Single Pile Research Articles

Experimental Study on the Failure Mechanism of Finned Pile Foundation under Horizontal Cyclic Loads

In order to study the failure mechanism of a finned pile foundation under horizontal cyclic loads, a physical model test of the pile–soil interaction of finned pile is designed in this paper. Based on the model tests, the pile top displacement, the cyclic stiffness of the pile foundation, and the response of pore water pressure within the soil around the pile were fully studied for the finned pile foundation under horizontal cyclic loads. It is found that the cyclic stiffness attenuation of the finned pile foundation is more severe than that of a regular single pile foundation, but the final stiffness at equilibrium is still greater than that of a regular single pile foundation. The accumulation of horizontal displacement at the pile top and pore water pressure within the soil around the pile mainly occurs in the first 1000 loading cycles, and an increase in fin plate size will reduce the magnitude of pore water pressure and pile top displacement. This study can not only deepen the understanding of the failure mechanism of finned pile foundation under horizontal cyclic loads, but also provide guidance for the design of the finned pile foundation.

Development of improved finite element formulations for pile group behavior analysis under cyclic loading

AbstractThe effect of cyclic loading is an essential factor leading to progressive soil strength degradation. Therefore, a comprehensive analysis of the pile‐soil system behavior under cyclic loading is required to ensure the stability of pile group. There is room for improvement in the inherent constraint of the conventional numerical model in terms of approximating the soil resistance distribution along the pile by point loads at element nodes, necessitating a specific element that integrates considerations of pile group effect and cyclic loading within a unified framework. This study aims to develop a newly specific type of element for efficiently predicting nonlinear behavior within the pile‐soil system, addressing simulations involving nonlinear pile‐soil interaction, pile group effect, and cyclic loading. Modified element formulations based on soil stiffness matrices and soil resistance vectors specifically address pile group effect and consider parameters that influence pile behavior under cyclic lateral loading. The numerical solution procedure with Newton‐Raphson iteration allows the calculation of pile responses in geometric and material nonlinear analyses. The validation of the proposed method includes several examples, comparing it with existing numerical solutions and experimental tests of single piles and pile groups under cyclic loading. These comparisons further support the consistency of the proposed method with measured data and validate its accuracy in considering group effect and cyclic loading. The parametric study illustrates the ability of the proposed method to capture cyclic loading parameters while considering the influence of the number and magnitude of load cycles, the cyclic load direction, and the installation methods.

Evaluasi Kapasitas Pondasi Tiang Pancang Menggunakan Data Kalendering Pada ABT1-ABT 2 Underpass STA 2+550 Binjai-Stabat

A pile foundation is needed to support the building, if the hard soil layer is very deep. The pile foundation functions to move or transfer the load above it (superstructure) to deeper soil layers. For this purpose, it is necessary to evaluate the capacity of a single pile and the capacity of a group of piles that are capable of carrying the load above them. Evaluation of pile capacity requires calendaring data in the form of field driving data which is carried out when the pile reaches hard ground with penetration and rebound values taken for 10 strokes. Based on calendaring data, single pole capacity analysis was carried out using several methods. The results of the bearing capacity analysis from one method are compared with other methods and their relationship with pile penetration. The capacity value of the pile group is calculated based on the pile efficiency. Most of the pile capacities show almost the same single pile capacity values, such as the Hiley method (666.16 kN), Navy-Mckay (752.14 kN), Janbu (440.91 kN), except that the Sanders method gives results that are much different from The value of other methods is 1138.28 kN, this could be because this method only considers the weight of the pile. The relationship between single pile capacity and pile penetration shows that the smaller the pile penetration value, the greater the pile capacity. This is obtained in all methods used, although with different calculation methods and method.

