Behavior Of Piles Research Articles

A new p-y model for soil-pile interaction analyses in cohesionless soils under monotonic loading

The most widely used analysis method for the laterally loaded pile problem is the Winkler spring approach. Although researchers have proposed nonlinear formulations for the p-y curves, the contribution of the soil nonlinearity has not been thoroughly studied. The main drawback of the current approach is the use of a single stiffness in the p-y formulation. This study investigates the laterally loaded pile problem by employing the pressure-dependent hardening soil model with small-strain stiffness (HS-Small Model), where the degree of soil nonlinearity is better integrated. The parametric analyses are performed on the verified model for various pile and soil properties. A new p-y model is proposed for pile behaviour under monotonic loading based on the numerical analysis results. The model includes the initial stiffness, ultimate soil resistance, and degree of nonlinearity parameters. The validity of the proposed model is demonstrated by simulating a centrifuge and two field tests from the literature. The proposed model accurately accounts for soil nonlinearity and significantly improves the estimation of lateral displacements.

Thermomechanical Analysis of Energy Piles Using a Load-transfer Approach Considering Soil Coupling Effects

Energy piles are inevitably subjected to thermomechanical loads due to their dual role of utilizing geothermal energy and supporting structural loads. The load-transfer approach is a suitable predictive method for addressing the analysis and design of energy piles, but it generally does not properly consider the continuity and deformation behavior of the soil mass. This study presents experimental and analytical investigations on the thermomechanical behavior of full-scale energy piles. A new thermomechanical load-transfer approach allowing consideration of the soil coupling effects was proposed by involving the soil deformation and the soil-pile interface behavior. Through comparative analysis with experimental data, the proposed method (with soil coupling effects) demonstrated superior predictive accuracy compared to the existing method (without soil coupling effects). In this field condition, ignoring soil coupling effects could result in an underestimation of nearly 48.8% of pile head settlement. The validated method was further used to analyze the thermally induced cyclic behavior of energy piles under various mechanical load levels. The results indicated that the thermally induced response of energy piles was directly associated with the level of the head load. The energy piles under higher axial loads may show irreversible thermomechanical behavior when subjected to cyclic thermal loading.

Static behavior of piled raft foundation in clay

Abstract Wall piles supported with anchors are considered one of the most prevalent types of engineering support. This research includes studying the behavior of wall piles through a numerical parametric study using the FE-method program (PLAXIS 2D). The study includes the most influencing factors such as the angle of the inclination, the vertical spacing between the rows of anchors, and the distance of the first row of anchors from the ground surface. The effects of these factors on the stability of the wall were studied. Optimal positioning of the anchors is crucial, as it maximizes their effectiveness and contributes significantly to reducing the overall construction costs. The use of a guys queue for the economic aspect saves the cost of executing two guys queue because the effect of having two rows does not significantly change the transfer values. The optimum angle of inclination of the tensioner row is 15° in favor of safety, and as it gives good stability of the wall to the wedge wall, with an increase in this angle, the horizontal movement decreases. The first optimum dimension for a row of guys from the horizontal surface of the earth is O = 25%H. Decrease the values of horizontal movement of the wall by increasing the angle of friction.

Stress effects due to different installation methods for pipe piles in sand

Impact-driven pipe piles are commonly used in offshore structures, but vibratory driving is becoming more popular due to advantages regarding noise emissions, material fatigue and installation time. In offshore practice, crane-guided vibratory driving is used for maximum control over the installation process. Regarding the load-bearing behaviour of piles, the influence of the installation method is currently subject to research. To contribute to this question, comparative scale model investigations were carried out on impact-driven, jacked and vibratory-driven piles in dense sand. The tests focused on variations of vibratory installation parameters, including crane-guided and free vibratory driving. Based on measurements at the pile and in the soil, the influence of dynamic pile motions on the soil stress development could be analysed. The well-known increase of radial effective soil stresses due to impact driving could be reproduced. The tests showed that the same effects could be evoked by free vibratory driving if certain vibration parameters were met. Increased soil stresses may be beneficial for the lateral or axial pile behaviour, but can cause problems regarding drivability. A sequential application of crane-guided and free vibratory driving may optimise both the installation process and the bearing behaviour.

