Displacement Piles Research Articles

Dynamic Response Analysis of Anchor Piles for Marine Aquaculture under Cyclic Loading

The anchor pile is widely used in marine aquaculture, and its uplift resistance capacity determines the safety performance of the marine aquaculture structure. Cyclic loads such as wind, waves, and currents in the marine environment affect the uplift resistance capacity of anchor piles. By carrying out a cyclic loading model test of anchor piles for marine aquaculture, the influence of loading amplitude, initial tension angle, and other factors on the uplift resistance of anchor piles was investigated. The experimental results showed that with an increase in the loading amplitude, the cumulative displacement and elastic displacement of the anchor pile under vertical and oblique loading increase, and the stiffness of the soil around the anchor piles decreases. The stability of the anchor piles is reduced. When the loading amplitude is the same, with the increase in the initial loading angle, the lateral cumulative displacement of the anchor pile increases. Meanwhile, the vertical cumulative displacement decreases, the stiffness of the soil around the anchor pile decreases, and the stability decreases.

Dynamic Response of Cement–Fly Ash Mixed Pile Composite Foundation Under Wave Load

CFMPs (cement and fly ash mixing piles) are used to reinforce fly ash foundation to solve the problem of a large amount of fly ash accumulation in coastal areas. CFMP-fly ash composite foundation is used as the foundation of coastal and coastal engineering. Through the indoor model test, the bearing characteristics and load transfer mechanism of CFMP-fly ash composite foundation under wave load were investigated. The results show that with the increase of wave load, the horizontal resistance of the fly ash stratum increases gradually, the soil resistance moves down, and the level of resistance shows nonlinear characteristics. The pile bending moment, pile displacement, and horizontal resistance of the CFMP composite foundation are concentrated in the upper pile and fly ash stratum, which can improve the ability of the composite foundation to resist horizontal load by improving the physical and mechanical properties of the upper fly ash stratum. Through the calculation of the load–displacement curve, it is found that the measured displacement value is closer to that obtained using the p–y curve method (a method for solving nonlinear lateral resistance of piles). The hysteretic curve area of cyclic loading decreases with the increase of cyclic number. The accumulation of elastoplastic deformation of pile shows that the properties of fly ash gradually change to elastic stage, cyclic loading can reduce the horizontal deformation modulus of composite foundation CFMP caused pile—fly ash system of weakening, in peak load reaches level under the critical state displacement curve showed a trend of the rapid growth of nonlinear, cyclic cumulative failure occurs, and the cyclic load limit state is reached, which affects the service performance of the whole structure.

Model Test Study of Offshore Wind Turbine Foundation under the Combined Action of Wind Wave and Current

The wind turbine system in the offshore area will be subjected to the combined action of complex marine environment dynamic loads. At present, there is a certain advantage to using traditional mechanical devices to simulate marine environmental loads. In this study, the self-developed complex dynamic load test loading system is adopted to carry out a series of model tests for pile foundations. The theoretical calculation results of wind, wave and current load are applied to the wind turbine system, and the responses of the pile and soil are analyzed according to the actual model test. The main conclusions are as follows: the development of pile displacement is basically linear with the logarithm of cycle times, and pile–soil interaction is directly affected by the form of load, the results of dynamic response obtained in this test are closer to that under the actual marine environmental load.

Experimental and numerical study on the static lateral performance of monopile and hybrid pile foundation

Considering the limitations of conventional monopiles in supporting the new generation of offshore wind turbines (OWTs), the idea of hybrid pile foundation has been proposed and studied in recent years. In this paper, static lateral load tests are conducted on model piles and hybrid pile foundations in saturated sand. The influence of pile stiffness and hybrid foundation type on the lateral response is analyzed. Three-dimensional (3D) coupled discrete continuum modelling is further performed to reveal the interaction mechanism between different pile foundations and the surrounding soil. Experimental results indicate that the lateral capacity of the hybrid pile foundation can be notably improved compared with that of the monopile foundation, especially at small pile displacement. And the lateral load response of the hybrid pile foundation is comparable to that of the monopile at the ultimate limit state. From a numerical perspective, the load transfer mechanism of different pile foundations is studied by analyzing the displacement pattern of pile and soil foundation and the distribution trend of horizontal soil stress. It reveals that the existence of footing and bucket foundation could improve the efficiency of soil resistance mobilization at shallow depth. The experimental and numerical study is expected to provide some new perspectives on the understanding of the lateral bearing characteristics of hybrid pile foundations.

