Force Of Pile Research Articles

Study on bearing characteristics of single pile in heterogeneous layered foundation

Based on a project in Lanzhou City, Gansu Province, China, the bearing and internal force characteristics of 2 piles of different lengths under vertical load were tested and analyzed by using BOFDA technology and anchor pile method static load test. The results show that long pile has higher vertical bearing capacity and greater elastic working range, but the axial force of long pile and short pile has the same trend. The lateral friction resistance of the soil layer around the pile plays a role earlier than the pile tip resistance, and the lateral friction resistance of the upper soil layer plays a role earlier than the lower soil layer. The increasing amplitude of lateral friction resistance in different soil layers is also different. The settlement of short pile top is mostly caused by the displacement of pile bottom, and the pile tip resistance is more affected by the pile tip sediments. The relationship between pile end resistance and displacement under the influence of sediments can be analyzed by three-fold line model.

Thermo-Mechanical Coupling Load Transfer Method of Energy Pile Based on Hyperbolic Tangent Model

By employing the hyperbolic tangent model of load transfer (LT), this paper establishes the thermo-mechanical (TM) coupling load transfer analysis approach for an energy pile (EP). By incorporating the control condition of the unbalance force at the null point, the method for determining the null point considering the temperature effect is enhanced. The viability of the presented method is validated through the measured outcomes from model experiments of energy piles. A parametric investigation is conducted to explore the impact of the soil shear strength parameters, upper load, temperature variation, head stiffness, and radial expansion on the axial force, strain, and displacement of the energy pile under thermo-mechanical coupling. The results suggest that the locations of the null point and the maximum axial force are dependent on the constraint boundary conditions of the pile side and the two ends. When the stiffness of the pile top increases, axial stress and displacement increase, while strain decreases. An increase in the drained friction angle leads to an increase in axial stress under thermal-load coupling, but strain and displacement decline. The radial expansion has a negligible influence on the thermo-mechanical interaction between the pile and the soil.

Performance Analysis of Pile Group Installation in Saturated Clay

In offshore pile engineering, the installation of jacked piles generates compaction effects within soil, thus further affecting previously installed adjacent piles. This study proposes a three-dimensional numerical model for pile group installation, soil consolidation, and loading analysis. Subsequently, the effect of pile spacing and pile length-to-diameter ratio on the deformation, internal forces, and vertical bearing capacity of adjacent piles are investigated. The results indicate that with an increase in pile center distance, the peak lateral displacement of the adjacent piles decreases, whereas the peak vertical displacement increases. As the pile length-to-diameter ratio increases, the peak vertical and lateral displacements of the adjacent piles are enhanced. In addition, the peak axial force of the adjacent piles initially decreases and then increases with the penetration depth of the subsequent pile, whereas the peak bending moment initially increases and then decreases. The vertical bearing capacity of the subsequent pile is significantly superior to that of the adjacent piles. Therefore, the effects of pile installation on adjacent piles should be included in pile engineering. The impact of the subsequent pile installation on the bearing capacity of adjacent piles can be significantly reduced by increasing the pile center distance and pile length-to-diameter ratio. The findings provide useful guidance for pile group engineering.

Investigating the influence of an approach bridge on a pile-supported wharf at a liquefiable site under horizontal and vertical seismic excitations

The approach bridge of the pile-supported wharf is an important structure that connects the pile foundation platform and the land, and it has a significant impact on the safety of the high-pile wharf. However, the influence of an approach bridge on the seismic dynamic response of a pile-supported wharf has often been neglected in previous studies. Besides, the excess pore water pressure (Δu) generated under combined vertical and horizontal seismic components is typically greater than that induced by unidirectional excitations, which may further impact the dynamic response of pile-supported wharf. Firstly, this study developed a numerical method for simulating the approach bridge of a pile-supported wharf. Secondly, the three-dimensional finite element model of a pile-supported wharf with an approach bridge is established to investigate the dynamic response during horizontal and vertical seismic components. Additionally, the effects of seismic frequency and relative density of liquefied layer on the dynamic response of pile-supported wharf were also studied. By comparing with the experimental results, the numerical model effectively simulated the overall response of the pile-supported wharf and the liquefaction behavior of the surrounding soil. During high-frequency earthquakes, the influence of the approach bridge on the dynamic response of the pile-supported wharf is minimal, whereas it has a more significant impact during low-frequency earthquakes. Furthermore, vertical seismic components significantly amplify the effect of approach bridge on the lateral displacement and internal forces of piles. The effect of the approach bridge on the lateral displacement and internal force of the pile decreases with the increase of the relative density of the liquefaction layer.

