Model Piles Research Articles

Behaviors of Inclined Single Piles and Pile Groups Subjected to Vertical and Horizontal Loads Based on Physical Model Tests in Sand

Inclined pile foundations with high inclination angles, subjected to both vertical and horizontal load, are increasingly used due to the advancement in installation technology. This study aimed to characterize the bearing capacities and deformation behavior of inclined pile foundations subjected to vertical and horizontal loads in laboratory-scaled testing. In a series of pile-modeled tests, the stainless-steel pile as a model pile, the single pile and the symmetrical 2 × 1 pile group were installed in dense sand at 0°, 10°, 20°, and 30° of inclination angles. The experiment in an inclined single pile subjected to vertical load aimed to minimize the eccentricity effect. The results showed that the optimal pile inclinations for vertical load were 10° and 20° for single pile and pile group, respectively. For optimal pile inclinations of horizontal load, they were between −10° to −20° and 20° for single pile and pile group, respectively. The ratios of the ultimate horizontal load to the ultimate vertical load (Quh/Quv) ranged from 0.02 to 0.19 and 0.15 to 0.23 for the single pile and the pile group tests, respectively. The group efficiencies for vertically loaded pile groups ranged from 58%–139% and 107%–130% for horizontal loading.

Fictitious soil pile model for dynamic analysis of pipe piles under high-strain conditions

Fictitious soil pile model for dynamic analysis of pipe piles under high-strain conditions

Experimental Study on the Negative Skin Friction of Piles in Collapsible Loess

The collapsible loess is widely distributed in western China. The special structure and water sensitivity of loess lead to the complex negative skin friction mechanism in pile foundations. Previous studies mainly focused on the negative skin friction of pile foundations and treatment measures, such as casing and coating methods. However, few studies have focused on the influence of the negative skin friction on the settlement and bearing capacity of piles in collapsible loess, especially environmentally friendly methods that can reduce the negative skin friction. In this study, a series of non-immersion and immersion experiments was conducted to investigate the settlement, axial force, and side friction resistance of piles in loess soil under controlled conditions. The results showed that under the non-immersion condition, the settlement of model piles increased with the increasing pile top load. The axial force gradually decreased along the pile length for piles without casing. The axial force attenuation of the casing section of casing piles was almost negligible due to the isolating frictional resistance effect of casing. The settlement of each soil layer increased with the increase in immersion time, and the process was divided into an initial gradual stage, rapid drop stage, and later gradual stage. Both negative and positive skin friction increased with the increasing immersion time and pile top load, and there was a neutral point. The maximum axial force of piles without casing exceeded the peak load at the pile top. The presence of steel casing reduced the failure of pile foundation in collapsible loess. The research results of this paper provide theoretical support for the application of piles in loess areas.

Influence of Horizontal Loading in Changing the Ultimate Uplift Bearing Capacity of Monopile Foundation of Offshore Wind Turbine

Throughout their lifespan, monopile foundations supporting offshore wind turbines inevitably experience horizontal loads from waves, winds, and currents, resulting in cumulative deformation. It has been believed that deformation caused by horizontal loading weakens the interaction between the pile and the soil, leading to a reduction in the ultimate uplift bearing capacity of the pile foundation. However, there is a scarcity of literature investigating this issue, particularly regarding monopiles used in offshore wind turbine installations. Therefore, this study aims to explore the impact of horizontal cyclic loads on the ultimate uplift bearing capacity of monopile, focusing on the pile–soil interaction. To achieve this, a series of 1 g model tests were conducted on a rigid model pile embedded in silt with varying relative compaction. The test results indicate that the ultimate uplift bearing capacity of the pile is significantly diminished after experiencing horizontal cyclic loading, and the extent of reduction is closely linked to the amplitude of the horizontal deformation. A semi-empirical model is developed to predict the ultimate uplift bearing capacity of the pile foundation following horizontal cyclic loading. The key findings of this study are as follows: (1) The earth pressure in the active zone gradually decreases with an increasing number of cycles, while the earth pressure in the passive zone experiences a slight increase under horizontal cyclic loading. (2) The position of the pile rotation center under horizontal cyclic loading is approximately 0.84 times the depth at which the pile is buried, and this relationship appears to be independent of soil density and cyclic load ratio. (3) The variation of earth pressure corresponding to the horizontal deformation of the pile in the active zone can be divided into three phases: a rapid decline phase, a slow decline phase, and a stable phase. (4) The reduction in the ultimate uplift capacity is influenced by the cyclic ratio and number of cycles but does not appear to have a significant relationship with soil density.

