Large-diameter Piles Research Articles

Theoretical analysis of three-dimensional effect in pile integrity test

The one-dimensional (1D) rod model, which is used in several pile dynamics applications, has two main simplifying assumptions: only vertical reaction is considered and excitation on the pile top is treated as uniform. These two simplifications negatively affect its application in pile integrity tests, especially for large-diameter piles. To overcome these two limitations, a new non-uniform axisymmetric loading (NAL) theoretical model that considers bidirectional (vertical and radial) reactions of the pile body and the non-uniformity of the excitation on the pile top is proposed. Based on the developed model, displacement and velocity fields of an end-bearing pile embedded in homogeneous soil under non-uniform impact are solved theoretically. Analytical solutions are then verified by existing solutions and finite element results. Compared with 1D rod pile model, the NAL model can predict accurately the three-dimensional (3D) effect in the pile integrity test. Extensive parametric analysis is conducted using the present solutions to evaluate the 3D effect in the pile integrity test and provide practical suggestions to diminish the 3D effect in the actual test.

An Analytical Solution for Longitudinal Impedance of a Large-Diameter Floating Pile in Soil with Radial Heterogeneity and Viscous-Type Damping

An analytical model is presented for solving the longitudinal complex impedance of a large-diameter floating pile in viscoelastic surrounding soil with radial heterogeneity and viscous-type damping, taking the effect of three-dimensional wave propagation of soil and lateral inertia of the pile shaft into account. The corresponding analytical solution for longitudinal impedance is also derived and validated via comparisons with existing solutions. The influences of the pile length, Poisson’s ratio of the pile shaft and the viscous damping coefficient, as well as the degree and radius of disturbed surrounding soil, on the longitudinal impedance of the pile shaft are examined by performing parametric analyses. It is demonstrated that the proposed analytical model and solution are suitable for the longitudinal vibration problem of a large-diameter pile and radially inhomogeneous surrounding soil, especially when the pile slenderness is low. In addition, the present solution can be easily degenerated to describe the longitudinal vibration problem relating to a large-diameter floating pile in radially homogenous soil or a pile with fixed-end supports.

Quantifying the influence of pile diameter on the load transfer curves of laterally loaded monopile in sand

Although the load transfer curves (i.e., p-y curves) recommended by the current industry standards are regarded as questionable for the recently emerging large diameter monopile, the influence of pile diameter and bending stiffness on the p-y curves in sand has not been systematically quantified. Nor have the underlying mechanisms of the diameter dependent p-y curves been well understood. This study presents a series of well calibrated three-dimensional finite-element (FE) analyses, aiming to quantify p-y curves of laterally loaded piles with different pile diameters and bending stiffness in sand, and to reveal the underlying mechanisms. It is found that the p-y curves in the API [6] code, which are valid for piles with a small diameter (D = 1 m), overestimate the initial stiffness while underestimates the soil resistance of a large-diameter pile (D = 5 m) by more than 90%. The numerical analyses further reveal that the modification of the p-y curves with the increasing pile diameter is mainly associated with the altered soil deformation mechanisms around the increasingly stiff pile. On the other hand, the influences of the skin friction, base shear and base moment of the large-diameter pile (with D up to 5 m) on the p-y curves are almost negligible. New p-y curves considering the effect of failure mechanism of large diameter monopile in dense sand is proposed, which are shown to yield better predictions for large-diameter piles than the existing p-y curves.

A new large step-tapered hollow pile and its bearing capacity

This paper introduces a new large step-tapered hollow (STH) pile used in a karst area and its construction method. To reveal the advantages of this pile type, a 15 m dia. STH pile in Ji'an Shenzhen Bridge was simulated using Flac3D software. The vertical bearing capacity was assessed by considering the influences of the width and number of the variable cross-sections and the soil characteristics around the pile. In addition, new large STH piles of two different forms were assessed to expand the practical application of such piles. The results showed that, for a large-diameter pile, the concrete utilisation rate and the vertical bearing capacity of the pile were improved by the design of hollow and variable cross-sections. The optimal range of the taper angle for the large STH pile was found to be 2·68–5·36° and the optimal number of variable cross-sections was found to be between two and four. The bearing capacity increased with an increase in the soil shear strength parameters and the pile was deemed suitable for stiff strata. The results of this work could facilitate design practice for large STH piles.