Method for Calculating Vertical Compression Bearing Capacity of the Static Drill Rooted Nodular Pile

The static drill rooted nodular (SDRN) pile is a new kind of composite pile foundation made by inserting a precast nodular pile into the cemented soil. Based on the tests and analysis on the mechanism characteristics of these two kinds of interfaces, which are between the pile and cemented soil, and between the cemented soil and soil, this paper proposes a calculation method for the ultimate vertical bearing capability of the SDRN pile considering two failure modes. When the precast pile and surrounding cemented soil fails as a whole, the diameter of the cemented soil pile is taken to calculate the ultimate shaft resistance, and the shaft resistance of the SDRN pile is about 1.05∼1.10 times that of the bored pile in the same soil layer. When the core precast pile fails in penetration mode, the diameter of the core pile is taken. The pile shaft resistance takes that of displacement piles in the same soil layer. The lower nodular pile shaft resistance should consider the squeezing effect of nodular joints. Besides, the improvement of pile tip resistance due to the expanded cemented soil should also be taken into consideration. The result is the smaller value calculated according to these two failure modes. The ultimate bearing capacity of a SDRN pile calculated by the theoretical method is not only compared with the field test result, but also the simulation result of a 2D model pile built by PLAXIS finite element software. In addition, the finite element simulation is also confirmed to be an effective way to investigate the mechanism characteristics of SDRN piles more thoroughly.

Effect of Pile-Soil Relative Stiffness on Deformation Characteristics of the Laterally Loaded Pile

Laterally loaded piles are widely used in structural foundations under horizontal loads such as wave load, wind load, seismic load, and traffic load. Based on the complexity of pile-soil interaction, a test simulation of single pile through the indoor 1 g model test was conducted, in order to study the influence of different loading heights and relative stiffness of pile and soil on the bending moment, soil resistance, and horizontal displacement of pile. It is found that the shear modulus of soil from large to small is arranged as dry fine sand, dry coarse sand, saturated fine sand, and saturated coarse sand. The shear modulus of dry fine sand, dry coarse sand, and saturated fine sand are close under the same loading height and horizontal displacement of pile top, while the shear modulus of saturated coarse sand decreases sharply. Under the condition of water saturation, the particle size has a significant effect on the shear modulus of soil. The relative stiffness of pile soil is found to be the main influencing condition of pile horizontal displacement. Compared with the displacement and bending moment of the pile, the loading height has more influence on the soil resistance, and the main influence area is the soil resistance of the pile toe.

Installation and aging effects on the capacity of small displacement piles

Pile setup is not fully understood, despite its high potential for cost saving and risk mitigation in onshore and offshore constructions. Studies indicate that the pile installation process has important influence on initial pile capacity and the subsequent setup. However, only few studies considered a wide range of installation methods (e.g., jacking, vibratory pile driving) when quantifying both initial capacity and setup characteristics. This study presents data of 88 static tension load tests conducted on 44 small piles at 1, 2, 10, and 100 days after their installation by four different methods. Piles made from mild and stainless steel exhibit strongly divergent setup characteristics, being a result of their different resistance to corrosion. Additional factors governing setup are the number of shear cycles induced during pile installation and the elapsed time after end of driving. We suggest a new approach considering the setup as a multidimensional effect, enabling the prediction of the initial capacity of a pile and its temporal development for the tested boundary conditions. This study provides a significant contribution to the understanding of the mechanisms governing setup by combining existing conceptual models, as friction fatigue and stress re-equilibration, together with corrosion under a time perspective.

