Model Piles Research Articles

Study on the Effect of Heat Transfer Characteristics of Energy Piles

The thermal performance of energy piles equipped with new metal fins to improve heat transmission is examined in this research. The solid heat transfer module of COMSOL Multiphysics was used to create a 2D numerical model of the energy pile, utilizing the energy pile at a field test site in Nanjing as an example. By contrasting the experimental data, the COMSOL Multiphysics model’s correctness was confirmed. After that, a new kind of energy pile fin was created to improve the heat transfer of the pile. The impact of the new fin type on the energy pile’s heat transfer efficiency was assessed, and the temperature change within the soil surrounding the pile before and after the fin was set was examined by contrasting the parameters of pipe configuration, buried pipe depth, and concrete thermal conductivity. The results indicate that after setting the fins to run for 336 h, the temperature of the concrete area increases by 10.8% to 12.3%, and the temperature of the region surrounding the pile increases by 5.3% to 8.7% when the tube diameter is chosen to be between 20 and 40 mm; The fins maximize the heat transfer temperature between the surrounding soil and the concrete, and as the tube diameter increases, the temperature drops. For 336 h of pile operation, the temperature of the concrete may be raised by 10.8% to 12.3% after the fins are set, and the temperature around the pile can be raised by 5.3% to 8.7%. The heat transmission efficiency of the energy pile can be improved by raising the temperature of the soil surrounding the pile through an increase in the concrete’s thermal conductivity; however, the degree of improvement diminishes as the conductivity rises. It is intended that this study will offer insightful information on the best way to design energy pile heat transfer efficiency.

A New Method for Predicting Dynamic Pile Head Stiffness Considering Pile–Soil Relative Stiffness Under Long-Term Cyclic Loading Conditions

Under long-term horizontal cyclic loading, the evolution characteristics of the loading and unloading stiffness of piles are an important representation of pile–soil interaction. However, research in this area is limited, particularly regarding the impact of factors like pile–soil relative stiffness. In this study, laboratory tests with a long-term horizontal cyclic loading strategy were conducted to study various factors, including different cyclic amplitude ratios (ζb), cyclic load ratios (ζc), and pile–soil relative stiffness (T/L) in sandy soil, on dynamic pile head stiffness. The results show that the normalized cumulative displacement increases with the number of cycles and the ratio of T/L but tends to decrease as ζc increases. As ζb increases, the normalized cyclic loading stiffness also rises, while it has little effect on the normalized cyclic unloading stiffness. On the other hand, as ζc or T/L increases, the cyclic loading stiffness increases while the unloading stiffness decreases. Based on these observations, prediction formulas for normalized cumulative displacement and cyclic loading and unloading stiffness were established and confirmed with test results. The findings of this study provide methodological references for establishing models of pile–soil interaction under cyclic loading and for predicting loading and unloading stiffness under different influencing factors.

Study on the Ratio and Model Test of Similar Materials of Heavily Weathered Granite.

To study the bearing characteristics of rock-socketed single piles on the southeast coast of Fujian Province, we conducted similar material ratio tests and single pile model tests. Initially, based on the mechanical parameters of strongly weathered granite, 10 groups of similar material samples were prepared using iron concentrate powder, barite powder, and quartz sand as aggregates, with rosin and alcohol as the cementing agents and gypsum as the modulating agent. Through triaxial testing and range and variance analysis, it was determined that the binder concentration has the most significant impact on the material properties. Consequently, Specimen 1 was selected as the simulation material. In the model test, the strongly weathered granite stratum was simulated using the ratio of Specimen 1. A horizontal load was applied using a pulley weight system, and the displacement at the top of the pile was measured with a laser displacement meter, resulting in a horizontal load-displacement curve. The results indicated that the pile foundation remained in an elastic state until a displacement of 2.5 mm. Measurements of the horizontal displacement and bending moment of the pile revealed that the model pile behaves as a flexible pile; the bending moment initially increases along the pile length and then decreases, approaching zero at the pile's bottom. The vertical load test analyzed the relationship between vertical load and settlement of the single pile, as well as its variation patterns. This study provides an experimental basis for the design of single pile foundations in weathered granite formations on the southeast coast of Fujian Province and aids in optimizing offshore wind power engineering practices.