Modeling of Large Diameter Piles in Soil Formations Including Soft Clay

In Egypt, large diameter piles are used in some sites with diameters exceeding 2 m. In some cases, these piles carry foundations of heavy structures and/or large vertical and lateral loads. The analysis and design methodologies of large diameter piles are mainly controlled by the relatively smaller diameter piles, usually ranging between 60 and 120 cm. However, there is a special need for the analysis and design of larger diameter piles (i.e., larger than 120 cm) to assess their actual load carrying capacities. This paper presents numerical modeling of end bearing piles constructed in thick layer of soft to very soft clay underlain by a dense sand layer, typical to large zones in Northern and North Eastern zones in Egypt. The finite element analysis software ADINA (2018) [2] is used to simulate the behavior of the large diameter bored piles. Results showed that increasing the pile diameter cause a corresponding increase in pile capacity. It is also noticed that increasing pile embedded length in the end bearing sand layer has an enormous effect on pile capacity especially for larger diameter piles.

The concept and implementation of an energy retaining wall of large diameter piles

Performance and success of energy geostructures systems are already facts proven by research and practice. The number of implementations is in constant grow and due to their advantages, such systems have started to be implemented in a variety of structural elements. Among the various types, energy piles are the most common type of energy geostructures. However, most of the existing research, experimental sites and case studies refer to energy piles as a foundation element. This paper presents the concept and implementation steps of a different type of energy piles system which is a retaining wall of piles built in Cluj-Napoca, Romania. The paper is based on a real project case study, where large diameter piles are used as retaining wall for an urban excavation on a steep slope with high slope failure potential. The piles from the retaining system have been energy equipped in order to be used as an energy exchange element with the ground for heating and cooling demand of 3 new residential buildings from the same site. The paper will present the concept of an urban energy retaining wall and implementation stages of the project.

The advanced p-y method for analyzing the behaviour of large-diameter monopiles supporting offshore wind turbines

The analyses of monopile foundations have been heavily based on the p-y response curves (to represent lateral soil resistances) published by API RP 2GEO (2011) and DNV (2013), which are proven reliable and applicable for piles with smaller diameters that were normally used for jacket structures in the offshore industry. However, concerns have been raised about the validity of semi-empirical p-y criteria for large-diameter piles. Wind turbine monopiles have a significantly larger diameter and smaller length to diameter ratio than typical piles used for offshore structures. The ratio of the length to the diameter for a monopile typically is also significantly smaller than those used in the API load tests. Therefore, the response of a monopile may be more like a rigid rotation, with components of resistance mobilized at the tip and axially along the sides as it rotates. This behaviour is in contrast to long slender piles that respond to lateral loading in bending rather than rotation. The objective of this paper is to analyze the factors that may contribute to the apparent conservatism in the current design practice for large-diameter monopile foundations and to provide improved solutions on how to analyze and design the large-diameter monopiles for offshore wind turbine using the p-y method.

A Research on Access of Load Carrying Capacity of Large Diameter Piles

The evaluation of load carrying capacity of piles needs the geotechnical properties, penetration tests, the nature of the subsoil both around and beneath the proposed pile, adequate description of rock to convey its physical behavior on borings, dead loads, live loads dimensions of the piles (length and diameter of pile). To compare the length and diameter response of bored cast in situ piles, the data required is obtained from the site of project name Four Laning Project of Nagpur-Saoner-Betul Section of NH-69. The subsoil profile of site shows the clayey and silty clayey soils at the top to the considerable depth underlying highly weathered sandstone. The water table is observed from 4.5 m below the ground level. Here it is not possible to provide shallow, raft foundation as the soil strata mostly clayey and silty clayey soils which have very less safe load bearing capacity. Hence deep foundation proposed for the work. Sufficient number of borings taken in accordance with IS: 1892. Study is done by using all these geotechnical engineering properties at all bore holes locations, varying length and diameters of piles for evaluation of load carrying capacities as per IS:2911 (Part 2) and IRC:78. The load carrying capacity for different diameter of piles and for different length of piles goes on increasing with the increase in diameter. The contribution of end bearing resistance increases up to 170%, whereas contribution of frictional resistance increases up to 40%. Theoretical settlement for different diameters of piles for 25m length of pile has been computed. It has been observed that the theoretical settlement for 1.2 m diameter pile for 25 m length of pile is found to be more than actual settlement obtained from pile test for the same dimensions of the pile. Since theoretical settlement prediction is within in permissible limit and greater than the settlement obtained from the actual pile load test data, the load – settlement designed using excel can be used by the geotechnical engineers for prediction of the load and settlement calculations.

