Large-diameter Piles Research Articles

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.

Large-diameter piles in chalk – part 2, design and construction

The design of a 60-storey tall residential tower with a two-level basement in east London has had to take account of two London Underground tunnels which pass beneath the centre of the site, resulting in ‘working’ pile loads of up to 45 MN. The foundation solution comprised a stiff raft with cast in situ bearing piles up to 2·4 m dia. and 61 m long founding in the grade A/B chalk stratum. Some piles, using bentonite support fluid, needed to be constructed within the tunnel exclusion zones, which required a concession from London Underground. This paper presents the Osterberg-cell preliminary pile load test and results, foundation design, working pile construction and limitations on piles constructed in the London Underground exclusion zones. The paper also discusses the control on the bentonite support fluid properties and monitoring of its properties during pile construction.

Large-diameter piles in chalk – part 1, ground investigation

Deep bored piled foundations were planned to support a new 279 m tall tower in east London. The piles were founded in chalk, and therefore detailed stratigraphical logging of the chalk strata was carried out using known marker bands such as flints bands and marl seams. This helped to develop a ground model, including the separation of the various chalk formations into their respective beds. Other investigation methods were employed to assist in developing the chalk stratigraphy, including downhole geophysical techniques, fluid temperature, fluid flow, resistivity, density, caliper and natural gamma. Other downhole tools, such as downhole optical imaging, were also used. Critical to the design of the pile was understanding the behaviour of the bentonite support fluid when used in chalk. Owing to concerns regarding the possible interaction of the bentonite with the chalk, bespoke laboratory tests were carried out on core samples using two commonly used bentonite types. The tests were carried out at two bentonite concentrations with chalk samples from three depths. Control samples were also tested without chalk. This paper presents the detailed investigation of the chalk and its interaction with the bentonite carried out prior to the commencement of the pile design.

Load Transfer Calculation and Analysis of Large-Diameter Bored Piles According to Rules Based on Test Pile Measurement

This study aims to establish an appropriate method to calculate the bearing deformation of large-diameter bored piles in alluvial deposits with soils characterized mainly by medium-dense to dense silt, fine sand, and plastic to hard plastic silty clay in the middle and lower reaches of the Yellow River. According to the field measurement results of 18 large-diameter bored piles in six sites of the third-ring expressway project in Zhengzhou, this study discusses the action laws of pile shaft friction with pile-soil shear displacements and pile tip resistances with pile end displacements. A pile shaft load transfer model and pile tip bearing model are then established for large-diameter bored piles. The calculation parameter values are also given. The feasibility and rationality of the calculation method are verified by an engineering example. According to the engineering example and by changing the parameters of the pile diameter and pile length, the properties of bearing capacities and deformations of the large-diameter bored piles under this site condition are further analyzed. Results show that the inflection point of the pile Q~s curve is obvious for large pile diameters. The pile bearing capacity and deformation property are significantly improved by increasing the pile diameter under a small load. The increase amplitude of the pile bearing capacity and deformation property obviously decreases with the increase in pile length. This result indicates that the improvement of the pile bearing capacity and deformation property by increasing the pile length is not effective. The pile without grouting shows an obvious puncture damage model. Moreover, the settlement of the pile without grouting is small with a large pile diameter or short pile length. The effective length and bearing capacity of a large-diameter bored pile can be greatly increased by pile tip post grouting. The increased value of the pile bearing capacity is high with a large pile diameter and pile length under pile tip post grouting conditions.

Evaluation of p-y Approaches for Large-Diameter Piles in Layered Sand

Evaluation of p-y Approaches for Large-Diameter Piles in Layered Sand

The Loading Test on the Singe Pile with Pile Cap in Transparent Soil Model

Pile-cap-soil interaction is important to understand the load transfer mechanisms of pile foundations. However, studies on pile-cap-soil interactions are quite limited. This article reports a series of small-scale model tests in laboratory that was carried out on the single piles with and without pile caps. Transparent soils made of fused quartz and refractive index–matching fluids are employed to represent natural angular sand. Pile cap effects, diameter effects, and pile length effects are investigated. Elastic load limits are found to increase linearly with pile cap area, pile length, and pile diameter for the tested pile models. Soil deformation around the pile head is greatly influenced by the pile cap size, pile diameter, and pile length. Soil deformation at the pile head can be described by Terzaghi’s bearing capacity failure theory. The soil particles below the pile cap next to the pile body move downward, which might reduce the shaft friction or induce the negative shaft friction. All the loading tests show that the pile cap can increase the pile’s bearing capacity. For small-diameter model piles, soil deformation is centered below the pile base, no sliding surfaces are formed at the pile base when settlement S = 4 mm. For large-diameter piles, it is possible that a bearing capacity failure forms two sliding surfaces on the left and right of the pile base. This study indicates that the appropriate usage of the bearing resistance of soils below the pile cap can increase the bearing capacity of pile foundations. This study reveals the soil deformation below the pile cap, which benefits the utilization of the bearing resistance of pile caps. The soil deformation zone at the pile head and around the pile base is also investigated.