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.

Finite Element Analysis of Combined Bearing Characteristics of Pile–Soil Interaction in Composite Foundation

Composite foundations have been widely used and promoted in practical engineering applications. However, research on the joint-bearing mechanism of piles and soil within composite foundations is still not comprehensive enough. This paper proposes a method for calculating the additional internal forces of piles and soil within composite foundations. Based on a three-dimensional finite element analysis, this study investigates the variation patterns of the stress, displacement, and additional internal forces of piles and soil in the depth direction under the action of upper loads when using friction piles and end-bearing piles. This research aims to reveal the bearing performance of piles and soil. The results showed that, under the same conditions and due to the presence of end-bearing effects, the internal forces experienced by the entire pile body of the end-bearing piles were more uniform, exhibiting significant advantages in resisting deformation and being able to withstand larger loads. Additionally, the diffusion mechanism of the vertical forces, stresses, and displacements of piles and soil is discussed. Due to the negative frictional resistance of soil and the influence of pile end-bearing effects, the distribution of internal forces and the displacements of piles and soil exhibited different characteristics. This study provides a scientific reference for the theoretical analysis and design of composite foundations.

Centrifuge modeling of end-bearing slender energy pile performance under temperature cycles

Slender energy pile shows a buckling deformation behavior under the coupling effect of temperature cycles and external loads, significantly affecting the long-term serviceability and even leading to the buckling failure. To investigate the thermo-mechanical performance of end-bearing slender energy piles under the long-term effect of temperature cycles, a centrifuge modeling experiment was conducted in this work, in which the temperature distribution, displacement, axial force, and bending moment of the energy pile during the long-term temperature cycle were measured. The results unveiled that the axial force of the end-bearing slender pile increases as temperature rises, potentially leading to a displacement neutral point in the lower part of the pile. Meanwhile, there was an embedding effect in the lower part of the slender pile, with a preliminary calculated embedment depth of 36.2 m. Temperature fluctuations can soften the soil at the pile end over time, diminishing the embedding effect on slender piles, and causing a reverse bending point to emerge at a depth of 45.5 m. The appearance of bending moments in the pile signaled the horizontal displacement encountered in the pile service life, warning the bearing capacity loss problem from changes in pile deflection.

Multi-Parameter Experimental Research on the Expansion Force Affecting Lime-Sand Piles under Preloading Pressure

Aiming at the problems that it is difficult to control the expansion force of lime-sand pile in the foundation correcting and how the upper existing structural pressure affects the expansion force of lime-sand pile, this paper adopts a new type of lime-sand pile reaction tester to carry out the experimental research on the expansion force of lime-sand pile under the influences of different pre-pressure, different mixing ratios, different heights, and different granular sizes. The purpose of this paper is to explore the influence of the pre-pressure brought by the existing building structure on the expansion force of the lime-sand pile and the coupling effect of the pre-pressure and other influencing factors on the expansion force of the lime-sand pile through the multi-parameter test. The results show that with the increase in pre-pressure, the expansion force of the lime-sand pile shows the trend of increasing first and then decreasing when the pre-pressure is 0.88 KN, the effect is most obvious and its expansion force can be increased by 14.9%. Within a certain range, the larger the proportion of quicklime is, the lower the expansion reaction force is. The expansion force of the lime-sand pile with the ratio of lime/sand/soil of 5:4:1 is the most ideal, and its value reaches 10.2 KN, which is 10% and 15.3% higher than the rest of the two groups, respectively. Within a certain range, the effect of specimen height change on the expansion force of the lime-sand pile is almost negligible. The smaller particle size of quicklime makes its reaction speed faster, the reaction degree is more full, and the expansion force is greater. The expansion force of the small particle size group was 12.1% and 34.2% higher than that of the medium and large particle size groups, respectively.

Influence of local scour on the dynamic response of bridges under barge collisions

The response assessment of bridges crossing navigable waterways under vessel collisions is commonly conducted assuming intact bridge models. However, local scour may occur at bridge foundations, which has been identified as one of the major hydraulic causes of bridge failures. Therefore, it is imperative to consider local scour in the design and analysis of bridges against vessel collisions. Many previous studies have focused on the bridge response under vessel collisions assuming deterministic scour depths with incremental values, without integrating a scour prediction modeling in the analysis. This work investigates the barge-bridge collisions in the presence of scour at pile foundations, by using empirical scour prediction models. The accuracy of each prediction model is evaluated using relevant laboratory test and field measurement records. Finite element (FE) models of a four-span continuous reinforced concrete (RC) bridge and a jumbo hopper barge are developed in LS-DYNA. The current study identifies the correlation between the upstream flow depth and the barge collision location in the analyses. Numerical results illustrate that both scour depth and collision location influence the displacement, shear force, and bending moment response of bridge piles. The struck bridge pier accommodates a considerably increased displacement with an increased scour depth, while the shear force and bending moment are primarily influenced by the collision location. The influence of scour on the barge-pier collision force is marginal. The maximum axial force in soil springs increases considerably with scour depth. The choice of scour prediction model shows a significant impact on the displacement, shear force, bending moment of piles, the displacement of struck pier, and the axial force of soil springs.