Influence of large-diameter pipe pile driving on surrounding marine soils and adjacent submarine pipelines

With the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing.

Comparative Analysis and Research of Different Ways to Deal with the Soft Soil Foundation

Taking an engineering example as background, the deformation and settlement of CFG pile and artificial bored pile composite foundation under the same geological condition are analyzed by using finite difference method. The simulation results show: the same formation and pile material and compaction process, the large diameter and deep manual bored pile foundation can significantly restrain the foundation drop, the analysis results have certain reference value for similar projects.

Prediction of Pile Capacity of Socketed Piles Using Different Approaches

This paper presents the analysis of formerly available pile load test data of different places in Mumbai region to estimate the ultimate load carrying capacity using different empirical methods. Conducting a load test is the best way to analyse the load settlement behaviour of rock-socketed pile. But because of support reaction and time limitation, the test can’t be conducted till failure of pile. The load settlement database of six pile load test are extrapolated using different empirical methods like De Beer’s method (1967), Chin-Kondner Extrapolation method (1970), Vander Veen’s method (1953), Decourt’s method (1999) and Shen method (1980). These methods determine the yield limit load and Decourt’s method is showing satisfactory result as compared to previous case studies. The relationship between ultimate load carrying capacity and different pile diameter can be used for estimation of ultimate capacity of large diameter piles which can’t be tested using field pile load test due to economical constraints. Safe load capacity of piles is calculated according to IS 14593. For further advancement of study, relationship between socket friction and pile diameter can be recognized and comparisons between static and dynamic safe load can be illustrated.

Scour Effects on the Lateral Behavior of a Large-Diameter Monopile in Soft Clay: Role of Stress History

Scouring of soil around large-diameter monopile will alter the stress history, and therefore the stiffness and strength of the soil at shallow depth, with important consequence to the lateral behavior of piles. The existing study is mainly focused on small-diameter piles under scouring, where the soil around a pile is analyzed with two simplified approaches: (I) simply removing the scour layers without changing the strength and stiffness of the remaining soils, or (II) solely considering the effects of stress history on the soil strength. This study aims to investigate and quantify the scour effect on the lateral behavior of monopile, based on an advanced hypoplastic model considering the influence of stress history on both soil stiffness and strength. It is revealed that ignorance about the stress history effect (due to scouring) underestimates the extent of the soil failure wedge around the monopile, while overestimates soil stiffness and strength. As a result, a large-diameter pile (diameter D = 5 m) in soft clay subjected to a souring depth of 0.5 D has experienced reductions in ultimate soil resistance and initial stiffness of the p-y curves by 40% and 26%, and thus an increase of pile head deflection by 49%. Due to the inadequacy to consider the stress history effects revealed above, the existing approach (I) has led to non-conservative estimation, while the approach (II) has resulted in an over-conservative prediction.

Comparative Concept Design Study of Laterally Loaded Monopiles

Offshore wind turbine generators (WTG) are commonly founded on single large diameter piles, named monopiles. These monopiles are subjected to significant lateral loads and thereby sizeable overturning bending moments mainly due to action of wind and wave forces; thus the critical geotechnical design situation for monopiles supporting WTGs is often related to lateral loading conditions. The Pile Soil Analysis (PISA) joint industry research project [1] has recently proposed a monopile design method which encompasses finite element (FE) calculations under a specific design framework. Soil reaction curves that are crucial for monopile design (i.e. lateral force and moment reactions along the shaft and at the base of the pile) are derived from FE calculations, subsequently calibrated and entered into a 1D model which is then used for design optimisation. This method is implemented within the PLAXIS MoDeTo (Monopile Design Tool) software. This paper presents results of a concept monopile design study under lateral monotonic loading with the use of the PLAXIS MoDeTo method.