Anomalous Self-Organization in Active Piles.

Inspired by recent observations on active self-organized critical (SOC) systems, we designed an active pile (or ant pile) model with two ingredients: beyond-threshold toppling and under-threshold active motions. By including the latter component, we were able to replace the typical power-law distribution for geometric observables with a stretched exponential fat-tailed distribution, where the exponent and decay rate are dependent on the activity's strength (ζ). This observation helped us to uncover a hidden connection between active SOC systems and α-stable Levy systems. We demonstrate that one can partially sweep α-stable Levy distributions by changing ζ. The system undergoes a crossover towards Bak-Tang-Weisenfeld (BTW) sandpiles with a power-law behavior (SOC fixed point) below a crossover point ζ<ζ*≈0.1.

Application of Physics-Informed Neural Networks for forward and inverse analysis of pile–soil interaction

The application of the Physics-Informed Neural Networks (PINNs) to forward and inverse analysis of pile–soil interaction problems is presented. The main challenge encountered in the Artificial Neural Network (ANN) modeling of pile–soil interaction is the presence of abrupt changes in material properties, which results in large discontinuities in the gradient of the displacement solution. Therefore, a domain-decomposition multi-network model is proposed to deal with the discontinuities in the strain fields at common boundaries of pile–soil regions and soil layers. The application of the model to the analysis and parametric study of single piles embedded in both homogeneous and layered formations is demonstrated under axisymmetric and plane strain conditions. The performance of the model in parameter identification (inverse analysis) of pile–soil interaction is particularly investigated. It is shown that by using PINNs, the localized data acquired along the pile length –possibly obtained via fiber optic strain sensing–can be successfully used for the inversion of soil parameters in layered formations.

Simulation study on coupled heat and moisture transfer in grain drying process based on discrete element and finite element method

In present article, the soybean packed bed was generated based on the Discrete Element Method, and the distribution of radial porosity and airflow path of the packed bed were analyzed. The porosity distribution of the packed bed is not uniform, and it is larger near the wall. However, it is lower near the central axis, resulting in a larger airflow tortuosity in this area. Based on the thermal non-equilibrium principle, the double-diffusion heat and moisture transfer model of grain pile was developed. The double-diffusion model was verified and validated using experimental data from the relative literature on soybean thin-layer drying, and the mean relative deviation was 1.74–4.47% between the simulated and the experimental results. The model was applied to the drying process of soybean packed bed, and the influence of drying air temperature and inlet air velocity on drying was analyzed. It was shown that the moisture transfer rate of soybean is mainly affected by the drying air temperature and the moisture content of soybean. At constant air temperature of 35 °C, 45 °C, 55 °C, and 65 °C, and drying air relative humidity of 17%, 21%, 25%, and 30%, respectively, the drying rates were 0.086, 0.089, 0.093, and 0.098%(d.b.)/min, respectively (within the first 10 min). The drying with the stepwise temperature makes the drying rate curve abnormal. Compared with the constant temperature drying at 45 °C, when the drying air temperature changes from the initial value of 55 °C and 35 °C to the end value of 40 °C and 65 °C, respectively. It was observed that drying the packed bed moisture content to 14.5%(d.b.) saves time as much as 80, 110, and 130 min.

Research on Pile Parameters of Screw Pile based on Horizontal Bearing Capacity

This paper studies the horizontal bearing capacity of screw pile under the limit state of normal use in silty sand soil, simulates the horizontal loading process of screw pile by ABAQUS software, introduces the creation process of the model of screw pile, material attribute selection and finite element mesh division, etc. The influencing factors and variation rules of horizontal bearing capacity, plastic zone of soil mass, failure mode of soil mass and pile deformation mode of screw pile are studied, and a more comprehensive parameter basis is provided for the establishment of prediction formula of horizontal bearing capacity of screw pile. The parameters of screw pile diameter, screw blade diameter and screw blade buried depth are analyzed. It provides some support for the theoretical analysis and engineering practice application of screw pile.

