Piles In Dense Sand Research Articles

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 Pressure Distribution under Screw and Straight Pile in Dense Sand

Experimental and Numerical Study on Pressure Distribution under Screw and Straight Pile in Dense Sand

Numerical study on the installation effect of a jacked pile in sands on the pile vertical bearing capacities

The installation effect of a jacked pile in silica sand is investigated numerically. A simplified state-dependent dilatancy model is used to model the sand behavior and the sand grain crushing effect is considered by modifying the critical state line at large confining pressures. The Arbitrary Lagrangian-Eulerian (ALE) technique is adopted to model the pile penetration and the load-displacement behavior at the operational loading stage is simulated using standard finite element method with the initial states being the equilibrium of the pile-jacking-disturbed soil stress and void ratio fields and a free pile head. The numerical procedure has been verified against some calibration chamber tests and centrifuge tests. Simulations of wished-in-place piles are performed for the quantitative study of the installation effect. The results show that the capacity ratios between the jacked and wished-in-place piles become higher for long piles in dense sand. Linear fittings have been applied to obtain the capacity ratios as functions of the relative density and the penetration length-to-diameter ratio, which can be used for a quick estimation of the bearing capacity difference between jacked and wished-in-place piles.

P-Y curves for laterally loaded single piles: Numerical validation

Pile foundations are widely used in marine and coastal engineering structures. The correct analysis method must be used to ensure the safety of piled systems used in marine and coastal structures. Despite several methods available in the literature, the numerical method is increasingly applied for understanding the loading mechanism of pile-soil interaction under vertical, lateral, or seismic loadings. The present study focuses on the numerical validation of centrifugal test results of the single pile in dense sand under lateral loading. An extensive parametric study is carried out to validate numerical models due to the lack of experimental tests such as shear or triaxial tests. In the numerical model, the soil is represented by a kinematic hardening model, which is simple to calibrate in finite element analysis, whereas pile is modeled as an elastic material. The p-y family of the curve is back-calculated for a single pile and an algorithm is generated. Two interface models between soil and pile, namely full contact and frictional slip contact, are investigated to represent the behavior under horizontal loading. Then, the analyses are extended to vertical loading to assess the influence of interface models.

Evaluation of Seismic Soil–Structure Interaction of Full-Scale Grouped Helical Piles in Dense Sand

Abstract A full-scale shake table testing program was performed with two helical pile groups supporting model structures to better understand the dynamic properties of a soil–pile-group–structure s...

Lateral bearing behaviour of vibro‐ and impact‐driven large‐diameter piles in dense sand

AbstractMonopiles are the preferred foundation solution for offshore wind turbines in sandy soils below shallow and moderate water depths. The piles are commonly installed using impact driving. A severe disadvantage of this installation method is that high noise levels occur in the water, which are a risk to animals living in the sea. Approval authorities are known to impose statutory requirements to mitigate this risk, placing a financial burden on installation. Vibratory driving is an alternative installation method that reduces noise emission levels significantly. However, the effect of vibro‐driving on the bearing behaviour of piles under lateral loading is largely unknown. Full‐scale load tests were conducted in predominantly dense, non‐cohesive, saturated soil to investigate the differences between impact‐driven piles and vibrated piles regarding their lateral bedding behaviour. CPTs and pile head load‐displacement curves were recorded and evaluated. In general, it was determined that the bearing behaviour of vibro‐driven piles is heavily dependent on the parameters of the installation process. For the installation parameters used in the test campaign, two vibro‐driven piles showed a weaker bedding reaction in comparison to the impact‐driven piles, although one vibrated pile installed with unintentionally different parameters showed an only slightly weaker behaviour under primary loading and even increased unloading and reloading stiffness. Furthermore, it was observed that an indication regarding the differences in the bedding resistance can be obtained via CPT measurements before and after installation, since the installation procedure considerably affects the relative density of the soil around the pile.