Behavior of isolated floating pile adjacent to deep excavation reinforced by dual-row batter pile wall

The construction of modern city consists of many underground facilities, and one major concern is how to construct them safely and efficiently. Thus, the excavation-induced pile response needs to be evaluated. Dual-row batter pile wall (DRBPW) exhibits better performance than traditional dual-row vertical pile wall (DRVPW) in foundation pit engineering. However, the study of single pile subjected to excavation-induced soil movement behind DRVPW is rather limited, needless to say that of the DRBPW. An explicit finite difference method (FDM) was utilized to obtain the responses of isolated floating single pile (IFSP) near deep excavations braced by DRBPW. The responses of IFSP in the vicinity of foundation pit reinforced by DRBPW were compared to that of the DRVPW. The pile length, distance of pile from wall, excavation depth, working load, and Young’s modulus of pile were considered in the parametric study. The conclusions were as follows: (1) The DRBPW can minimize the influence on the existing pile; thus, the induced lateral displacement and bending moment of pile retained by DRBPW are smaller than that of DRVPW. (2) The excavation depth, pile location, and pile length have significant influence on the responses of IFSP adjacent excavation, while the working load and Young’s modulus of pile have diminutive influence. (3) The influence zone induced by excavation can be divided into two areas. The primary influence zone is the severely affected area where the induced deformation and bending moment are remarkable. The secondary influence zone is the moderately affected area where the induced deformation and bending moment are mild. The primary influence zone is within twice of the excavation depth. The secondary influence zone is 2.0–3.0 times that of the excavation depth. (4) The pile toe of IFSP has considerable lateral displacement during excavation, and attentions should be paid to the whole pile shaft during construction.

Experimental study on evaluating the lateral load capacity of raker pile in sloping ground

ABSTRACT A lot of uncertainty is associated with the behavior of pile foundations on the sloping ground due to factors like soil – pile interface and vague evaluation of pile bearing capacity. These constraints have a considerable impact on the extensive implementation of deep foundation on sloping ground. Comprehensive research studies were carried out on laterally loaded vertical piles on horizontal ground whereas only a limited number of studies have been conducted on the behavior of the laterally loaded raker-pile system on sloping sites. Therefore, to address this knowledge gap, the current investigative research paper aimed to study the results of a series of static lateral load tests were conducted in the laboratory on a single aluminium model raker pile embedded in loose sandy soil on 1V: 2H sloping ground. The loading directions were varied considering either forward (close to the slope) or reverse (away from the slope) loading for all pile positions. The influence of the sloping ground was quantified by measuring the pile response for horizontal ground conditions. It was observed that there is a significant increase in the displacement of the pile for the sloping ground surface compared to the horizontal ground. With an increase in the edge distance from the slope crest towards the embankment, a reduction in the pile displacement was observed. The optimum distance from the slope crest towards the embankment where the effect of slope becomes nullified under both forward and reverse lateral loads was determined as 10D (D – Diameter of the pile). From the obtained results, it was evident that in the case of the level ground and sloping ground with forward loading, the negative raker piles offer more resistance to lateral loads than vertical piles. In contrast, the positive raker piles endure the least lateral load with increasing inclination angle.

Vertical vibration of end-bearing single piles in poroelastic soil considering three-dimensional soil and pile wave effects

This paper presents an analytical solution developed to describe the dynamic interaction between a single end-bearing pile subjected to a dynamic axial load on its head, and its surrounding poroelastic soil. The main feature of the solution is that both the two-phase soil and the pile are treated as three-dimensional continua. This allows capturing the propagation of compressional and shear waves in three dimensions, and their effect on pile response. The soil surrounding the pile is treated as porous medium and its response is described with Biot’s poroelastic theory, while the pile is treated as linear elastic solid, considering explicitly both vertical and radial pile displacements. The solution yields expressions for the displacement and velocity admittance at the pile head in the frequency domain, and allows computing pile head velocity time histories. These are applied to study the effects of wave propagation in three dimensions on pile response in the frequency- and in the time-domain, and identify the conditions under which these effects may be important for the analysis of piles in practice.

Effect of groundwater on the displacements of axially loaded pile in clayey soil

Abstract The displacement of a loaded pile could be vertical (axial) or horizontal (lateral); these displacements are sensitive to groundwater presence within the soil mass. This paper presents a theoretical study to investigate vertical and horizontal displacement of piles embedded in a clayey soil for different levels of groundwater under the ground surface. The study was performed using the commercial finite element package PLAXIS-3D. Three diameters of the concrete piles were considered: 0.5, 0.75 and 1 m, and were subjected to 1,000 kN axial load. The effect of 0, 5, 10, 15 and 20 m groundwater along the 20 m pile in length from the ground surface on the vertical and horizontal displacements was investigated. The results indicated that the vertical and horizontal displacements increase when the ground water level increases towards the base of pile. Also, there is a significant increase in the horizontal displacement up to 15 m of groundwater level from ground surface and decreased at levels from 15 to 20 m.