The Influence of Soil Reinforcement on the Performance of Single Pile and Pile Group Under Pullout Loads

The Influence of Soil Reinforcement on the Performance of Single Pile and Pile Group Under Pullout Loads

Soil-Pile Interaction of Laterally Loaded Fixed-Head Piles and Pile Groups in Unsaturated Sand

This study investigates the lateral behavior of piles in unsaturated cohesionless sandy soil using centrifuge modelling. The lateral loading was conducted on a single fixed-head pile and 2×2 fixed-head pile groups with 3D and 5D spacings. The results showed that the single fixed-head pile demonstrated greater magnitudes of lateral resistance response compared to the leading and trailing piles of the pile groups. Moreover, the piles experienced greater lateral loads when the water table was about a quarter of the embedded pile depth in the soil layer for the single fixed-head pile and leading piles in the group. The group efficiencies of the pile increased as the water table reduced up to half of the embedded pile length for the 3D pile spacing. However, this effect was negligible for 5D pile spacing. Considering the mixed unsaturated-saturated ground condition can lead to a more resilient foundation design under climate-induced and seasonal fluctuations of water table level and also pave the path for the inclusion of future climatic scenarios.

Analisis Daya Dukung Lateral Bored Pile Ø 80 Cm dengan Menggunakan Uji Beban Lateral dan Menggunakan Metode Elemen Hingga pada Proyek Menara BRI - Medan

Bored pile foundations are deep foundations that are often used in the construction of large construction sites located in dense areas with the consideration of reducing noise and the influence of vibrations that would occur if pile foundations were used. This analysis aims to calculate the lateral bearing capacity of the bored pile foundation based on the results of analytical calculations using the Broms method, the Davisson method, the Chin method, the Mazurkiewich method, and analyzing the displacement of the bored pile foundation based on loading tests in the field. and the results of soil modeling with Allpile and finite element methods with the Mohr-Coulomb soil model, and the Hardening Soil model. Based on the analysis that has been carried out, the ultimate bearing capacity of the bored pile based on SPT data using the Broms method is 18.92 tons, while the results of the interpretation of the loading test using the Davisson method are 18 tons, the Chin method is 18.98 tons, and the Mazurkiewich method is 19 tons. For the large deflection of a single bored pile with a load of 200% with the Allpile program the large deflection that occurs is 4.25 mm and analysis based on FEM PLAXIS 3D using soil modeling with Mohr - Coulomb large deflection of 3.0 mm and soil modeling with Hardening Soil 2.99 mm.

Lateral response and failure mechanism of single and group piles in cement-improved soil

Precast prestressed high-strength concrete (PHC) pipe pile with cement-improved soil is a novel pile foundation technique that has been extensively utilized in contemporary years due to the enhanced lateral load-bearing capacity in soft grounds. However, though several studies have shown the damage mechanism of single piles with cement-improved soil, the group behavior of such pile foundations is still largely unexplored. Hence, this article aims to illustrate the lateral capacity and tension-induced failure characteristics of single and 1 × 2 group PHC piles reinforced by cement-improved soil. Extensive 3D nonlinear finite element analyses have been performed and the precision of the numerical models is confirmed by a previous experimental-numerical study. The effects of pile spacing, embedment length, and cement-improved soil thickness were examined in terms of various lateral responses and damages. Results have revealed that the addition and thickening of CIS around core piles enhances the overall pile performance and protects the core pile from excessive tensile damage. Declines in head displacement and bending moment were found to be up to 45 % and 25 % for single piles, and up to 47 % and 24 % for group piles, respectively. Moreover, the presence of CIS makes the stress distribution mechanism between the trailing and leading piles in group arrangement more uniform. Results of this study are expected to provide valuable insights for a better understanding of the damage behavior of group precast piles reinforced with cement-improved soil.