Torsional Vibration of Rock-Socketed Piles Considering the Bottom Sediment and Construction Disturbance

Based on the virtual soil pile model, this study investigates the torsional vibration of rock-socketed piles while considering the influence of bottom sediment. First, the bottom sediment is perceived as a virtual soil pile, however, its parameters are still determined according to the characteristics of the sediment. The pile, along with the virtual soil pile, is partitioned vertically into numerous segments in accordance to the stratified characteristics of the rock and soil around the pile. To account for the radial inhomogeneity arising from construction disturbance, the surrounding soil is divided into multiple annular zones characterized by progressively varied soil properties in the radial direction. The governing equations which delineate the soil-pile system under torsional dynamic loading are subsequently formulated and solved to yield an analytical solution for pile complex impedance. After ensuring reliability, the established analytical solution is employed to examine the coupling effect of bottom sediment parameters, pile parameters, and construction disturbance on the torsional vibration characteristics of rock-socketed piles.

A new calculation method for the response of active-passive bridge piles considering pile-soil interface friction

The pile foundation of bridges under unregulated surcharge loads experiences a complex force pattern, which is subject to active loads and passive loads. In this paper, a more comprehensive calculation method for the response of active-passive piles was proposed, which considered the effect of pile-soil interface friction and soil stress states on the passive loads. First, the Ito theory was improved by adopting the adhesion c a and external friction angle φ a to characterize the pile-soil interface friction. Then, the soil around the pile in elastic, elastoplastic, and plastic flow states was considered to calculate the variation of the passive load. Finally, a nonlinear p-y curve was introduced to establish the calculation model of active-passive piles, and the finite difference program CPAPP was prepared for the solution. The results show that the pile response calculated by CPAPP is consistent with the field measurement, indicating that the proposed calculation method has high accuracy. When the soil is in an elastic state, the pile-soil interface friction does not affect the passive load. When the soil is in a plastic state, the passive load is closely related to soil strength parameters and pile-soil interface friction parameters.

Centrifuge Modelling of the Load-Deflection Response of Single Piles in Sand Under One-Way Cyclic Lateral Loads

This article aims to present the experimental results of one-way cyclic lateral loading tests on centrifuged small-scale models of piles in sand, carried out in the IFSTTAR centrifuge, center of Nantes (France). After a literature review, the pile models, their instrumentation, the experimental devices, as well as the construction of the sand mass were described. Cyclic P-Y lateral reaction curves were derived and the effect of the number of cycles, the soil density, the pile/soil interface roughness, as well as the pile/soil stiffness ratio on their parameters were analyzed. The experimental evolution of the pile top deflection as well as the bending moment along the pile were compared to the usual formulations of the cyclic degradation law.

Bearing Performance of a Helical Pile for Offshore Photovoltaic under Horizontal Cyclic Loading

For an offshore photovoltaic helical pile foundation, significant horizontal cyclic loading is imposed by wind and waves. To study a fixed offshore PV helical pile’s horizontal cyclic bearing performance, a numerical model of the helical pile under horizontal cyclic loading was established using an elastic–plastic boundary interface constitutive model of the clay soil. This model was compared with a monopile of the same diameter under similar conditions. The study examined the effects of horizontal cyclic loading amplitude, period, and vertical loads on the horizontal cyclic bearing performance. The results show that under horizontal monotonic loading, the bearing capacities of a helical pile and monopile in a serviceability limit state are quite similar. However, as the amplitude of horizontal cyclic loading increases, soil stiffness deteriorates significantly, leading to greater horizontal displacement accumulation for both types of piles. The helical pile’s bearing capacity under horizontal cyclic loadings is approximately 60% of that under monotonic loading. With shorter cyclic loading periods, horizontal displacement accumulates rapidly in the initial stage and stabilizes over a shorter duration. In contrast, longer cyclic loading periods lead to slower initial displacement accumulation, but the total accumulated displacement at stabilization is greater. When vertical loads are applied, the helical pile exhibits more stable horizontal cyclic bearing performance than the monopile.