Magnification factor for pile internal forces of pile‐supported wharves under bi‐directional ground motions

AbstractIn order to determine the pile internal forces of wharf under simultaneous seismic excitation in orthogonal horizontal directions with ease, the total internal forces can be obtained by multiplying the pile forces of two‐dimensional model under transverse earthquake loading with a magnification factor. The factors were computed from the seismic response of wharves having various aspect ratios (length to width) and eccentricity ratios when subjected to 30 pairs of bi‐directional earthquake records. Mean magnification factors and their corresponding dispersion are presented for all ground motion ensembles. The influence of aspect ratio and eccentricity ratio is evaluated and discussed. It is concluded that the magnification factor can be expressed as the function of aspect ratio and eccentricity ratio, and follows lognormal distribution. The proposed equation of magnification factor can be an alternative for internal force analysis of wharves under bi‐directional ground motion.

Coupled SPH-FEM analysis of piled power transmission tower system subjected to debris flow

Debris flow is a type of highly dangerous geological hazard, which can pose significant threat to the safety of various infrastructures including power transmission tower system. However, the performance of piled power transmission tower system against debris flow has yet to be well investigated. A validated coupled SPH-FEM method was employed to investigate the behavior of a typical piled power transmission tower system subjected to various debris flows, accounting for influencing factors of slope angle, sliding distance, and density and thickness of debris flow. The findings revealed that the incorporation of power transmission tower was important to accurately estimate the impact force and horizontal displacement of the pile and the frontal piles undertook more than 70% of the total impact force; among the factors considered, the slope angle and density were found to be more influential. After examining the performance of existing prediction methods, two semi-empirical equations were proposed for respectively estimating the maximum impact force and horizontal displacement of pile based on multivariate regression analysis. Furthermore, it was found that debris flows did not likely cause steel tower to directly experience structural damages; however, its pile foundation could suffer moderate to severe damages depending on the debris flow conditions.

Stability Analysis of a Rocky Slope with a Weak Interbedded Layer under Rainfall Infiltration Conditions

Landslides not only cause great economic and human life losses but also seriously affect the safe operation of infrastructure such as highways. Rainfall is an important condition for inducing landslides, especially when a fault and weak interlayer exist on the slope, which can easily transform into a landslide and cause instability under the action of rainfall. To explore the effects of a soft interlayer, a fault, and extreme rainfall on slope stability, this paper takes the landslide on the right side of the G104 Jinglan Line in Shengzhou City, Shaoxing City, Zhejiang Province, China, as an example. The cause, failure mechanism, and characteristics of the landslide are analyzed through field investigation and borehole exploration in the landslide area. The slope is simulated by numerical analysis, and the stability of the landslide under natural conditions and extreme rainstorm conditions is calculated using the strength reduction method. The stability of the slope before and after treatment is compared, and the effectiveness of the treatment measures is verified by combining the field monitoring data. At the same time, the complex geological structure and rainfall are considered to have been the main factors leading to the G104 landslide. Near the fault, the weak interlayer of the landslide was easily disturbed, the deformation trend of the deep displacement was consistent with rainfall, and the axial force of the anti-slide piles at the weak interlayer was correspondingly large. For a wedge rock slope, “excavation unloading” and “prestressed anchor + prestressed anchor cable + anti-slide pile” are effective treatments. This paper reveals the effects of a weak interlayer, a fault, and strong rainfall on a rocky high slope, providing predictions of instability modes and time evolution patterns for similar complex geological slopes under rainfall infiltration conditions and providing references for their treatment measures.