Thermo‒mechanical behavior of energy pile group in dry sand subjected to a horizontal load

The energy pile is an innovative structure element designed to utilize geothermal energy while simultaneously supporting building loads by means of integrating heat exchange tubes into the pile foundation. Despite the intricate thermodynamic characteristics of energy pile groups, research on them remains limited. This study investigated the horizontal load transfer mechanism of an energy pile group in dry sand by conducting a model test on a 2 × 2 energy pile group subjected to horizontal loads. Specifically, the impact of heating or cooling a single pile within the energy pile group was examined. The results showed that the bending moment was significantly larger on a single pile subjected to a thermal load than that of the other piles, with the majority of this variation occurring in its upper part. Additionally, the horizontal load had a strong influence on the rotational angle and horizontal displacement of the energy pile group. The rotational angle and horizontal displacement decreased with increasing depth. With rising temperature, the interaction between the pile and the soil intensified, and the soil pressure on the upper part of the pile increased while that in the lower part decreased.

Lateral Response of a Single Pile in Unsaturated Sand

Lateral Response of a Single Pile in Unsaturated Sand

Effect of Horizontal Inclination of Lateral Load on Single Pile Behavior Subjected to Seismic Load

Effect of Horizontal Inclination of Lateral Load on Single Pile Behavior Subjected to Seismic Load

Calibrating resistance factors of pile groups based on individual pile proof load tests

Pile load tests have been utilized to reduce the uncertainty of pile resistance, thus leading to a higher resistance factor used in the Load and Resistance Factor Design (LRFD). Previous studies have primarily focused on calibrating resistance factors for single piles based on load tests. This calibration hinges upon the resistance bias factor of single piles, defined as the ratio of measured resistance to predicted resistance. Due to the redundancy in the pile group system, it is conventionally assumed that if the individual piles within the group achieve a lower reliability index (e.g., 2.0–2.5), the pile group as a whole attains the target reliability index of 3. However, the approach is empirical as it does not consider system redundancy directly. Moreover, this empirical approach disregards the correlation between resistance bias factors of individual piles, which is inherently influenced by the spatial variability of soils. In this study, the random finite difference method (RFDM) is employed to evaluate the correlation between resistance bias factors of individual piles in spatially variable soils. The resultant correlation matrix is subsequentially employed in Bayes’ theorem to update resistance bias factors using individual pile load test results and their corresponding test locations. The updated resistance bias factors are then used for the direct calibration of resistance factors for pile groups within the framework of LRFD. A pile group subject to vertical loading in undrained clays is adopted for illustration. Comparative analyses between the proposed approach and the empirical approach demonstrate that the latter tends to overestimate the resistance factor. Furthermore, the proposed approach enables the determination of optimal locations for conducting subsequent load tests based on previous test results.

Study on the structure parameters and design method optimization of blade-type screw steel pipe pile

The rationality of structure parameters of the blade-type screw steel pipe pile is the major factor in determining the safety, applicability, and economy of a pile foundation, but the existing design methods have not defined the specific approaches to calculating structure parameters of blades and steel pipes. To address this issue, an analysis of the strength theory was performed on spatial helical blades, revealing the ratio of blade width to steel pipe radius as the core index to do the structure parameters design of blade-type screw steel pipe pile and established a mathematical calculation model between the vertical bearing capacity of single pile and a. The rational value of a is 2.0–3.0 using numerical calculation. The correlation between blade thickness and wall thickness of steel pipes was determined using the force analysis based on the synergy between blades and steel pipes. Then the structure parameters design method of blade-type screw steel pipe pile with coordinated parameters was proposed. The rationality and superiority of this design method were verified by comparing the existing test data and the finite element simulative analysis. Based on this design method and the current specifications, such as the Technical Code for Building Pile Foundations, a safe, applicable, and economical optimization design method and flow of blade-type screw steel pipe piles were further proposed for engineering design reference.