Dynamic Response of a Single Pile Embedded in Sand Including the Effect of Resonance

In this paper, responses of a single pile embedded in sand soil (loose and dense) under dynamic loading (sinusoidal dynamic vibrations of 0.1 g to 0.5 g) have been investigated by two-dimensional analysis using the finite element method (FEM). Viscous (dashpot) boundaries have been used for taking the boundary effects of far-field into account. The applicability and accuracy of site responses of two-dimensional analysis due to the FEM modelling have been well verified with one-dimensional site responses. The results indicate that the relative density of sand (loose, dense) becomes prominent for the displacements of the pile, specifically under the frequency effects of resonance. While the pile in loose sand causes the displacements of 0.1 m to 0.5 m, the pile in dense sand leads to the displacements of 0.05 m to 0.25 m, proportionally with the dynamic loads from 0.1 g to 0.5 g. Moreover, the displacements reach their peak value at the frequency ratio of the resonance case. Viscous boundaries are found sufficient for modelling excessive displacements due to dynamic loading. However, the displacements reveal that high vibrations (> 0.1 g for loose sand, > 0.2 g for dense sand) influencing the pile deformations are critical for the issues of settlements. This is more significant for the resonance case in order for ensuring sufficient design. Consequently, the findings from the study are promising good contributions for pile design under the dynamic effect.

Drained response of rigid piles in sand under an inclined tensile load

The response of rigid piles in sand to an inclined tensile load is poorly documented and understood, particularly when the load is cyclic. This is becoming relevant for floating marine renewable energy devices such as wave energy converters and floating wind turbines. This paper considers centrifuge data for rigid piles in dense sand subjected to drained monotonic and cyclic loading at various inclinations. The data strongly advocate (in dense sand) the avoidance of load inclinations higher than about 60° (to the horizontal) as cyclic loading significantly deteriorates pile capacity, whereas at lower (flatter) load inclinations, there are potential benefits from cyclic densification that improve pile capacity.

Assessment of p-y Behaviors of a Cyclic Laterally Loaded Pile in Saturated Dense Silty Sand

Assessment of p-y Behaviors of a Cyclic Laterally Loaded Pile in Saturated Dense Silty Sand

The Recycling Torque of a Single-Plate Helical Pile for Offshore Wind Turbines in Dense Sand

The helical piles have been being treated as a kind of novel foundation for offshore wind turbines recently, due their fast installation, high uplift capacity, convenience for recycling, and other advantages. The recycling of the helical pile especially will reduce the cost significantly and protect the environment as much as possible. However, the research for this area is basically in infancy and there is no reference for predicting the recycling torque of a helical pile in sand. In order to predict the recycling torque of single-plate helical piles in dense sand: a theoretical model, which was inspired by the way to predict the installation torque of single-plate helical pile in sand, was developed, and a series of single gravity model tests were conducted to verify that theoretical model. The theoretical model can predict the recycling torque of single-plate helical pile considering the influences of the size of helix and the vertical force on the shaft. This model fills in the blank of predicting the recycling torque of a single-plate helical pile in sand and it is also useful guidance for the choice of suitable recycling equipment.

Enhancement of The Behaviour of Laterally Loaded Vertical Piles Embedded in Clayey Soil

One of the most important problems is the construction on a soft clay soil, which extends over many areas in Egypt, Construction on a soft clay soil requires the use of deep foundations. In most of the cases the pile lateral capacity isn't satisfied due to the upper soft clay layers. Thus, there is a need to enhance the lateral load behavior of the pile. This paper is to study the enhancement of the lateral behavior of piles by replacing the upper layers of soft clay with dense sand. A series of laboratory tests were conducted on a single pile in soft clay soil. The upper clay layer around the pile was removed and replaced with compacted dense sand and the tests were repeated. The model pile used in this study was made of smooth hollow steel pipe. The outer diameter and wall thickness were 21 and 1.8 mm, respectively. Results indicated that the improvement of laterally loaded pile behavior was found to be strongly dependent on the replaced layer depth and replaced layer extension around the pile in dense sand. Results of experimental investigations were used to extract the lateral load-lateral displacement (P-Δ) curves.

Shaft capacity of pre-bored grouted planted nodular pile under various overburden pressures in dense sand

This paper presents the results of a series of model tests performed to study the shaft capacity of pre-bored grouted planted nodular (PGPN) pile in dense sand. The influence of the vertical overburden pressure on the shaft capacity of the PGPN pile is also investigated based on the test results. The test piles were equipped with strain gauges to measure the axial loads during the loading process, moreover, a foam plate was buried beneath pile tip to eliminate the influence of tip resistance on the shaft capacity. Some conclusions can be drawn based on the test results: the peak skin friction of PGPN pile increases with the increase of vertical overburden pressure applied on the foundation soil, while the rate of increase decreases with the increasing overburden pressure; the surface of the pile–soil interface of PGPN pile is relatively rough, and significant dilatant increase in lateral stress occurs during the loading process.

