Open-ended Piles Research Articles

Novel Explicit Models for Assessing the Frictional Resistance of Pipe Piles Subjected to Seismic Effects

This paper introduces novel explicit models to predict the frictional resistance of open and closed-ended pipe piles subjected to seismic loading. This research employs genetic programming (GP) and multiobjective genetic algorithm-based evolutionary polynomial regression (EPR-MOGA) to develop closed-form expressions for estimating pile frictional resistance, utilizing widely used input parameters for enhanced practicality and applicability in engineering practice. The proposed models are developed using only three input variables: the corrected standard penetration test (SPT) blow count (N1)60, the pile slenderness ratio (L/D), and the peak ground acceleration (PGA). This deliberate reduction in input complexity significantly enhances the models' applicability across a wide range of geotechnical scenarios and industries. The accuracy of the developed models was assessed via the coefficient of determination (R2), root mean squared error (RMSE), and mean absolute error (MAE). In the case of the GP model, the evaluation metrics for the testing set for open-ended piles (R2, RMSE, and MAE values) are 0.89, 0.43, and 0.35, respectively, whereas the corresponding values for closed-ended piles are 0.93, 0.38, and 0.3, respectively. On the other hand, the EPR-MOGA approach achieves similarly encouraging results, with performance metrics of 0.92, 0.37, and 0.29 for open-ended piles and 0.91, 0.39, and 0.30 for closed-ended piles.

Stress State Analysis of the Soil Plug of Open-Ended Piles during Impact Driving Using Particle Flow Code (PFC)

Stress State Analysis of the Soil Plug of Open-Ended Piles during Impact Driving Using Particle Flow Code (PFC)

Installation of open-ended piles: A numerical investigation into the effects on the state of silica sand

Up to this day, there are great uncertainties in the design procedures of monopiles, especially concerning the soil state condition and penetration response during their installation. A numerical model, based on the Coupled Eulerian method and using the hypoplastic law with intergranular strain, is proposed and validated in this paper, after which a series of open-ended pile installation tests have been carried out numerically, to investigate the influence of the jacked installation on the initial conditions for three types of silica sand. A range of soil densities and pile diameters is considered in this analysis. A full investigation of the installation forces, stress level, changes in volume-stress level and voids ratio is conducted. The numerical solution provided a correlation between the penetration resistance and the granulometric properties of the studied sands. Subsequently, the radial stresses in the surrounding soil mass are correlated with the type of sand and its relative density. The stress-volume state of a set of points in the soil domain during installation is presented and discussed from the critical state framework, revealing the contribution of the in-situ state in the pile installation. Finally, the lateral earth pressure resulting after installation is presented.

Numerical modeling of open-ended piles

Deep foundations are generally used when significant loads are applied, and the site conditions do not allow for the implementation of soil reinforcement processes. This research focuses on studying the behavior of piles in a frictional environment, used as foundations for offshore structures in dense sands, involving anchor depths and overloads significantly higher than those encountered in onshore applications. The bearing capacity of open-ended driven piles plays a crucial role in this study. Therefore, a series of tests were conducted in the literature on model piles in a calibration chamber, which is considered a tool for physical modeling, allowing for significant penetration of instrumented model piles under confinement conditions similar to those experienced by real piles. Emphasis is placed on predicting the ultimate load capacity of open-ended piles using numerical methods. Calculations were performed using the finite element code PLAXIS to numerically reproduce the same shear stresses as those measured on the model during various phases of the experiment. The approach aims to validate the documented experiments in the literature and compare the ultimate load capacity of an open-ended pile to that of a closed-ended pile. Our study is limited to the case of a single pile, subject to static and axial force. The results show that it is possible to achieve a good agreement between the experiment and the numerical modeling with a relatively simple model, provided that the soil parameters are chosen correctly and the interface stiffness is adequately simulated.