Numerical investigation of pile foundation systems employing an enhanced embedded finite element

The design of large-scale pile foundation systems is routinely assisted by finite element simulations. To a large extent, both the modeling and the computational effort of such analyses are governed by the adopted pile modeling technique. The traditional approach to this problem fully resolves the pile and soil domain employing solid elements, resulting in considerable meshing constraints and high simulation runtimes that may be regarded as unbearable for many practical purposes. As an attractive alternative to circumvent these obstacles, embedded FE models have become increasingly popular in solving this modeling task, mainly due to their flexible meshing procedure and significantly enhanced runtime efficiency. In a preceding contribution, the authors have proposed an extended formulation that provides a rigorous framework to capture soil-structure interaction effects at the physical soil-pile contacts. As a key feature, the implemented combined soil-pile coupling scheme explicitly accounts for endpoint interaction. However, validation studies have been constrained to single pile analyses to date. The present work expands this validation scope to large-scale boundary value problems involving multiple piles and investigates the model performance based on three different case studies. The results are compared to both, measurements and numerical benchmark solutions and provide exclusive insight into the numerical fidelity of the developed embedded FE model, with a view to increasing its potential for take-up in engineering practice.

Laboratory-scale thermo-activated piles under long continuous operation and different mobilised shaft resistance

AbstractThis paper examines the shaft resistance mobilisation ratio as a predictor of cumulative displacement of small-scale floating and end-bearing energy pile foundations subjected to vertical compressive loads embedded in dry sandy soils. A reduced friction model pile was subjected to different mechanical loads and two long-duration, cyclic heating/recovery temperature changes. The pile, soil and container temperatures, pile strains, and vertical displacements are monitored, analysed, and discussed. The results further validate numerical analyses that propose the shaft resistance mobilisation ratio as a variable to identify thresholds above which permanent cyclic thermo-induced deformations may occur. Overall, the experimentally observed responses indicate incremental deformations as the shaft resistance mobilisation ratio increased. The results also suggest that a mobilisation ratio of 66% could be a potential conservative lower-bound limit that could control the increment of thermal-induced vertical displacements in the long term under free pile head conditions. This suggests that a performance-based design would be a reasonable approach for energy piles, and monitoring programs should be set in the field before loading and thermo-activation.

A Transparent Soil Experiment to Investigate the Influence of Arrangement and Connecting Beams on the Pile-Soil Interaction of Micropile Groups.

The use of a micropile group is an effective method for small and medium-sized slope management. However, there is limited research on the pile-soil interaction mechanism of micropile groups. Based on transparent soil and PIV technology, a test platform for the lateral load testing of slopes was constructed, and eight groups of transparent soil slope model experiments were performed. The changes in soil pressure and pile top displacement at the top of the piles during lateral loading were obtained. We scanned and photographed the slope, and obtained the deformation characteristics of the soil interior based on particle image velocimetry. A three-dimensional reconstruction program was developed to generate the displacement isosurface behind the pile. The impacts of various arrangement patterns and connecting beams on the deformation attributes and pile-soil interaction mechanism were explored, and the pile-soil interaction model of group piles was summarized. The results show that the front piles in a staggered arrangement bore more lateral thrust, and the distribution of soil pressure on each row of piles was more uniform. The connecting beams enhanced the overall stiffness of the pile group, reduced pile displacement, facilitated coordinated deformation of the pile group, and enhanced the anti-sliding effect of the pile-soil composite structure.

Assessment of interfacial friction angles of sand-structural materials

This research evaluates the interfacial friction angles of sand-structural materials (i.e. concrete, steel, and wood) from direct shear and model pile tests data. Some variable parameters are considered for performing laboratory tests such as shearing rates (0.05, 0.5, 1.0, 2.0, and 2.5 mm/min.), pile diameters (38.1, 76.2, and 101.6 mm), and normal stresses (27, 55, and 81 kPa). The validated shearing rates are found to be 8.7% and 4.3% in cases of direct shear and model pile tests respectively, which may represent a good accuracy of experimental tests. According to the direct shear test results, the interfacial sand-concrete and internal friction angles are equal at shearing rate of 2 mm/min. The interfacial friction angles are increased with the increment of pile diameters because of slip dilation impact of small diameter pile. The interfacial friction angle of sand-wood pile shows the higher value because of lower self-weight and stiffness of wood compared to the other structural materials. There is a scope for further research by conducting numerical analysis and deriving analytical formulations for obtaining explicit solution.