Effect of loading direction on the shaft resistance of jacked piles in dense sand

The design of piles subjected to tensile loading is usually done by applying a correction factor on the shaft resistance calculated for compressive loading, but experimental data on what this correction factor should be are limited. This paper presents the results of a series of tensile–compressive (TC) and compressive–tensile (CT) static loading tests performed on instrumented model piles (with three different values of surface roughness) jacked into dense sand samples prepared in a half-cylindrical calibration chamber with digital image correlation (DIC) capability. Digital images of the model pile and sand were taken during loading of the pile in each test and processed using the DIC technique to obtain the soil displacement and strain fields. Results from local sensors showed that the ratio of the tensile-to-compressive shaft resistance of jacked piles is always less than one and depends on both the sequence of loading (CT or TC) and the pile surface roughness. The lower shaft resistance measured in tensile loading is due to the rotation of principal strains that occurs upon reversal of loading direction. Localisation of shear strains occurred within a thin band of sand around the pile shaft.

Model tests comparing the behavior of pre-bored grouted planted piles and a wished-in-place concrete pile in dense sand

The compressive bearing capacity of wished-in-place (WIP) concrete piles and pre-bored grouted planted (PGP) piles in dense sand was investigated by means of model tests. In total, three model piles were tested. The load–displacement response, axial force and tip resistance of each model pile were measured in the static load test process. Several conclusions can be drawn from the model test results: the pre-bored grouted planted nodular (PGPN) pile and the pre-bored grouted planted pipe (PGPP) pile have ultimate skin friction 1.23–1.36 times and 1.34–1.46 times greater than the ultimate skin friction of the wished-in-place (WIP) pile, respectively. The tip bearing capacity of the PGP pile is similar to the tip bearing capacity of the WIP pile, and the hyperbolic model of normalized tip resistance (qb/qc) and normalized tip displacement (Sb/D) can represent the tip load–displacement response of the WIP and PGP piles well.

Lateral Response of a Single Pile under Combined Axial and Lateral Cyclic Loading in Sandy Soil

According to practical situation, there have been limited investigations on the response of piles subjected to combined loadings especially when subjected to cyclic lateral loads. Those few studies led to contradictory results with regard to the effects of vertical loads on the lateral response of piles. Therefore, a series of experimental investigation into piles in dense sand subjected to combination of static vertical and cyclic lateral loading were conducted with instrumented model piles. The effect of the slenderness ratio (L/D) was also considered in this study (i.e. L/D= 25 and 40). In addition, a variety of two-way cyclic lateral loading conditions were applied to model piles using a mechanical loading system. One hundred cycles were used in each test to represent environmental loading such as offshore structures. It was found that under combined vertical and cyclic lateral loads the lateral displacement of piles decreased with an increase in vertical load whereas it causes large vertical displacements at all slenderness ratios. In addition, for all loading conditions the lateral, vertical (settlement and upward) displacements and bending moments increased as either the magnitude of cyclic load or the number of cycles increases.

An Innovative Experimental Setup for Characterizing Friction Fatigue during Cyclic Jacking of Piles in Dense Sand

AbstractIn this study, an innovative experimental setup for model pile tests was developed to characterize friction fatigue in sand during cyclic jacking. In the experimental setup, a high-performance precision electric linear actuator was used to control jacking of the model piles. P-wave tomographic imaging was used to characterize the associated changes in the distribution of the P-wave velocities in the soil, and tactile pressure sensors were utilized to monitor related variations in stresses in the soil surrounding the pile. Measurements obtained from the experiments allow us to explore the behavior of fiction fatigue from a different perspective, especially from the viewpoint of stress changes in the soil surrounding the pile. It was found that for a soil element surrounding the pile in a jacking cycle, the maximum values of the stationary radial and hoop stresses and the ultimate radial and hoop stresses in that soil element are reached when the pile penetrates to nearly the same depth, which is therefore defined as the transition depth. For the soil elements at the same depth, such a transition depth increases with increasing distance from the pile centerline. When the pile base gradually penetrates through the transition depth, these stresses in the soil elements surrounding the pile will exceed the peak value, which in turn leads to a reduction in the ultimate unit shear resistance (τf), giving rise to friction fatigue. Based on these experimental findings, a simple model is also proposed to explain friction fatigue.