Influence of the ribbed steel core on the inner interface mechanical behavior of the ESDCM pile

By virtue of the high strength, cost-efficiency and green construction, the expanded stiffened deep-cement-mixing (ESDCM) piles with steel cores own a great prospect to be applied for soft soil treatment in coastal and riverside regions. The dual-interface feature is a crucial factor affecting the bearing capacity of the ESDCM piles. However, the confining pressure characteristics of pile cores and the interface characteristics of steel pipe-soil-cement are unclear, limiting the practical application of ESDCM piles. Hence, in this work, we investigate the mechanical characteristics of the inner interface of ESDCM piles with steel cores via confining pressure transfer test and inner interface shear tests. The results demonstrate that the soil-cement column can withstand over 90 % of the confining pressure exerted on the outer interface, suggesting that the pile core may not be affected by confining pressure. Model piles with different steel cores have different interface failure modes, which can be described using either a three-segment or two-segment constitutive equation. Changing the inner interface structure has been proven to be a highly efficient pathway for enhancing the bearing capacity and adhesion conversion factor of the ESDCM pile. Compared with the smooth steel cores, the adhesion conversion factor can be reinforced up to 114.3 % by employing ribbed steel cores. Then, a model-pile bearing capacity calculation formula was established and verified for reliability. Moreover, the formula of a single pile based on inner interface shaft resistance was further proposed in combination with the actual operating conditions. This study highlights the mechanical characteristics of the inner interface of ESDCM piles, which guides engineering design and construction.

Thermal interference process between two energy piles in 2D model using transparent soil

Energy piles have the potential to contribute to the use of shallow geothermal energy. The heat exchange efficiency of energy piles in groups decreases compared with that of a single energy pile. Understanding the thermal interference mechanism between piles and its impact on the temperature response of the soil is crucial. In this study, the evolution processes of the temperature field of transparent soil around one and two energy piles in a 2D model were obtained by establishing the relationship between pixel intensity and soil temperature. This relationship was verified using a single energy pile test under heating conditions. Thermal images of transparent soil under different thermal loads (heating or cooling) were studied to investigate the phenomenon of thermal interference between two piles. The temperature superposition effect becomes more evident closer to the center of the two piles. Analyzing the temperature distribution in the soil and introducing a thermal interference coefficient revealed that the thermal accumulation effect between piles is more significant under lower thermal loads.

Kinematic response of floating single piles in saturated and nearly-saturated soil to P-waves

This paper presents closed-form expressions for the analysis of floating single piles subjected to vertically propagating harmonic P-waves. The foundation soil is treated as poroelastic medium, and can be either fully-saturated or nearly-saturated. We show that the existence of non-continuous air phase in the form of air bubbles dissolved in the pore water will have noteworthy effect on the vertical kinematic response of piles. Through parametric analyses we demonstrate that hydromechanical analysis techniques that consider soil as fully saturated may significantly over-estimate pile head displacements for frequencies relevant to seismic P-waves. In addition, we quantify differences in the response between end-bearing and floating piles, and show that these differences are more prominent when soil is not fully saturated. Although the proposed expressions have been derived while considering elastic soil and pile response, findings relevant to the effect of the degree of soil saturation to the vertical kinematic response of piles are generally applicable to any coupled stress-flow analysis method.

Experimental study of the effects of the void located at the pile tip on the load capacity of rock-socketed piles

To address the design challenge of the rock-socketed piles posed by the void located below the pile tip, the physical laboratory model tests were designed and performed to simulate rock socketed piles using similar materials. The study investigates the behavior of the single pile under axial loading with the void located at varying distances from the pile tip. Through multi-level load tests, the variations of unit pile side friction, pile tip resistance, pile axial force and pile settlement are obtained for different positions of the void from the pile tip, as well as after grouting. Its comparison to the rock-socketed pile without void is performed as a reference to quantify the reduction in its bearing capacity. The results are presented in the form of graphs for different void positions and its grouting shows the influence on pile bearing capacity and emphasizes the importance of its detailed cautious investigation and introduction in the analysis. The 2D finite element modeling of the model pile-the void based on ABAQUS is performed to further investigate the influence of the void below pile tip on the bearing capacity of model pile, applying the Mohr Coulomb model as the constitutive model of rock mass behavior. The critical distance of the void below the pile tip is determined.