Study on Calculation of Pile Sliding Interval of Large-Diameter Steel Pipe Piles on Offshore Platforms

In ocean engineering, pile sliding often occurs in the driving process of large-diameter pipe piles and will affect the engineering quality, so accurate pile sliding interval is necessary. According to the stress situation of steel pipe pile out of actual engineering, the causes of pile sliding are analysed. Using the static equilibrium equation, the mud depth at which the pipe pile may slip is calculated. The influence of pile siding friction was considered when calculating the second pile sliding, and the pile siding friction is divided into three influential areas. Using integrating method, the work done by pile resistance is calculated. Combined with the working principle and power principle, the energy transformation equation of the pipe pile in the process of sliding is obtained, and the sliding length and interval of the pile are calculated. A comparison between the measured results and the real case calculation was conducted using this new method. The comparison indicated that the total relative errors in pile sliding interval are 8% to 16%, and the new method has high accuracy. The results of the new method are in accord with the measured data, which can provide a reference for predicting the interval of pile sliding in the project.

Vertical bearing capacity of the pile foundation with restriction plate via centrifuge modelling

Pile foundation is one of the most commonly used foundations for offshore and coastal structures. This paper describes an innovative design for the pile foundation, which institutes an innovative strategy over traditional pile foundation to achieve higher axial bearing capacity. This is achieved by adding restriction plates inside the pile to help form the soil plug. A series of geotechnical centrifuge tests are carried out to evaluate the load bearing behaviors of traditional pile foundation and innovative pile foundation with different types of restriction plates. The pile diameter and shapes of the restriction plates on the soil plug behaviors and pile load carrying capacity are analyzed. The results show that the use of restriction plates could significantly increase the axial bearing capacity of large diameter pile foundations. For different pile diameters, the restriction plates with four smaller holes achieve better performance than those with one large hole of the same effective opening areas. A bearing capacity equation is obtained by normalizing the ultimate bearing capacity with the pile diameters for different restriction plates. This study demonstrates the promise of an innovative pile foundation with a restriction plate as an economic and technically feasible way to produce higher load-bearing capacity to support offshore and coastal structures.

Dynamic load test of full-scale pile for the construction and rehabilitation of bridges

Seven dynamic load tests were performed on six large diameter piles, installed near the Gumti river Bangladesh. The diameter of five cast in situ piles was 1.5 m, and that of the steel pile was 1 m. The steel pile was tested twice: under both drive and re-drive conditions. The pile lengths varied from 45 m to 71.8 m. The distribution of pile bearing resistance under static load were evaluated using the program DLTWAVE by signal matching. In addition, standard penetration tests were conducted in the vicinity of all the six piles. The results of dynamic load test were calibrated by comparing the static capacity obtained from static and dynamic load tests, conducted on two identical cast in place piles. Therefore, the skin frictional resistance and pile tip resistance are calculated using the conventional formulae of static analysis utilizing the developed correlation for the clay layers. The consistency of clay soil is observed to play an important role in the development of shaft resistance. For very stiff to hard clay, DLTWAVE indicates the development of shaft resistance smaller than that obtained from the formula (static analysis). Greater skin frictional resistance was obtained in DLT re-drive, as compared to that during initial drive.

The collapse of Space building

On 12 October 2013, the 24-storey high ‘Space’ building collapsed in Medellín, Colombia. The building had a reinforced concrete structure founded on large-diameter piles with enlarged bases. During and after construction the building exhibited structural problems and excessive settlements of some piles. Because of the evidence of structural damage, the building was evacuated on 11 October 2013, 1 day before the collapse. Isolated large-diameter piles excavated in a firm, high-plasticity saprolitic residual clay, supported building columns. Building collapse was triggered by a significant increase of the vertical load transmitted by some columns, which, in turn, is explained by widely different settlements experienced by neighbouring piles and the resulting loading transfer mechanisms. The first part of the paper presents the results of the field exploration and laboratory tests, as well as the structural and architectural layout, including the construction process and other forensic aspects that could influence the collapse of the structure. Afterwards, the joint structure–foundation–soil numerical model developed and its predictions are described. Matching the records of pile settlements, measured during construction and afterwards until building collapse, with model predictions allowed the validation of the model. The causes that triggered the collapse were identified and some other lessons were learned.