Experimental simulation study on dynamic response of offshore wind power pile foundation under complex marine loadings

Offshore wind power structures are subjected to complex dynamic loads in marine environment during their service. At present, the real sea conditions can be simulated to the maximum extent by the mixed test technology of boundary layer wind tunnels, wave pools and shaking tables. However, due to the high cost of test and the lack of a complete and mature combined simulation laboratory which can be operated for wind, wave and seismic loads, it is difficult to carry out such joint tests. It is advantageous to use self-developed mechanical devices to simulate marine environmental loads within the controllable errors and which is in simple operation. A series of dynamic model tests were carried out on saturated sand foundation in order to explore the feasibility of studying dynamic response of offshore wind power pile foundations through simulating marine environmental loads by simplified methods. Based on Stokes second-order wave theory and harmonic superposition method, the time history of wind, wave and current load is derived and programmed, then the wind, wave and current load on offshore fan model structure is simulated by using self-developed complex dynamic loading system. Finally, the dynamic response of single pile foundation in saturated sand under complex load is analyzed according to the test results. The test results show that the load displacement curve of single pile foundation in saturated sand is of work hardening type. The maximum pile bending moment at the peak of dynamic load increases with the increase of loading times, but the cumulative effect of bending moment caused by the change of load amplitude should be considered. The dynamic load in marine environment will cause the increase of pore pressure around the pile, but the increase of pore pressure on loading side is not obvious in comparison to that on the opposite side. The displacement change of pile body is basically in accordance with the fluctuation trend of test load and increases with load. The cumulative rate of displacement of single pile decreases with the increase of number of cycles under the long-term cyclic wind wave load. In this study, the method combining theoretical calculation of wind, wave and current load with model test of complex loading system can consider the characteristics of dynamic loads of marine environment more accurately, compared with the empirically determined cyclic load waveforms in conventional tests, the obtained response law is more in accord with actual sea conditions.

Deformation Analysis and Prediction of Foundation Pit in Soil-Rock Composite Stratum

The deformation prediction of foundation pit is still an open issue in geotechnique engineering. This paper focuses on a new deformation prediction method of foundation pit in soil-rock composite stratum in Nanjing area. To do so, the field monitoring deformation data of deep foundation pit adjacent to the railway in a soil-rock combined stratum is firstly analyzed. Based on these field data, the characteristics of horizontal displacement and surface settlement of rock-socketed support pile, as well as its relationship with Earth excavation are discussed. Results show that the average value of maximum horizontal displacement of support pile in zone with shallow rock depth (soil layer >15 m) is relatively large, which is 3.5 times of that with shallow soil depth (10–12 m into moderately-weathered mudstone). The depth of maximum horizontal displacement is obviously linearly related to the thickness of soil layer (H), while the surface settlement does not change with the increase of soil/rock layer thickness ratio. Utilizing the relationship between the maximum water level displacement and excavation depth, a new Gaussian-type empirical formulation is established to predict horizontal deformation of soil-rock composite stratum with rock-socketed support pile. By comparison with two other methods, it is found that the improved Gaussian curve is in good agreement with the measured horizontal displacement curve. This indicates that the new method can provide a valid reference for the design and construction of foundation pit with rock-socketed support pile in Nanjing area.

A high-cycle accumulation model for clay and its application to monopile foundations

A high-cycle accumulation (HCA) model predicting the accumulation of permanent strain or excess pore water pressure in clay under a large number of load cycles is presented. Data from an extensive laboratory testing program on kaolin under undrained cyclic loading has been analysed for that purpose. The influence of strain amplitude, void ratio, stress ratio, overconsolidation ratio and loading frequency on the accumulation rates is considered in the constitutive equations of the HCA model. The proposed model is validated first by the simulation of element tests. Subsequently, its application to offshore wind turbine foundations under long-term lateral cyclic loading is presented by the back-analysis of a centrifuge test on a monopile in soft clay. The results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. It is concluded that the proposed model is feasible to describe the long-term behaviour of clay subjected to high-cyclic loading.