Laboratory Test Study on Pile Jacking Penetration Mechanism Considering Different Diameter and Length Based on Photoelectric Integration Technology

Model tests are carried out on the jacked single piles of different diameters and pile lengths under the model pile of different diameters and pile lengths in clayey soil, which aims to investigate the penetration mechanical mechanism. How to accurately test the pile end resistance and pile side resistance during jacked pile sinking is particularly important. In this paper, a full-section spoke-type pressure sensor, a double diaphragm temperature self-compensating fiber Bragg grating (FBG) earth pressure sensor and a sensitized miniature FBG strain sensor are jointly applied to a single pile penetration model test to test a single pile driving force, pile end resistance and pile body stress during penetration. The test results show that the load transfer performance of test piles will be affected by different diameters, and the axial force transfer capability of a large diameter in the depth direction is better than that of a small diameter since the compacting effect is more obvious. The unit skin friction of the pile increases gradually as the depth increases, which is larger due to the lateral extrusion force increasing as the diameter increases. At the same depth, the unit skin friction of two different diameter piles demonstrates “friction fatigue”, which also decreases obviously as the depth increases. Under the conditions of this test, the maximum frictional resistance of the pile TP1 pile side is about 27.7% higher than that of the test pile TP2. In the static pile sinking process of three test piles in cohesive soil, 50% is end bearing; therefore, there is 50% friction, and the diameter influences the end bearing and the length influences the friction.

Classification of Low-Strain Foundation Pile Testing Signal Using Recurrent Neural Network

The testing of the foundation pile is an important means to ensure the quality of the foundation pile in the construction process, and the low-strain pile test is one of the most commonly used testing technologies. However, in order to ensure that the testing signal is effective and reliable, it is necessary to provide the preliminary judgment results when acquiring the testing signal in the field. In this paper, we propose a data classification method for low-strain pile testing data using a recurrent neural network as the core. In this method, after identification, tailoring, and normalization, the input feature vector with a sequential structure is sent into this model. The model ensures the efficient use of data values while considering the sequential relationship among the data. At last, we designed and produced one complete model pile and six asymmetric model piles, which can form thirteen kinds of testing signals. The optimal application model was selected by the 10-fold cross verification method, and the influence of increasing the input feature dimension on the accuracy was discussed. Finally, compared with the other two methods, this model has the highest accuracy, at 98.46%, but it requires more training parameters and a longer training time.

Soil arching effect of composite piles supporting foundation pits based on mechanical model and photoelastic experiment

In this study, the analytical solution of soil stress behind a composite pile and the arch height of the soil was derived using a mechanical model of a composite pile supporting the foundation pit. The mechanical model was developed based on the theory of uniform load on semi-infinite space in elastic mechanics. The analytical solution was validated through a photoelastic experiment and finite element numerical simulation, and the soil stress behind the composite pile was calculated. The stress visualization of the composite pile supporting the foundation pit with different pile diameters and spacings was realized through photoelastic experiments. The empirical relationship was established between the inner and outer arch heights, load, pile diameter, and spacing. A finite element simulation was performed to examine the influence of small pile diameter and spacing on the soil displacement and lateral stress coefficient. This study provides an important reference for studying the soil arching effect of composite piles supporting foundation pits.

Metamodelling of the load-displacement response of offshore piles in sand

The paper illustrates the development of metamodels of the response of steel piles driven in sand and subjected to pull-out. The metamodels are created for the prediction of the pile tensile capacity and secant stiffness. They were developed using the results of finite element analyses, which made use of finite element models of robustness assessed employing a selection of available data from large-scale model pile tests. Four hundred finite element analyses allowed for the calibration of very accurate metamodels, which were also demonstrated to closely track the outputs of the experimental results. Once calibrated, the metamodels can be used independently from the finite element models they stemmed from. The outcomes of the study show that metamodels of piles response can yield very accurate results within a wide and realistic range of soil-pile configuration, avoiding the laborious implementation and computational cost which underpins the use of finite element models. As the use of metamodels in this context is new, the paper relies on particularly simplified problem, but the procedure could be extended to accommodate modelling features of higher complexity.

