuge test programme of lateral cyclic loading of a single pile in sand. In these tests, the pile head fixity is free and the pile is eccentrically loaded since the point of load application is above soil surface (2.2 times the pile diameter). The experimental set up, the data acquisition and the processing techniques are described. Analyses are focused on the influence of cycles on the soil-pile interaction, on the pile head displacements, on the bending moments and on the P-y reaction curves.