Evaluation of passive pile analysis methods using three-dimensional finite element analysis

ABSTRACT Piles in soft soil supporting bridge abutments are often exposed to passive loading induced by adjacent bridge approach embankment. Several methods for analysis of passive piles have been developed, but the international design specifications do not recommend a specific method for the analysis of passive piles. Therefore, the applicability of existing empirical and analytical analysis (conventional) methods is examined by comparing their outputs with those of a validated finite element model (FEM) at various adjacent embankment stress levels, and construction times, soft clay thicknesses, and pile spacing to diameter ratios. Outputs of both conventional methods and FEM show that increasing the embankment stress, thickness of soft clay layer, and pile spacing to diameter ratio results in an increase in the lateral pile displacement, maximum bending moment, and lateral pressure, and vice-versa on increasing embankment construction time. The outputs of the conventional analysis methods are compared to the FEM outputs and are underestimated except for few cases. The conventional analysis methods may yield better predictions at pile diameter-to-spacing ratio equals 3–4 for a soil preloaded prior to pile construction to a degree of consolidation greater than 50%.

Stability and load-displacement behaviour of axially cyclic loaded displacement piles in sands

Uncertainties regarding the axial cyclic behaviour of piles driven into sands led to an extended programme of calibration chamber instrumented pile experiments. Broad trends are identified and interpreted with reference to normalised cyclic loading parameters Qcyclic/QT, Qmean/QT, and N. Cyclic damage is shown to be related to changes in the radial effective stress regime close to the shaft. While stable loading leads to little or no change as cycling continues in the sand masses’ effective stress regime, high-level cyclic loading can affect stresses far out into the sand mass. The ratio of the chamber diameter to pile diameter of the test system has a significant impact on outcomes. Piles installed in loose, fine sand are far more susceptible to cyclic loading than those installed in denser, coarser sand. Little or no change in pile stiffness was seen in tests that remained within the stable cyclic region, even over 10 000 or more cycles. Unstable tests lost their stiffness rapidly and metastable cases showed intermediate behaviours. The permanent deflections developed under cycling depend on the combined influence of Qcyclic/QT, Qmean/QT, and N. While model tests provide many valuable insights into the behaviour of piles driven into sand, they are unable to capture some key features observed in the field.

Kinematic response of single vertical and batter piles to bidirectional ground motions in liquefiable soil

Kinematic responses of single fixed head vertical and batter piles in liquefiable soil under bidirectional ground motions have been studied with fully-coupled three-dimensional nonlinear dynamic analyses. Pressure dependent multi-yield constitutive model has been adopted for modeling the liquefiable sand behavior. The variable permeability of saturated sand during the process of liquefaction process has also been considered. The analyses are carried out for combinations of bidirectional earthquake loading conditions. For this, combination of longitudinal and transverse ground motions as well as combination of longitudinal and vertical motions are considered. The responses of the soil-pile systems under liquefying ground conditions, subjected to these bidirectional ground motions, are compared with the unidirectional loading conditions. Further, the effect of sloping ground on the response of the piles under bidirectional ground motions is also investigated. The developed sectional forces in both vertical and batter piles are lesser under bidirectional motions in comparison to unidirectional ground motion in both level and sloping grounds. However, the pile displacement is more in case of sloping ground under bidirectional ground motions comparing to unidirectional motion.

Experimental Investigation on the Vertical Bearing Characteristics of Jacked Piles in Saturated Silt Foundations under Excavation