Experimental Evaluation of Load Distribution between Piles in Case of Block Failure

In this study, the load distribution of the piles in the pile group was investigated in the case of the pile raft foundations failure under the effect of vertical loads in cohesive soils. For this purpose, loading tests were carried out on model pile groups in the laboratory. In addition, the effects of these conditions on the load distribution between the piles were examined by changing the pile spacing and soil properties. As a result of the experiments, it was determined that the piles in the corner region carried more load than the ones in the center region in small settlement amounts as in the literature. However, it has been determined that as the amount of settlement in the pile foundation increases, the soil between piles behaves like a block and approaches failure, and the piles in the center region of the pile group carry more load. As a result of excessive settlement, a fracture surface formed around the block and therefore the corner piles of the block began to carry less load. It has been determined that failure analyses should be performed considering the load carried by the corner piles after failure due to excessive settlement.

Centrifuge and numerical modeling of h-type anti-slide pile reinforced soil-rock mixture slope

Centrifuge and numerical modeling of h-type anti-slide pile reinforced soil-rock mixture slope

A Time-Dependent Load-Transfer Model for Large Step-Tapered Hollow Piles Based on the Disturbed State Concept

A Time-Dependent Load-Transfer Model for Large Step-Tapered Hollow Piles Based on the Disturbed State Concept

Axial and lateral bearing capacity assessment of bored piles on medium-dense sand and liquefiable potential based on numerical simulation

Liquefaction on bridges can cause structural failure due to loss of soil strength. The Showa Bridge that collapsed in 1964 Niigata earthquake was caused by buckling in piles as the soil layer liquefied and friction losses. In addition, there was a case of Palu IV bridge collapse in Indonesia during the recent 2018 Palu earthquake, which indicated have been affected by earthquakes and liquefaction. This study examines the reliability of the bored pile foundation of the Kretek 2 Bridge in Bantul Regency, Yogyakarta Special Region Province, for axial and lateral bearing capacity. This research method uses the soil structure interaction and 3D numerical simulation by Midas Civil and Midas GTS NX pile modeling. The pile driving analysis and lateral static loading test were also conducted, which can be compared to MIDAS results. For the foundation modeling result, there is an increase in axial and moment forces but a decrease in shear forces during liquefaction. While the lateral displacement increases significantly in the liquefaction state, foundation performance is still stable. Therefore, the foundation of the kretek 2 bridge is sufficient to support axial and lateral load both in a static state and a liquefaction state.

Settlement analysis of ground treated with granular piles using natural and recycled aggregates

Scarce land availability forces humans to build on soft soils, prone to long-term deformation and lacking sufficient shear strength, resulting in potential structural damage. Granular piles (GPs) are suitable for treating soft clay, providing increased load-bearing capacity, reduced settlements, faster consolidation, liquefaction risk elimination, and improved stability for natural slopes and embankments. Traditionally natural aggregates are used as granular material in pile construction, whereas the present study aims to analyze the effect of replacing natural aggregates with some recycled waste aggregates. The main objective of the present study is to numerically investigate the settlement resistance and load-carrying capacity of weak soils by incorporating granular piles made of unconventional aggregates. This numerical analysis considers various granular materials for piles, including natural aggregates (NA), crushed concrete (CC), crushed brick (CB), and industrial waste aggregates like crushed marble (CM) and crushed sandstone (CS). According to the findings of the current study, the use of crushed concrete (CC), crushed brick (CB), and industrial waste aggregates such as crushed marble (CM) and crushed sandstone (CS) in the formation of granular piles led to a notable enhancement in the settlement characteristics and bearing capacity of soft soils. In the current study, some experimental models of locally available sandy soil treated with granular piles are prepared and tested in California bearing ratio (CBR) moulds to investigate their settlement behavior. Granular pile models are prepared of natural & recycled aggregates (CC), and the effect of incorporating cementing agents like - cement and flyash on the settlement behavior of reinforced ground is also investigated. Experimentally, the sandy soil treated with granular piles made of natural and recycled aggregates shows higher resistance towards settlement compared to untreated soil. The resistance towards settlement increases marginally with the incorporation of cementing agents. The optimum value of CBR (80%) is observed for sandy soil treated with a granular pile of natural aggregates with cementing material (3% cement + 6% fly ash) cured for 7 days (TNCF7).