Experimental and numerical study on thermo-mechanical behaviour of energy pile under different constraints

Thermo-mechanical (TM) behaviour of energy pile (EP) is strongly affected by the pile constraints. The influence mechanism of different constraints on TM behaviour of EP should be revealed. In this paper, the model experiments in laboratory are carried out to research effects of pile end constraints and sand compactness on TM properties of EP. The research results display that the strain of end bearing pile increases gradually along pile depth due to the larger constraint at the pile tip, while the strain distribution of friction pile is large at both ends and small in the middle. Compared with friction pile, the end bearing pile has larger pile tip soil pressure and smaller side friction of pile. The displacement change of EP decreases during the operation in summer mode after applying 0.5 kN load on the pile top. The displacement of end bearing pile can restore to 0 mm, while the friction pile has a settlement of −0.028 mm. In winter mode, both the end bearing pile and friction pile produce unrecoverable settlement, and applying load on pile top will further aggravate the settlement amplitude. As for influence of sand compactness, compared with loose sand, the dense sand has greater thermal conductivity which benefits to the thermal efficiency of EP. This results in smaller pile excess temperature and recovery rate of surrounding soi1 temperature. Accordingly, the pile top displacement and strain also decrease due to small temperature variation, but the pile side friction and side soil pressure increase. The mechanical properties of EP under the condition of different pile-soil parameters are simulated by a 3-D numerical model, which is validated by experiments. It is shown that when the Poisson's ratio of the soil increases from 0.2 to 0.4, the top displacement of the pile increases from −7.35 mm to −8.76 mm, which attributes to the increase in the lateral deformation of the soil, resulting in a decrease in the soil constraint on the pile. Although the distributions of pile side friction along the pile depth are basically the same for different poisson's ratios, there are differences at the pile tip. Also, increasing the pile-soil interface friction coefficient will result in the enhancement of constraint and pile side friction and the decrease of pile body displacement and thus improve the mechanical properties of EP. The study helps to reveal the influence mechanism of various constraints on the TM properties of EP and can provide reference for the safe and efficient operation of EP.

Numerical analysis of horizontal bearing capacity of pile in clay slope

In this study, a series of numerical calculations were performed to investigate the lateral behavior of piles in slopes and in horizontal ground. First, a numerical model is created and then verified by comparing the numerical results with the results of model tests. The numerical results agree well with the results of model tests. Second, numerical calculations of different slopes were conducted to explore the effect of slope angle on the horizontal displacement of pile and bending moment. Then, the effect of slope angle on the foundation stiffness proportional coefficient m is investigated. The stress distribution of soil around the pile and the deformation of pile at different slope angles are also compared. Finally, the p–y curves of the different slope angles are compared. An improved p–y method is proposed to consider the effect of slope angle based on the numerical results. The results show that the bearing capacity of piles decreases with an increase in slope angle. The horizontal displacement of pile nonlinearly decreases along the pile body with the depth of pile. The bending moment of piles increases along the pile body with an increase in pile depth, and until 0.5 times of the pile length, the bending moment reaches the maximum value. As the slope angle increases, the maximum of bending moment tends to decrease. The distance from the slope toe to the pile section has a little influence on the pile bending moment and horizontal displacement. With an increase in slope angle, the horizontal foundation coefficient m gradually decreases.