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.

Model Test Study on the Bearing Mechanism of Inclined Variable Cross-Section Piles Using Transparent Soil

In view of the influence of the inclination and variable section on the pile stability and bearing capacity, this paper introduces particle image velocimetry (PIV) technology, and designs a transparent soil visualization model test. The experimental results show that, when the pile has a variable cross-section and inclination angle, the friction resistance on both sides of the pile increases. The vertical-load-carrying capacity of the 2% and 4% inclined piles with a variable cross-section is greater than that of the piles with inclinations greater than 8%. For model piles with the degrees of inclination of 2% and 4%, the variable-section inclined piles with diameters of 17 mm and 15 mm show significantly less settlement than the equal-section inclined piles. For the model pile with an inclination of 8%, the settlement of the inclined piles with a variable cross-section diameter of 17 mm is slightly smaller than that of the equal cross-section inclined piles. The change in variable cross-section and inclination angle has a large effect on the soil displacement around the pile, and the conclusions of this paper can provide guidance for the engineering application of variable cross-section piles.

The impact of different business models on the environmental and economic benefits of public charging facilities

ABSTRACT This paper explores the impact of different charging pile business models on their economic and environmental benefits. Firstly, this paper analyzes the cooperation and competition relationships among the stakeholders under three charging pile business models, and their impact on the whole process of charging pile from design, production, operation to recycling. Secondly, this paper establishes a social economic benefit evaluation model and a life cycle carbon emission evaluation model based on the differences of charging pile in quality, cost, life span and high-value component recycling rate under different business models. Finally, this paper conducts a case analysis of the economic and environmental benefits of three business models combined with China’s actual situation. The research results show that the economic and environmental benefits of each party in the three business models are closely related to the quality, cost, life span and high-value component recycling rate of the charging pile. Among them, the life span of the charging pile has the greatest impact on its economic and environmental benefits. The higher the recycling rate of high-value components, the more conducive to improving its economic and environmental benefits. The research results will provide reference for policy makers and EVCI investors.

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.

Effectiveness of the Sustainable Manure Pile Model for Ammonia Emission and Soil

In order to reduce odor emissions and surface water pollution while storing manure in field heaps near a barn, there is a challenge in properly designing manure-storage areas. Therefore, it is important to assess what solutions and conditions, considering environmental requirements, should be considered when storing manure in field heaps. The goal of the research is to determine the impact of various factors on the risk of nutrient leaching, soil, and gas emissions from solid manure heaps, considering climatic factors in the environment. Through various scientific studies, a manure pile model has been developed and evaluated for its impact on the risk of potential leaching and odor emissions (using hyperspectral gas emission analysis mass flow method) from manure and the dynamics of the 0–80 cm soil layer properties (nitrate (N-NO3) and nitrite (N-NO2), ammonia (NH3), mineral, and total N). Based on the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania. An optimal new manure heap model has been identified—a layer of not less than 20 cm of compacted straw (density 150–200 kg m−3) or a 10 cm layer of peat for absorbing manure slurries is formed on the soil surface, the manure heap is surrounded by an earth embankment not less than 30 cm high, the manure heap is covered with a layer of finely chopped straw not less than 10 cm thick, or 5 cm of sawdust, or 5 cm of peat. The manure is stored in the heap for 6–12 months. Following the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania, applicable to the northern part of the temperate climate zone and applying similar requirements to the relevant countries.