Monopile foundation under lateral cyclic action. Numerical modelling

Foundation of an off-shore wind mill is submitted throughout its existence to a very high number of cycles coming from lateral actions such as waves or wind. These actions have a strong aleatory character which makes them very hard to predict, quantify and analyse. Therefore, in current design practice, these actions are being considered as pseudo-static force at their maximum values, with the cyclic phenomenon being neglected. This can lead to an inappropriate design of the foundation, which could have a negative impact on the future structure. This type of structure is generally built on a monopile foundation, a single, large diameter pile, which will be submitted to thousands lateral cycles. The pile diameter plays an important role, influencing the behaviour of the entire structure. Centrifuge experiments on small-scale models are very useful to study such complex problem as piles under lateral cyclic loads. Several researches have been carried out internationally and the results can be used for calibrating numerical models, which is obviously a more accessible method of design, compared to an experimental approach. This has been precisely the starting point of this paper. The purpose of the present paper is to analyse the influence of the pile diameter, by using a FEM a numerical model, previously calibrated based on centrifuge experiments carried out at IFSTTAR Nantes. For the numerical modelling the software CESAR-LCPC 3D has been used. Several pile diameters have been considered, as follows: 0.72 m, 1.08 m, 1.44 m, 1.80 m, 2.16 m and 2.52 m. The results are taking into account the lateral displacement and bending moment of the piles, for static and cyclic loading. The main objective was to determine the stabilisation rate of the most important two design elements (pile head displacement and maximum bending moment) after “n” cycles and to eventually conclude the diameter value beyond which no more influence of cycles is recorded. The numerical model considered 15 cycles and the results have been used extrapolated in order to determine the cycle “n” of stabilisation (for displacement and bending moment).

Analysis of Factors Affecting Bearing Capacity of Large Diameter Single Piles of Offshore Wind Power under Earthquake Loads

The offshore wind turbine single pile foundation structure is simple and easy to install, but in the earthquake environment, large horizontal displacement is easy to occur, which affects the safe operation of offshore wind turbines. For this reason, the bearing characteristics and influencing factors of large-diameter single-pile offshore wind power under earthquake load are analyzed. The Mohr-Coulomb model is used as the model. The ABAQUS is used to construct the large-scale single-pile finite element model of offshore wind power. Loads and analysis of bearing characteristics and influencing factors of large-diameter single-pile offshore wind power under seismic loading. It is found that the increase of pile foundation depth will significantly reduce the horizontal displacement at the top of single pile. After increasing to a certain extent, it has no significant effect on the development of horizontal deformation of large diameter single pile; with the increase of pile diameter and wall thickness, The deformation of large diameter single pile foundation is reduced, but the influence of the pile foundation thickness on the horizontal deformation of the large diame-ter single pile foundation is no longer significant.

THE EXPERIENCE DIFFERENT OF PILING TESTING ON PROBLEMATICAL SOIL GROUND OF ASTANA, KAZAKHSTAN

At the present time, in Astana city is going on works by construction public transport system LRT (Light Railway Transport). LRT is an overhead road with two railway lines. The first stage of construction is including construction of overhead road (bridge) with 22,4 km length and 18 stations. The foundation of bridge is the bored piles with cross-section 1.0HL5 m and length 8-КЗ 5 m. In these conditions, very important to control integrity of concrete body of each bored piles. For checking integrity- applying two methods - Low Strain Method and Cross-Hole Sonic Logging. The aim of this paper is to discuss the advantages and disadvantages of each method using the examples of a real application. The article presents loading tests of large diameter and deep boring piles on the construction site in new capital city of the Republic of Kazakhstan. Finally, some recommendations for testmg methods suitable for problematical ground conditions of Kazakhstan are introduced. Traditionally, pile load tests in Kazakhstan are carried out using static loading test methods. Static pile loading test is the most reliable method to obtain the load-settlement relation of piles. Results of static pile tests using the static compression loading test (by ASTM). static loading test (by GOST) and bi-direction static loading test (by ASTM) methods are presented in this paper. Experienced bored piles with length of 31.5 m. diameter 1000 mm. Hereafter the results of underground testmg by the piles with the methods of vertical static tests of SLT. BDSLT and SCLT are presented, which had been made on Expo 2017 projects, buildings of Pavilion m Astana. Kazakhstan.