An Experimental Study on the Lateral Behavior of Piles in Unsaturated Sand Under Monotonic, Cyclic and Post Cyclic Loading

An Experimental Study on the Lateral Behavior of Piles in Unsaturated Sand Under Monotonic, Cyclic and Post Cyclic Loading

Pullout Behavior of Suction Piles in Saturated Sand Subjected to Combined Vertical and Horizontal Loading – Centrifuge and Finite Element Analysis

Suction piles have increasingly been considered as foundations for offshore facilities. In this study, the pullout behaviors of suction piles embedded in saturated sand subjected to combined vertical and horizontal loading at various inclination angles and pad-eye positions are investigated carrying out centrifugal tests and finite element (FE) analyses. The ultimate pullout capacities obtained from the model tests and FE analyses both increased as the inclination angle was close to 0° and the pad-eye position approached 75% of the pile length from the lid. This is associated with the increase of the passive earth pressure and friction between the soil and suction pile while the pile is pulled out. The failure envelopes were suggested depending on pad-eye positions to improve the design approach for offshore foundations. The optimal pad-eye positions for catenary and taut-leg mooring systems were then investigated by additional FE analyses to demonstrate the practical implications. For both mooring systems, the largest ultimate pullout capacity was obtained when the pad-eye was located at 75% of the suction pile length below the lid. The ultimate pullout capacity of the catenary mooring system was determined to be 1.94 times that of the taut-leg mooring system under the same conditions.

Numerical investigation of the carrying capacity of single polyurethane foam pile in clay and sand soils

The definition of soil stabilization is a method to enhance the engineering properties. Polyurethane grout is one of the least expensive methods and can be used in construction. Polyurethane injection resin systems for crack injection, slab lifting, soil stabilization, leak sealing, and structural crack repair have been used for the last two decades. Polyurethane foam hasn't been used or understood as a loaded structural element in soils like as embedded piles. In this piece of work, a trial was made to numerically study the behavior of polyurethane foam when used as piles embedded in the clay and sand soils. Plaxis 3D software was adopted to carry out this study. Polyurethane piles of varying diameters and lengths were modelled as embedments in the clay and sand soil, and then incremental loads were applied. Moreover, the study involved the behavior of polyurethane piles when the clay strength was increased. The results indicated that embedded pile resistance to loading increased with the increase in length and pile diameter. When the loading results of polyurethane foam embedded in loose sand are compared with the loading results of piles in soft clay, the ultimate capacity of piles in loose sand, was much higher than that in soft clay. The results also indicated that the polyurethane pile load-carrying capacity increased when L/D ratio decreased for both soft and stiff clay. In this study concrete piles in clay and sand soil were modelled to examine the percentage of loading capacity of concrete piles to that of polyurethane piles for clay and sand soil.

Machine Learning Models to Evaluate the Load-Settlement Behavior of Piles from Cone Penetration Test Data

Machine Learning Models to Evaluate the Load-Settlement Behavior of Piles from Cone Penetration Test Data

Seismic Failure Mechanisms of Concrete Pile Groups in Layered Soft Soil Profiles

So far, little attention has been paid to the investigation on the seismic failure mechanisms of flexible concrete pile groups embedded in the layered soft soil profiles considering the material non-linearities of soil and concrete piles. The purpose of this study is to investigate seismic failure mechanism models of flexible concrete piles with varied groups in silt layered loose sand profiles under horizontal strong ground motions. Three-dimensional finite element models of the pile–soil interaction systems, which include nonlinearities of soil and concrete piles as well as coupling interactions between the piles and soil, were created for Models I, II, and III of the soil domains, encompassing 1x1, 2x2, and 3x3 flexible pile groups with diameters of 0.80 m and 1.0 m. Model I consists of a homogenous sand layer and a bedrock, Models II and III are composed of a five-layered domain with homogeneous sand and silt soil layers of different thicknesses. The linear elastic perfectly plastic constitutive model with a Mohr–Coulomb failure criterion is considered to represent the behavior of the soil layers, and the Concrete Damage Plasticity (CDP) model is used for the nonlinear behavior of the concrete piles. The interactions between the soil and the pile surfaces are modeled by defining tangential and normal contact behaviors. The models were analyzed for the scaled acceleration records of the 1999 Düzce and Kocaeli earthquakes, considering peak ground accelerations of 0.25 g, 0.50 g, and 0.75 g. The numerical results indicated that failure mechanisms of flexible concrete groups occur near the silt layers, and the silt layers have led to a significant increase in the spread area of the damaged zone and the number of damaged elements.