A method for assessing non-uniformity of thermally induced stresses in the cross-section of energy piles

The non-uniform distribution of thermally induced stresses within energy piles presents a significant challenge when assessing their thermo-mechanical behavior. This study proposes an innovative approach to assess the non-uniformity of thermally induced stresses in energy piles by employing a novel parameter known as the concentration coefficient of thermally induced stress (Kth). Kth serves a dual role: firstly, it quantifies the non-uniformity of thermally induced stresses in the cross-section of energy piles, and secondly, it enhances the accuracy of determining the average thermally induced stress and axial force in energy piles when combined with field testing. Sensitivity analyses were performed using both the Taguchi method and the full factorial test method to investigate the influence of various factors on Kth. The descending order of impact weights for each influencing factor on the non-uniformity of thermally induced stress is as follows: pile-soil stiffness ratio, pile configuration, soil's Poisson's ratio, soil-pile thermal expansion coefficient ratio and slenderness ratio, with pile-soil stiffness ratio, pile configuration and soil Poisson's ratio combined effects take up over 90% of the observed variations in Kth. Notably, when the soil stiffness is low, Kth can exceed a value of thirteen, indicating an extreme non-uniformity in the thermally induced stress distribution across the cross-section. Additionally, a lower number of heat exchanger pipes is associated with a more non-uniform thermally induced stress distribution, but the non-uniformity tends to stabilize as the number of U-shaped heat exchanger pipes exceeds three.

Study on the dynamic construction mechanics of side piles in metro station using the pile-beam-arch method

Based on the Tianhe East Station in Guangzhou Metro Line 11 engineering, this paper analyzes the formation mechanism of soil arching effect (SAE) of station by pile-beam-arch (PBA) method in the excavation process and studies the mechanics and deformation laws of side piles in different construction stages under different pile spacing conditions. The results show that the formation, development and destruction of SAE between piles are closely related to construction process. Both too large and too small pile spacings are not conducive to the development about SAE between piles; when it is located between them, the SAE between piles exerts greatly. In the form of composite lining system, supporting piles as well as SAE between piles play an effective role in supporting soil behind piles. The lateral deformation of pile body is most significant in the completion of buckle arch to the excavation of first soil layer, which is the critical construction phase to reduce lateral deformation of side pile. The axial forces of side pile increase gradually with the excavation of station, and the change is the most drastic at the excavation for first soil layer. The influence of pile spacing on vertical settlement and axial force of side piles is much greater than that of horizontal displacement and bending moment.

Bidirectional static loading tests on barrette piles. A case history from Ho Chi Minh City, Vietnam

Bidirectional static loading tests were conducted on two strain-gage instrumented barrettes installed to 72 m depth in Ho Chi Minh City, Vietnam. The barrettes were to support a 16-storey building with 5 basements. The soil profile comprised layers of medium coarse to fine sand, medium clay, firm to stiff clayey soil, and dense sandy silt. The region is experiencing an ongoing land subsidence affecting the upper about 40 m of soil and, on average in the city, the ground surface is currently settling 16 mm/year. The test records were processed by means of effective stress analysis to provide the axial pile force distribution, load transfer functions, and equivalent head-down load–movement curve. The analysis was then used to obtain the equivalent pile-head load–movement response adjusted to the planned 22 m deep basement excavation. Load transfer functions were back-calculated from the test records and indicate that the construction will show somewhat large load-transfer movement. However, because the equilibrium plane will be below the subsiding layers, below 40 m depth, downdrag is not expected to affect the building. The load response of the barrettes is compared to the results of a bidirectional (BD) loading test on a 1.8 m diameter bored pile at an adjacent project.

Mechanical Difference Analysis of Single-row and Double-row Side Piles in Stations by PBA Method Based on Model Test

This study employs the pile-beam-arch (PBA) method to investigate the force-evolution law of micro-steel pipe piles during the excavation process, focusing on a Guangzhou metro-station project. Through laboratory model tests, we compared and analyzed the mechanical evolution laws of single-row and double-row side piles. Our findings revealed a significant soil arch effect in both single-row and double-row piles; with similar distribution patterns and peak-stress range. As soil excavation progresses, the soil arching effect shifts downward. Notably, the stress concentration in double-row piles is weaker than that in single-row piles, especially in the soil range of 0–50 mm after the piles. This is attributed to the looser soil between single-row piles, resulting in more evident stress release. The attenuation amplitude of the Y-direction stress of the double-row piles was considerably smaller than that of the single-row piles. The soil arching between the back-row piles in doublerow configurations exhibits shielding effects on the force of front-row piles, significantly weakening the soil pressure on them. This impact alters the force of the front-row piles, even causing the tip of the front-row piles to bend in reverse. The research results provide important insights for similar projects and can serve as a valuable reference.