A CPT-Based Design Framework for Uplifted Open-Ended Piles Installed in Spatially Variable Sandy Soils. I: Soil Resistance Design Line Optimization

A CPT-Based Design Framework for Uplifted Open-Ended Piles Installed in Spatially Variable Sandy Soils. I: Soil Resistance Design Line Optimization

A CPT-Based Design Framework for Uplifted Open-Ended Piles Installed in Spatially Variable Sandy Soils. II: Implications to Site Investigation and Pile Design for Offshore Wind Farms

A CPT-Based Design Framework for Uplifted Open-Ended Piles Installed in Spatially Variable Sandy Soils. II: Implications to Site Investigation and Pile Design for Offshore Wind Farms

Experimental and Numerical Flexural–Torsional Performance of Thin-Walled Open-Ended Steel Vertical Pile Foundations Subjected to Lateral Loads

This research investigates the effects of torsional moments on the mechanical behavior of thin-walled open-ended vertical pile foundations subjected to lateral wind loads. The aim of this research is to determine and quantify the errors using traditional design methods and provide more effective alternatives. The warping and torsion effect generated over the piles due to the resultant lateral load impact outside the shear center is analyzed in field tests. Complementarily, a two-dimensional finite element model based on the simple bending stress–strain state, as well as a three-dimensional finite element model considering torsional effects, were implemented and their results analyzed. Finally, a comparative analysis between the in-field lateral loading tests and the finite element model approaches was established by comparing load–displacement curves and using a non-linear Wrinkle model of the soil. Additionally, correlations between the experimental and finite element model errors for the cross-sections pile with a different torsional constant and torsional susceptibility index are shown. From the results, it has been ascertained that the slender thin-walled open-ended pile foundations are particularly sensitive to small load deviations from their center of gravity; this leads to the fact that the slenderer the load and the greater its eccentricity, the more it affects the torsion and warping of the pile. Calculation methodologies usually consider a simple in-plane bending behavior, which leads to errors between 44 and 58% in comparison with the experimental results obtained.

DEM study of particle scale effect on plain and rotary jacked pile behaviour in granular materials

The capacity of open-ended piles strongly depends on the potential plugging occurring during installation. The Discrete Element Method (DEM) is particularly suitable to the study of pile plugging, as it can model large soil deformation. However, DEM simulation of the 3D boundary value problems is computationally expensive, and particle upscaling is usually used to reduce the number of particles modelled. In this paper, two granular beds were created with the same average porosity, initial stress field and contact parameters, but different particle scales. Two pile geometries were installed by plain and rotary jacking. Normalised results show that the pile penetration mechanism is strongly affected by the particle scale. Larger particles lead to earlier pile plugging, higher shaft resistance and require a greater force to penetrate the ground. This effect can be linked to a modified penetration mechanism, with larger shear zones and less well defined “nose cone” under the pile tip for larger particles. Changing particle scaling has a neutral effect on the total penetration resistance of a rotary jacked pile, but reduces the base penetration and increases the plug resistance. Maximising the ratio of particle scale to wall thickness is key to adequately capturing the pile coring mechanism.

Estimating initiation conditions for extrusion buckling of driven open-ended piles

The potential for pile tip damage and extrusion buckling has become an increasing concern for the offshore wind industry following the trend toward the use of large-diameter thin-walled pile foundations, either as monopiles or as part of a jacket structure. Extrusion buckling may be triggered by an initial pile tip fabrication imperfection or pile damage during transport and handling. It may also be triggered during driving through strong heterogeneous sediments. Numerical analysis of the problem requires advanced and computationally expensive techniques because of the three-dimensional, dynamic and large-deformation nature of the pile and soil deformations. The problem is addressed here by combining coupled Eulerian–Lagrangian simulations with geotechnical centrifuge model test data in dry dense sand. Both approaches consider pre-dented piles with the objective of estimating the soil strength, characterised by the cone resistance, at which minor initial damage will start to propagate. Simplified analysis of structural dent propagation and radial stresses generated in the soil during advance of a deformed pile led to a simple calculation procedure to assess the potential for extrusion buckling. Reasonably good agreement was achieved between the proposed calculation method, numerical simulations and centrifuge tests data, rendering the approach a valuable screening tool for practical application.