Effect of Sloping Ground on the Pile Behaviour Under Varying Static Lateral Loads

Effect of Sloping Ground on the Pile Behaviour Under Varying Static Lateral Loads

Physics‐informed neural networks for large deflection analysis of slender piles incorporating non‐differentiable soil‐structure interaction

AbstractPhysics‐informed neural networks (PINN) is an emerging machine learning technique and has been applied in different areas successfully. To benefit pile analysis from this innovative technique, this paper addresses several problems that arise when extending PINN to the large deflection analysis of slender piles accounting for nonlinear Soil‐Structure Interaction (SSI). The governing equations for the structural behavior of piles, considering geometric nonlinearity, are elaborated at first, based on which a PINN framework is constructed correspondingly with a model training process. A series of normalization factors are introduced to the loss function to enhance model training stability. Additionally, a regression‐based soil resistance estimation is developed to prevent non‐convergence and instability that may occur during the model training when encountering non‐differentiable SSI. Extensive examples are provided to validate the robustness and accuracy of the proposed analysis method for piles under complex geological conditions. Furthermore, several case studies are conducted, revealing the necessity of appropriate loss normalization and the effectiveness of regression‐based estimation for reflecting non‐differentiable functions in the PINN study.

Experimental Evaluations of Model Piles Subject to Inclined Loading in Sand

The structures that subjected to varying loads are supported by pile foundations. These loads consist of inclined and vertical loads. The main objective of this work is to experimentally investigate the effects of an inclined load on the lateral pile reaction and axial pile displacement for piles found in cohesionless soil. For this purpose, the slenderness ratios of model steel piles are varied by values of 11, 14, and 17. Moreover, the pile shapes involved in this study are H-pile, closed end circular and square. The experimental tests were conducted in sandy soil. However, the load inclination angle included in assessing the pile behavior were 0, 30, 45, and 60 from the vertical. In order to study the above parameters on the behavior of model pile, thirty-six experimental tests were carried out. Several findings indicated that the lateral pile deflection was highly influenced by increasing the load inclination. Further, the load inclination effect on the pile's ultimate bearing capacity is high which leads to a reduction in the pile's capacity. Additionally, the vertical displacement of pile is less than horizontal displacement when the pile is subjected to an inclined load of 45° and the model fails by horizontal displacement.

Effect of soil-pile contact parameters on pile bearing capacity value

The soil and foundation elements are fundamental to the behavior of a structure. When the foundation soil has a low capacity, it is necessary to transmit the loads to a deeper and more resistant layer, using deep foundations. A pile load test is a field measurement of the bearing capacity (vertical or horizontal) of a foundation element. In addition to a physical model of a load test, the use of computational tools can bring additional understanding. In order to analyze the responses obtained by numerical models compared to field test results, tools that use Finite Element Methods (FEM) and that have a series of constitutive models become a great alternative. This paper aims to study the behavior of Continuous Flight Auger (CFA) piles, aiming to understand the soil-pile interaction regarding the effect of soil-pile contact parameters on pile bearing capacity value. In this way, experimental data from three load tests were compared with numerical simulations using the Mohr-Coulomb constitutive model. Also, a parametric study was completed based on the collected soil data from the literature of the region that most affected the settlement behavior of the load pile. It was concluded that there is a direct and significant influence of the friction coefficient on the pile bearing capacity. In addition, by incorporating more real soil data and parameters representing its actual formation, the results of the pile load test simulation can be taken as an alternative to estimate the ultimate capacity of a vertically loaded pile in the absence of the static load test, which has been widely observed in engineering practice.