Dynamic centrifuge model tests on piled raft foundation and evaluation of sectional forces of piles

Dynamic centrifuge model tests on piled raft foundation and evaluation of sectional forces of piles

Research on Load Bearing and Deformation Behavior of “Pile–Wall” Retaining Structure

The “pile–wall” structure, which considers conventional temporary retaining piles as parts of the underground structure in the normal working stage, has been practiced, but there are insufficient studies on the optimization of the design of the “pile–wall” structure and the influence of various factors on the structural stresses and deformations. In order to analyze the factors affecting the stresses and deformations of the “pile–wall” structure, the numerical simulation of the “pile–wall” structure was carried out with the help of finite element simulation software Plaxis 3D through the excavation of Wuhan Optics Valley Center City Distributed Energy Project. The research of stresses and displacements on the “pile–wall” structural under the influence of different factors were carried out. The results show that the number of pile–wall connection nodes, the pile–wall thickness ratio, and the pile–wall stiffness ratio have influences on the stresses and deformations of the “pile–wall” structure. The number of connection nodes which is 4, the pile–wall thickness ratio which is 1 : 0.3, and the pile–wall stiffness ratio which is 1 : 1 are the most reasonable for the deformation and force of pile–wall structure in the project. The research results have good reference and guiding significance for the actual “pile–wall” excavation engineering structure, and the purpose of energy‐saving and consumption‐reducing construction can be achieved by seeking the reasonable values of the three and optimizing the construction program.

Assessment of the impact of a high-rise building on the stress-strain state of the foundation and structures of existing buildings in dense development

One of the most progressive problems of modern urban planning is the gradual decrease in areas suitable for construction, especially within the historical districts of cities. This prompts developers to increasingly develop sites in difficult engineering and geological conditions, which are often located within dense buildings.
 Today, the construction of multifunctional residential complexes combines the construction of high-rise residential sections and commercial real estate buildings with multi-level parking lots, which are often located in close proximity to each other. Often, the sequence of construction of these buildings is stretched over years or even decades, for example, due to an unfavorable economic climate or the instability of the political situation in the country, which leads to the commissioning of only certain stages of construction. The subsequent resumption of construction work requires taking into account the mutual impact of new construction and observations of previously constructed buildings during the construction of new structures.
 The execution of deep pits at the stage of laying the foundations of new buildings, as well as the substantial weight of high-rise buildings, causes a change in the stress-strain state of the adjacent soil massif, so designers face the task of determining the impact of such construction on the adjacent buildings.
 This article presents the results of a study of the change in the stress-strain state of load-bearing structures and foundations an existing building, taking into account the mutual impact of an adjacent high-rise section of a residential complex.
 The calculations were performed in two independent software systems Plaxis 3D and LIRA-FEM, in the spatial formulation of tasks, for a comprehensive assessment of the SSS of the system "soil base-foundation-superstructure".
 The zone of impact of new construction on the adjacent buildings, the values and character of additional displacements of foundations of adjacent structures are determined. The regularities of changes in the calculated forces in piles are shown, which indicate a decrease in axial forces in piles up to two times at the interface with the foundations of the new building and an increase in the load on the piles of the central zone by up to 17%. The obtained results show a tendency to redistribute stresses in the foundation slab from the bearing zones to the span zones, as well as in the bearing vertical structures of the lower floor of the existing building.

Calculation and Application of Ultimate Lateral Friction Resistance of Concrete Piles under Different Soil Layer Materials

In practical engineering applications, it usually gets the expected value of the ultimate side friction of concrete piles by the empirical parameter method. The expected value of the ultimate side friction of concrete piles cannot achieve maximum optimization due to the complexity of formation conditions and the lack of experience of technicians. To accurately obtain the ultimate lateral friction resistance of piles in homogeneous soil layers, optimize the standard value of pile ultimate lateral resistance, ensure construction safety, and save construction costs, the research method combining theoretical derivation and on-site measurement data validation was done in the manuscript. Based on the shear strength of the pile-soil interface of different materials and the shear performance of the soil around the pile, a calculation equation for the standard value of the ultimate lateral friction resistance of concrete piles in different homogeneous soil materials was derived and applied to the equation for calculating the ultimate bearing capacity of foundation pile and the axial force of pile. Finally, based on an engineering example, the calculated results were compared with the measured resultsThe research results show that in thick coarse-grained soil, as the foundation pile is short, the ultimate bearing capacity of a single pile obtained using the calculation equation deduced in this paper is less than that obtained using the empirical equation provided by the national code. In a deep cohesionless homogeneous soil material, the concrete pile shaft axial force calculation using the pile shaft axial force calculation equation deduced in this paper is close to the measured value when the foundation pile bears the ultimate load; the proposed new method has good application value.