The vertical loading tests of single and group piles by centrifuge modelling

ABSTRACT Pile foundations are widely used for tall buildings, but determining their capacity and behavior under load often involves expensive and lengthy field tests or imprecise numerical models. This research employed a centrifuge to perform vertical loading tests on single and grouped piles in dry sand, subjected to 100 times gravitational acceleration, to investigate pile capacity and load transfer mechanisms. The results from centrifuge modeling, numerical simulations, and field tests were consistent. The total pile capacity for a single pile was 5800 kN/m², while short and long pile groups had capacities of 6800 kN/m² and 9200 kN/m², respectively. End-bearing accounted for 40% of the capacity in single and short pile groups, and 13% in long pile groups. Surface friction was 95 kN/m² for single piles and 140 kN/m² for grouped piles. A method for estimating total pile capacity based on soil properties showed good agreement with empirical results.

Experimental Investigation of Vertical and Lateral Bearing Behaviors of Single Piles

Experimental Investigation of Vertical and Lateral Bearing Behaviors of Single Piles

Prediction of adjacent single pile deformation induced by tunnel excavation based on the Pasternak model

The construction of metro tunnels in soft ground would cause significant settlement of the ground surface and deformation of buildings and their foundations in the vicinity of the tunnels. The deformation laws of the pile of the neighbouring structures induced by the tunnel construction have not yet been fully identified. This paper analyzed the impact mechanism of tunnel construction on piles based on the Pasternak model, deduced the calculation methods of additional horizontal displacement and additional internal force of piles, and introduced three solution methods. The computational method results have been validated through numerical simulations using coupling of discrete element method and finite difference method and compared to select laboratory data. The results show that the model accuracy is better when the tunnel axis burial depth is less than the pile bottom burial depth. The analysis shows that the tunnel burial depth significantly influences the displacement distribution of the adjacent single pile, while the impact on the peak displacement is insignificant. The thickness of the elastic layer (C) is inversely related to the maximum horizontal displacement and internal force, but it does not impact the distribution patterns of the displacement and internal force. For thickness of the elastic layer (C), the bending moment’s point is constant at 2 m above and below the tunnel axis, whereas the shear force’s point remains constant at the buried tunnel axis’s depth and 4 m above the tunnel axis.

Critical liquefied soil thickness for response patterns of piles in inclined liquefied ground overlain by nonliquefied crust

AbstractLateral spreading has historically caused extensive pile failure in liquefaction‐prone areas during strong earthquakes. A critical design scenario involves piles embedded in lateral spreading ground composed of a nonliquefied soil crust overlying a liquefied layer; it is critical because both layers can exert loads on the piles. Different thicknesses of the liquefied soil and the upper nonliquefied crust may engender different pile response patterns. Accordingly, to investigate factors influencing the lateral responses of a single pile embedded in liquefied ground with a nonliquefied crust, we conduct parametric analyses. The effects of liquefied and nonliquefied soil thicknesses are analyzed first, followed by those of pile‐head rotational restraint, pile diameter, and lateral spreading displacement. We observe two main pile response patterns for various liquefied soil thicknesses. The ground can be categorized into thin or thick liquefied ground depending on whether its liquefied soil thickness is less or greater than a critical value, namely, critical liquefied soil thickness; this critical thickness is dependent on the pile‐head rotational restraint, pile diameter, and lateral spreading displacement. The difference in the patterns stems from the varying roles of the upper nonliquefied soil layer during lateral spreading. For the thin liquefied ground, the nonliquefied layer contributes to adding lateral spreading force; therefore, the displacement, moment, and shear force responses of the pile increase with the nonliquefied soil thickness. However, for the thick liquefied ground, the nonliquefied layer provides resistance to lateral spreading; therefore, the maximum displacement, moment, and shear force of the pile initially decreases and then gradually increases with the nonliquefied soil thickness.