An Approach of BIM-Based Dynamic Adaptive Zoning for Group Piles Construction Multi-Work Areas

In large-scale pile foundation drilling projects, the absence of digital work area management hampers dynamic construction management, affecting efficiency. This article explores multi-work area management during pile foundation drilling using a BIM parameterized model, focusing on informatization. The results indicate the following: (i) A dynamic zoning method for pile foundation construction using BIM models was developed to support information management systems and address resource allocation challenges amid dynamic construction team changes. (ii) Adaptive zoning methods were proposed, incorporating the dynamic adjustment of construction work areas, including the division of virtual work areas and adaptive adjustment of pile foundation partition parameters. (iii) Work area modeling and zoning were applied on site, with pile foundation modeling aligning with engineering design distribution, and work area zoning accurately reflecting the on-site construction status. (iv) This method enables adaptive synchronization between pile foundation model attributes and work area information, integrating zoning management into the information system to enhance the construction unit’s information management system and digital management level.

Displacement and Internal Force Response of Mechanically Connected Precast Piles Subjected to Horizontal Load Based on the m-Method

Mechanically connected precast piles are a type of precast piles that utilise snap-type mechanical connectors to restrain the pile ends of two identical or different precast piles at the top and bottom so as to quickly realise the purpose of the connection. However, the gap problem in the connectors of mechanically connected piles can lead to uneven and uniform deformation of the piles under horizontal loading, resulting in additional displacements and rotation angles of the piles at the connection. Solving the problem of calculating the internal force response of discontinuous deformed piles is a prerequisite for promoting and applying mechanically connected precast piles. Firstly, the theoretical derivation of mechanically connected piles with fixed constraints at the pile bottom is carried out. Secondly, the pile response equations of mechanically connected piles are established, and the theoretical solutions of pile displacement and internal force response of mechanically connected piles under horizontal loading are derived. Thirdly, the pile-soil model of the test pile is established using ABAQUS software (ABAQUS 2016) in combination with the design data of the test pile. The numerical simulation displacements and angles of rotation are compared with the test results. Finally, the theoretical and numerical simulation displacements and internal forces of the ordinary pile and the mechanically connected pile are compared. The relative errors of the displacements and angles of rotation of the established pile-soil model are less than 10%, indicating that the established model has good accuracy. The relative errors of the theoretical and numerical simulation displacements and internal forces of the mechanically connected pile are less than 10%, proving the correctness of the theoretical calculation by the m-method. This study can provide effective theoretical support and methodological guidance for the displacement and internal force response of discontinuous piles.

Novel analytical approach for vertical dynamic response of floating pile groups based on a fictitious soil pile model

A novel analytical model for the vertical dynamic response of floating pile groups is established based on a fictitious group soil pile model (FGSP). Analytical solutions of the pile-to-pile interaction factor and dynamic impedance for the FGSP are obtained by combining the superposition and matrix transform methods. The obtained solutions are then validated by comparison with model test results and published analytical solutions. A numerical analysis is further performed to examine the effects of pile and soil parameters on the dynamic response of the FGSP. Results indicate that the effects of pile end soil on the pile-to-pile interaction factor and dynamic impedance of the FGSP are significant. Consequently, the established novel analytical model has better applicability to the dynamic problems of floating pile groups due to its consideration of the effects of pile end soil.

Effects of disc overhang diameter on the uplift bearing capacity of new-type concrete expanded-plate pile groups

The disc overhang diameter can significantly affect the uplift bearing capacity of new concrete expanded-plate pile groups, affecting their design and practical applications. Accordingly, this effect was investigated considering the failure laws of the soil surrounding various pile types and groups. Based on the uplift bearing capacities of single and double piles, a finite element simulation was adopted to establish models for the four-, six-, and nine-pile groups. The relationship between the disc overhang diameter and uplift-bearing capacity of each pile group was explored: as the disk overhang diameter increased, the uplift-bearing capacities of the pile groups increased; however, this relationship is nonlinear. The optimal disc overhang diameter was determined as 1.5–1.75 times the pile diameter. For a constant disc overhang diameter, corner piles have a greater uplift bearing capacity than side piles in the six-pile group, and a greater uplift bearing capacity than the side and center piles in the nine-pile group. Thus, the pile-group effect depends on the pile position. The uplift bearing capacity did not increase linearly with the number of piles, and the average uplift bearing capacity of a pile in a pile group was less than that of a single pile. Therefore, the uplift bearing capacity of the pile groups decreased as the number of piles increased. The reliability of the simulation was verified via visual testing of a small-scale half-cut pile model.