Data-driven modeling of ultimate load capacity of closed- and open-ended piles using machine learning

ABSTRACT Field pile load tests are fairly expensive experiments that can be applied to certain pile types required to be installed in full scale. Hence, it is neither practical nor efficient to perform a load test for every installed pile. While there exist many empirical relations for predicting pile capacities, such methods typically suffer from accuracy and generality. Therefore, current geotechnical practice still looks for methods to accommodate full-scale pile load testing to serve as accurate and practical tools. In this study, load bearing capacities of closed- and open-ended piles in cohesive and cohesionless soils are predicted using machine learning. Nine such methods are utilized in the analyses where Cone Penetration Test (CPT) and pile data are considered as the learning features necessary to teach those methods the database gathered via a comprehensive search. Then, machine learning models are developed, and the databases are separated into five-folds according to the cross-validation-principle, which are used for both training and testing of the machine learning methods. Model predictions are validated with classical CPT-based equations. Results indicate that Relevance Vector Regression and the Random Forest methods typically generate considerably better predictions than the other methods and empirical equations. Thus, machine learning methods are found as reliable tools to predict the pile load capacities of both open-ended and closed-ended pile provided that there is a large enough database and that an appropriate method is used.

Analytical solutions of soil plug behaviors in open-ended pile driven by impact load

Analytical solutions of soil plug behaviors in open-ended pile driven by impact load

Experimental study on penetration characteristics of an open-ended pile under static and dynamic driving methods

Open-ended piles have been widely adopted in both offshore and onshore geotechnical engineering projects. However, the influence mechanism of pile driving methods on the penetration characteristics of the open-ended piles is not clear. Therefore, this paper presents simulations of an open-ended pile penetrating through a silt layer to a fine sand bearing stratum using static and dynamic driving methods respectively in a series of indoor model tests. Properties including pile sinking resistance, pile end resistance, pile side friction resistance, pile load transfer law and soil plug formation during penetration are analyzed. The results show that the PLR value of the hammered pile is always greater than that of the static pressure pile in the stable sinking stage, while the IFR value of the latter in the sand layer is significantly higher than that of the former. The resistance of the hammered pile under the same penetration depth is less than that of the static pressure pile and increases sharply when entering the holding layer. In addition, the final pile driving resistance of the hammering method is 66.68% of the static pressure pile driving resistance, and the pile end resistance from the static pressure method and hammering method account for 75.4% and 77.6% of the total resistance respectively In the choice of construction method, the static pressure method is more suitable for silty soil, and the hammering method can show its advantages in fine sand formation.

Efficacy of Design Methods for Predicting the Capacity of Large-Diameter Open-Ended Piles

Large-diameter open-ended piles (LDOEPs) are increasingly being used for support of infrastructure projects. Yet, many of the methods in current use for predicting their capacity are based on studies involving small-diameter piles. The efficacy of eight commonly used pile design methods was explored using a database of 64 load tests on full-scale LDOEPs. Capacities were computed using eight commonly used design methods based on both the standard penetration test (SPT) and cone penetration test (CPT). The calculated capacities were compared with capacities interpreted from load tests using several failure interpretation criteria. The study demonstrated that cone penetration test (CPT)-based methods are somewhat superior to SPT methods, but all methods exhibited scatter between measured and predicted capacities, with the computed capacity off by a factor of two in many load tests. Several plugging conditions were compared for each of these methods. Seven of the eight design methods better predicted pile capacity considering that the piles are unplugged, ignoring contributions of the soil internal friction on the pile inner diameter. These findings suggest that (1) LDOEPs do not plug during static loading, with little contribution of interior skin friction to pile capacity; and (2) LDOEPs do not develop significant end bearing.

Soil Plugging Effect of Jacked Open-Ended Pile in Layered Foundation

Soil Plugging Effect of Jacked Open-Ended Pile in Layered Foundation

Experimental investigation of bearing mechanism of closed- and open-ended piles supported by thin bearing layer using X-ray micro CT

In order to clarify the bearing mechanism of closed-ended and open-ended piles supported by a thin bearing layer, pile-loading tests are conducted on model grounds with different bearing layer thicknesses, and the soil deformation characteristics around the pile tips are observed by X-ray micro CT. In the case of open-ended piles supported by a thin bearing layer, the soil in the pile greatly displaces following the downward displacement of the soil located more deeply than the pile tip, and the soil density in the pile becomes lower than when the bearing layer thickness is sufficiently large. These characteristics probably cause lower inner friction and lower base resistance, resulting in a lower bearing capacity. When the bearing layer thickness is more than three times the pile diameter, the bearing capacity is much higher than when the bearing layer thickness is the same as the pile diameter. In addition, soil deformation which occurs is almost entirely in the bearing layer, and the changes in bearing capacity are hardly affected by the soft layer below the bearing layer. The experimental findings obtained in the present study support the idea that the criterion for the bearing layer thickness, where the influence of a thin bearing layer on the bearing capacity can be ignored, is three times the pile diameter, regardless of whether the pile tip is open or closed.