Numerical modeling of open-ended piles

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

Investigation of laboratory and field tests of piles installed by displacement technology

When compared to conventional pile systems, the Drilled Displacement System (DDS) and Continuous Flight Auger (CFA) piles offer advantages in terms of improved load-carrying capacity, quicker installation, and less spoil generation. In this article, experiments on miniature piles built utilizing the Drilled Displacement System (DDS) and Continuous Flight Auger (CFA) technologies in a soil-filled test tank are described. For the study, model piles with dimensions of 20 mm in diameter and 300 mm in length were used, scaled at 1/20. The model piles are subjected to static loading, and throughout each phase of the loading process, the relevant displacements are measured. For both DDS and CFA piles, the analysis's findings on load-settlement curves and estimates of ultimate bearing capacity were compared. According to the study, the DDS piles outperformed the CFA piles in terms of load-carrying capacity. Additionally, full-scale field tests with static loads were performed on DDS-drilled piles with dimensions of 400 mm in diameter and 6 m in length. The field test's load-settlement response exhibits good agreement with the model testing. Overall, the study's findings offer insightful information about the behavior and performance of DDS piles that may be used to improve the design and installation of these piles in various soil types.

Experimental Modelling of Helical Piles Subjected to Axial Loading

In the construction sector, axial loads have traditionally been supported by piles. There hasn't been sufficient comparative study related to the economics and viability aspects of conventional and helical piles up to this point in natural soil condition. The current study was conducted to test the behavior of helical piles subjected to axial loading and the results were compared with the conventional pile counterpart. For this, a total of eighteen experiments were performed with varying number of helical piles either single or multi helical piles in a raft. Helical piles were penetrated into ground, vertical load of 512 kg was applied and the settlements were recorded with the gauges installed. The reduction in settlement was found to increase due to increasing the number of piles, inter distance between the piles and increasing the number of helices. Nine double helical piles were observed to reduce settlement by 80.5% when compared to nine conventional piles. Due to the smaller number of piles needed to support the applied axial load when employing helical piles as opposed to conventional piles, the cost was greatly lowered.

Comparison of bearing capacities of model drilled micro piles using DDS and CFA technologies

Drilled piles installed using CFA (Continuous Flight Auger) and DDS (Drilled displacement system) technologies are relatively new construction products in the market of Kazakhstan for the last 15 years, but already today the technology has a significant practical value in the construction of the cities of Astana, Almaty and other regions. This article presents model tests of bored piles installed using Drilled Displacement System (DDS) and Continuous Flight Auger (CFA) technologies on a volumetric bench. For testing we used 1:20 scale, piles diameter was 20 mm, length was 300 mm. Drilling was performed using augers that were prepared in advance through a 3D printer. The load on the model piles was applied in steps of 39 N up to the ultimate load of 391 N. Based on the results of the study, the «settlement-load» plots of the DDS and CFA model piles were obtained, as well as a comparison of the bearing capacity of these piles by static test method. Based on the study, it was found that the DDS piles exhibit good bearing capacity performance compared to the CFA piles. Overall, the results of the study provide valuable information on the performance behavior of DDS and CFA piles, which can be used to optimize their design and installation in different soil types.

Experimental Study on Thermo-Mechanical Behavior of a Novel Energy Pile with Phase Change Materials Using Fiber Bragg Grating Monitoring

The combination of phase change materials (PCMs) with building materials is a flourishing technology owing to the low-temperature change of the materials during phase change and the potential for enhanced heat storage and release. In this study, a new type of PCM energy pile, in which 20 stainless steel tubes (22 mm in diameter and 1400 mm in length) filled with paraffin were bound to heat exchange tubes, was proposed. An experimental system monitored by a fiber Bragg grating (FBG) to study the thermo-mechanical behavior of energy piles and surrounding soil was established. Both the PCM pile and the ordinary pile, with the same dimensions, were tested under the same experimental conditions for comparison. The results indicate that the temperature sensitivity coefficient calibration results of the FBG differ from the typical values by 8%. The temperature variation is more obvious in the ordinary pile and surrounding soil. The maximum thermal stress of the ordinary energy pile is 0.5~0.6 times larger than that of the PCM pile under flow rates ranging from 0.05 m3/h to 0.25 m3/h. The magnitudes of the pore water pressure and soil pressure variations were positively correlated with the flow rates.