A model test system for vertical bearing characteristics of the jacked piles in saturated soil foundations under excavation has been introduced. The system device comprises a soil pressure loading system, a model pile loading system, a soil vacuum saturation system, a model box, a model pile, and a control and data acquisition system. The soil vacuum saturation system designed for the model box of this test device can ensure that the saturated soil in the model box can reach a higher degree of saturation. Loading and unloading were conducted on the soil sample in the model box through the soil pressure loading system to simulate the soil excavation so that the soil sample and that in the field have the same stress state and history. The soil consolidation pressure, pile jacking pressure, pile tip force, soil consolidation settlement, and pile displacement at the top were collected and monitored in real time through the control and data acquisition system. This device is used to conduct an experimental study on the bearing characteristics of the jacked piles in saturated silt foundations under excavation. The results indicate that the static load test increases the residual pressure on the tip of the jacked pile while also increasing soil stiffness at pile tip and ultimate tip resistance, thereby increasing the pile top stiffness and ultimate load-carrying capacity. However, when the jacked pile is left undisturbed for the same time, the static load test on the jacked pile does not affect the pile skin friction resistance. There is a better linear relationship between the pile skin friction resistance and the undrained shear strength of the soil under the corresponding stress path during the static load test of the normally consolidated soil and the jacked pile after overburden pressure unloading. There is a good linear relationship between the ultimate resistance and the undrained shear strength of the soil under the corresponding stress path in pile sinking, normally consolidated soil, and during the static load test on jacked pile after unloading.

Shaking table test for seismic optimization of soil slope reinforced by new EPS pile under earthquake

To explore the optimal seismic performance of new EPS pile, we carried out a series of shaking table test by comparing different pile types. We measured and obtained the seismic data with various attributes, such as the characteristic image of different probability horizontal seismic action, acceleration and dynamic soil pressure. By analyzing the time-domain characteristics of multi-attribute data such as deformation characteristics and acceleration, we revealed the instability mode of the slope model and the regional response characteristics of particle spatial position. Based on the Fast Fourier Transform (FFT) and Statistical Probability Sperm Matrix (SPSM), we proposed the damage level correlation between the spectral characteristics of acceleration and dynamic soil pressure. We obtained the relationship between the variation of the frequency and specific period between acceleration and dynamic soil pressure at different seismic stages through in-depth study, and then calculated the regional differences of spectrum displacement (Sd) by using Seism Signal. In the frequency domain of acceleration and dynamic soil pressure signals, the predominant frequencies were mostly concentrated in 0.5–8 Hz. Under high seismic acceleration, the amplitude frequency of acceleration spectrum of conventional pile and EPS pile was both 1.51 Hz, and the dominant frequency of dynamic soil pressure was significantly different. There was a positive correlation between seismic acceleration and dynamic soil pressure. The shift of frequency profile and main frequency band of EPS pile was mainly caused by the propagation stage after the acceleration main shock. Under high seismic acceleration, the deformation of EPS pile and conventional pile occurred to some extent. EPS plate was used as the damping layer to buffer and dissipated the deformation of the slope under earthquake, and its effect was linked to the seismic data attributes. The spectral displacement of EPS pile was reduced as a whole was higher than that of conventional pile. The slip surface of pile body was sensitive to earthquake, and it was easy to become the weak seismic link of the EPS pile. These results are helpful for us to provide a theoretical basis for improving the reliability optimization design of dynamic parameters of the pile structure.

The effect of model scale, acceleration history, and soil condition on closed-ended pipe pile response under coupled static-dynamic loads

This paper analyzes the effect of scaling-up model and acceleration history on seismic response of closed-ended pipe pile using a finite element modeling approach and the findings of 1g shaking table tests of a pile embedded in dry and saturated soils. A number of scaling laws were used to create the numerical modeling according to the data obtained from 1g shake table tests performed in the laboratory. The current study found that the behaviors of the scaled models, in general have similar trends. From numerical modeling on both the dry and saturated sands, the normalized lateral displacement, bending moment, and vertical displacement of piles with scale factors of 2 and 35 are less than those of the pile with a scale factor of 1 and the shaking table test. In general, the pile deformation factor was higher in saturated sand models than the dry sand models. Liquefaction ratios were increased by increasing the seismic intensity; hence the maximum liquefaction ratio was observed with the model of scale 1 under the effect of the Kobe earthquake (0.82g). In another full-scale model, the liquefaction ratio decreased significantly; i.e., it was decreased from 1.64% (λ=1) to 1.04% (λ=35) in the same mentioned model. Pile frictional resistance was numerically investigated and the overall results were compared with previous studies in the literature. In general, the frictional resistance at the pile tip was slightly higher than the frictional resistance around the pile body, and the frictional resistance factor on the ground surface of dry soil models was slightly higher than those of saturated soil models.