Durable life assessment of centrifugal stratified PHC piles in marine environment

This study proposes an analytical approach to assess the durable life of pre-stressed high-strength concrete (PHC) pipe piles exposed to the marine environment with consideration of centrifugal stratification and different end types. The durable life of the PHC pile is divided into two stages: the initiation stage for chloride penetration and the propagation stage for rust accumulation. To simulate the two stages, a two-layer composite cylinder diffusion model and a thick-walled ring mechanical model are developed based on the governing mechanisms. The proposed diffusion model is verified via comparisons with the numerical models with respect to chloride concentration under different stages. Then, extensive parametric studies based on the proposed method are performed to investigate the effects of end type, cover thickness, and steel bar diameter on the durable life of a PHC pipe pile. The results indicate that both increasing the cover thickness and using the closed-ended pile can significantly extend the durable life of a PHC pipe pile. Furthermore, the open-ended pile with a thinner mortar layer has a longer durable life, while the durable life of a closed-ended pile only slightly increases with a larger thickness of the mortar layer.

Hydro-Mechanically Coupled Numerical Modelling on Vibratory Open-Ended Pile Driving in Saturated Sand

Vibratory pile diving with resonance-free technique is an advanced construction approach that can play an important part in underground engineering. This paper aims to propose a numerical model for this construction approach, which commonly involves soils below the groundwater table. Such simulations are still challenging tasks as dynamic analyses considering hydro-mechanical interactions are very complicated. Several simulations have been performed by constructing a user-defined element in the finite element code ABAQUS or developing an inhouse finite-element program for this issue. These simulations have some limitations and pay less attention to open-ended piles. This paper presents a way to simulate the vibratory open-ended pile driving in saturated sand using the finite difference code FLAC3D. The model computation efficiency is increased around 67 times by the density scaling method and this method has little effect on the numerical stability. The proposed model can generally replicate the pore pressure results of a model test. The maximum excess pore pressures are predicted with a percent error of 2–22%, and these maximums occur near the pile toe. The excess pore pressure of an observation point slowly decreases after the pile toe passes the point. This work could provide an efficient and effective method for simulating vibratory open-ended pile driving in saturated sand.

Friction capacity of open-ended piles driven into sand

Friction capacity of open-ended piles driven into sand

Investigation of soil plug formation in hollow piles using PIV technique

ABSTRACT The foundation systems for bridges and marine structures demand deep foundations like hollow driven open-ended piles, where hard-bearing strata exist on deep soil underneath loose inland and oceanic sea floors. During this driving process, a soil plug is formed near the hollow pile tip region, resulting in soil crushing and compression at the pile tip. The conventional methods fail to predict such volume changes and densification of the embedded soil. The present study utilised Particle Image Velocimetry (PIV) technique to assess the plugging at the pile tip and compare the penetration rate under different infill densities. The PIV results indicated that at a specific energy, pile geometric parameters and infill conditions strongly influenced pile drivability in a granular medium. Due to disturbance caused by pile driving at the base, high compressive strains are observed for large diameter piles, while large dilative strains developed soil plug during the penetration stage for small diameter piles. The plug surface profile was concave for larger diameter piles due to active arching mechanism, while it was convex for small diameter piles due to passive arching generated by lateral soil confinement within the pile wall surface.

Three-Dimensional Modelling of Non-Linear Wave-Induced Seabed Response around Offshore Open-Ended Pile

This paper analyses the fluid–seabed–structure interactions (FSSI) around the open-ended pile by applying the in-house solver established on the open-source Computational Fluid Dynamics (CFD) platform. The Reynolds-averaged Navier–Stokes (RANS) equations are solved to simulate the hydrodynamic interactions between waves and open-ended piles. Biot’s poro-elastic theory (quasi-static model) is used to reproduce the wave-induced seabed responses. The parameter analysis indicates that the wave period, degree of saturation of seabed and pile diameter have a great influence on the development of the transient seabed liquefaction depth around the pile. In addition, the distribution of the pore water pressure vs soil depth in the inner zone of the pile presents a “V” shape rotated 90 degrees counterclockwise.