Experimental Investigation of Crack Propagation Mechanism and Load-bearing Characteristics for Anti-slide Pile

Reinforced concrete anti-slide pile is a typical anti-slide installation under horizontal load. Its stress is essentially the cantilever beam working under the combined action of bending moment and shear force. In the process of loading, concrete is accompanied by the generation and expansion of different forms of cracks. In order to reveal the bearing characteristics and crack propagation law of anti-slide pile, the 1:10 scale model of the anti-slide pile in Majiagou landslide treatment project was taken as the object. The mechanical mechanisms of three kinds of the anti-slide piles with different pile lengths were studied. The bending moment and deformation law of three anti-slide piles were obtained. The results show that the pile is easy to crack in the range of 0.5 m above and below the sliding surface. With the increase of cantilever length, the bending moment increases. The development of the maximum crack length and width presents the crack initiation stage, stable stage, and failure mutation stage. Through the monitoring of the length and width of the crack and the judgment of its stage, the working state of the pile can be obtained. The results can provide reference for the optimal design of anti-slide pile in landslide treatment engineering.

Closed-form dynamic stiffness formulation for modal and dynamic response analysis of pile group foundations

A closed-form dynamic stiffness (DS) formulation is proposed for pile group foundations. This model consists of a rigid cap and an arbitrary number of flexible piles. The rigid cap, connecting to all piles, is modeled as a rigid body resting on an elastic foundation. For each pile, a longitudinal soil–pile model and a preloaded Timoshenko beam on viscoelastic Pasternak foundation are adopted to describe the longitudinal and transverse vibration, respectively. The piles can be either friction piles or end-bearing piles, and pile sections surrounded by different soil layers can be easily modeled by the assembly of pile elements with different parameters. The proposed DS formulations essentially use very few degrees of freedom to, nevertheless, describe the broadband dynamic behaviors of complex pile group foundations in a highly accurate manner. The DS formulation is then used for modal and dynamic response analysis. For modal analysis, the Wittrick–Williams algorithm is applied, with the key issue J0 count problems resolved. The proposed method is verified against some existing results. This research provides an exact and highly efficient modal and response analysis tool for pile group foundations, which can be used for the dynamic analysis of pile foundations subjected to earthquake or traffic excitations.

Thermal integrity profiling of cast-in-situ piles in sand using fiber-optic distributed temperature sensing

Defects in cast-in-situ piles have an adverse impact on load transfer at the pile‒soil interface and pile bearing capacity. In recent years, thermal integrity profiling (TIP) has been developed to measure temperature profiles of cast-in-situ piles, enabling the detection of structural defects or anomalies at the early stage of construction. However, using this integrity testing method to evaluate potential defects in cast-in-situ piles requires a comprehensive understanding of the mechanism of hydration heat transfer from piles to surrounding soils. In this study, small-scale model tests were conducted in laboratory to investigate the performance of TIP in detecting pile integrity. Fiber-optic distributed temperature sensing (DTS) technology was used to monitor detailed temperature variations along model piles in sand. Additionally, sensors were installed in sand to measure water content and matric suction. An interpretation method against available DTS-based thermal profiles was proposed to reveal the potential defective regions. It shows that the temperature difference between normal and defective piles is more obvious in wet sand. In addition, there is a critical zone of water migration in sand due to the water absorption behavior of cement and temperature transfer-induced water migration in the early-age concrete setting. These findings could provide important insight into the improvement of the TIP testing method for field applications.