Shaft capacity of the pre-bored grouted planted pile in dense sand

The pre-bored grouted planted pile is a new type of composite pile foundation that consists of a precast concrete pile and the surrounding cemented soil. A series of shear tests were conducted in a specific shear test apparatus to investigate the shaft capacity of the different pile–soil interfaces. The test results show that the frictional capacity of the cemented soil–sand interface is controlled mainly by the sand properties, while the strength of the cemented soil slightly influences the interface properties by affecting the normalized roughness coefficient Rn. The frictional capacity of the concrete–sand interface is similar to the frictional capacity of the cemented soil–sand interface, and the existence of mud cake layer virtually hampers the frictional properties of the interface. The maximum skin friction of the concrete–cemented soil interface increases approximately linearly with the increasing cemented soil strength, and the value of the maximum skin friction is much larger than that of the cemented soil–sand interface of identical cemented soil strength, which demonstrates the integrity of the pre-bored grouted planted pile in the load transfer process.

Incremental filling ratio of pipe pile groups in sandy soil

Formation of a soil plug in an open-ended pile is a very important factor in determining the pile behavior both during driving and during static loading. The degree of soil plugging can be represented by the incremental filling ratio (IFR) which is defined as the change in the plug length to the change of the pile embedment length. The experimental tests carried out in this research contain 138 tests that are divided as follows: 36 tests for single pile, 36 tests for pile group (2x1), 36 tests for pile group (2x2) and 30 pile group (2x3). All tubular piles were tested using the poorly graded sand from the city of Karbala in Iraq. The sand was prepared at three different densities using a raining technique. Different parameters are considered such as method of installation, relative density, removal of soil plug with respect to length of plug and pile length to diameter ratio. The soil plug is removed using a new device which is manufactured to remove the soil column inside open pipe piles group installed using driving and pressing device. The principle of soil plug removal depends on suction of sand inside the pile. It was concluded that the incremental filling ratio (IFR) is changed with the changing of soil state and method of installation. For driven pipe pile group, the average IFR for piles in loose is 18% and 19.5% for L/D=12 and 15, respectively, while the average of IFR for driven piles in dense sand is 30% and 20% for L/D=12 and L/D=15 respectively. For pressed method of pile installation, the average IFR for group is zero for loose and medium sand and about 5% for dense sand. The group capacity increases with the increase of IFR. For driven pile with length of 450 mm, the average IFR % is about 30.3% in dense sand, 14% in medium and 18.3% for loose sand while when the length of pile is 300 mm, the percentage equals to 20%, 17% and 19.5%, respectively.

Optimization Technique to Determine the p-y Curves of Laterally Loaded Stiff Piles in Dense Sand

Abstract Lateral loading is often the governing design criteria for piles supporting offshore wind turbines and with the recent growth of this sector, the reliability of traditional design approaches is receiving renewed interest. To accurately assess the behavior of a laterally loaded pile requires a detailed understanding of the soil reaction that is mobilized as the lateral deflection of the pile occurs. Currently, the p-y curve method is widely adopted to model the response of laterally loaded piles. The limitations of existing p-y formulations are widely known, and there is acceptance that load tests on large-diameter stiff monopiles are urgently required to formulate appropriate design methods. However, interpretation of the data from instrumentation placed on stiff monopiles is not straightforward. This paper proposes an optimization technique to derive the soil reaction profile along the shaft of instrumented piles, from which the correlated p-y curves can then be obtained. The method considers force equilibrium, pile deflection, and additional boundary conditions. A set of fourth-order polynomial equations are assumed to model the soil reaction profile under each load step during a monotonic load test. By minimizing the difference between the measured and calculated bending moment and considering equilibrium of the shear forces acting on the pile, the soil reaction profile and the concentrated tip resistance can be obtained simultaneously. A stiff instrumented test pile installed in over-consolidated sand was load tested and the results were used to test the performance of the proposed method. The results are compared with other methods used in literature and practice. The method provides a consistent framework to derive p-y curves from measured strain data. The results of the field test and derived p-y curves confirmed that existing design methods do not accurately capture the lateral loading response of piles in dense sand.

Effect of Ground Mineralogy on Energy Pile Performance in Dense Sand

Geothermal energy piles have emerged as a cost effective and efficient solution for heating and cooling buildings through renewable energy. Although significant research effort has been dedicated to investigating the performance of these systems, the effect of ground mineralogy has received little attention. This study examines the likely performance of energy piles in dense sand with varying mineralogy. A 3D thermal discrete element model is used to determine the dry thermal conductivity of quartz, feldspar and mica rich sand. This is then used in a 2D finite element analysis to estimate the dissipation/extraction capacity of the soil surrounding a typical energy pile. A 35% increase in quartz content is predicted to result in 51% improvement in the thermal performance of a pile.