A non-collocated method to quantify plastic deformation caused by impact pile driving

The use of bolted connections between the tower and a support structure of an offshore wind turbine has created the need for a method to detect whether a monopile foundation plastically deforms during the installation procedure. Small permanent deformations are undesirable, not only because they can accelerate fatigue of the structure; but also because they can lead to misalignment between the tower and the foundation. Since direct measurements at the pile head are difficult to perform, a method based on non-collocated strain measurements is highly desirable. This paper proposes such a method. First, a physically non-linear one-dimensional model is proposed, which accounts for wave dispersion, effects that are relevant for large-diameter piles currently used by the industry. The proposed model, combined with an energy balance principle, gives an upper bound for the amount of plastic deformation caused by an impact load based on simple strain measurements. This is verified by a lab-scale experiment with a uni-axial stress state. Second, measurement data collected during pile driving of a large-diameter pile show that the proposed one-dimensional model, while able to predict the peak stresses, fails to accurately predict the full time history of the measured stress state. In contrast, an advanced model based on shell membrane theory is able to do that, showing that a bi-axial stress state is needed for these type of structures. This requires an extension of the theory for plasticity quantification presented in this paper.

Review Study on the Status of Bearing Characteristics of Large Diameter Pile Foundation

With the rapid development on the construction of the highways, high-speed railway, large bridges and other large-scale projects, large diameter piles have been widely used in various projects. Based on collecting and sorting the related research literature on the load-bearing characteristics of large diameter pile foundations at home and abroad, the present situation and problems of research on the bearing capacity of large diameter pile foundation are analysed from the theoretical analysis, experiment and numerical simulation, etc. in this paper. Through the study, it was found that there is some difference on the deformation characteristics, mechanical characteristics and law of pile soil interaction between large diameter pile foundation and small-medium diameter pile. At present, the bearing characteristics of large diameter pile theory study still lag behind the engineering application. In particular, the bearing characteristics of contact surface of large diameter pile foundation and the mechanical properties under dynamic loading should be further studied, which will provide certain support for the design and optimization of large diameter pile foundation.

Evaluation of FHWA Pile Design Method against the FHWA Deep Foundation Load Test Database Version 2.0

The efficacy of the FHWA pile design method was explored using data made possible by the 2017 release of FHWA Deep Foundation Load Test Database (DFLTD) v.2. Information contained within DFLTD v.2 was leveraged to evaluate the most common pile design methods against failure loads obtained via in situ static load testing procedures. In the process, the authors developed a custom relational database and software to batch process the available information. The scope was limited to impact-driven, un-tapered, steel and concrete piles, loaded in compression, using a static load test. DFLTD v.2 contains 3,116 unique-combination project/exploration/foundation/test cases of which 213 contained sufficient data to permit batch processing of the results to compute the axial load capacity and interpret the static failure load, according to the study scope. Scatter between measured (interpreted) and predicted capacities is significant; the computed capacity was off by a factor of 2 in many tests. The range in calculated to measured capacities ( Qc/Qm) was from 0.12 to 8.88, and the mean Qc/Qm was 1.48. Preliminary evaluation suggests that the method performs better in clay than in sand, and overpredicts the capacities of long and larger diameter piles. The authors trust that this study will permit engineers and state agencies to better understand the efficacy of the most commonly employed design methods, resulting in a more resilient infrastructure.

Dynamic response of a large-diameter pile with variable section in layered saturated soil considering construction disturbance effect

ABSTRACTAn analytical solution is developed in this paper to investigate the vertical time-harmonic response of a large-diameter variable-section pile, and it considers the radial inhomogeneity of the surrounding soil caused by construction disturbance. First, the saturated soil surrounding the pile is described by Biot’s poroelastic theory and a series of infinitesimally thin independent layers along the shaft of the pile, and the pile is represented by a variable-section Rayleigh–Love rod. Then, the dynamic equilibrium equations of the soil and pile are solved to obtain an analytical solution for the impedance function at the pile top using the complex stiffness transfer method and impedance function transfer method. Finally, the proposed solution is compared with previous solutions to verify its reliability, and a parameter study is conducted to provide insights into the sensitivity of the vertical dynamic impedance of the pile and velocity response in low-strain integrity testing on defective piles.

A new measurement approach for deflection monitoring of large-scale bored piles using distributed fiber sensing technology

A novel distributed fiber optic strain sensing technology, named Brillouin optical time-domain analysis (BOTDA), has been used to study the performance of large-diameter bored piles subjected to a slope excavation in Hong Kong. A new installation method for the distributed fiber optic sensors (FOS) in the bored piles was proposed in this study. Distributed strains along the instrumented bored piles were obtained by BOTDA sensors during multi-stage excavations. Details of sensor design, field installations, sensor protections, and data analysis are presented in this paper. Axial and bending strains along the instrumented pile were obtained by two sets of BOTDA sensors installed on diametrical opposite sides along the pile. The calculation method for deriving the lateral deflections from distributed strains is described. Thus, the calculated lateral deflections from BOTDA sensors were compared with the traditional inclinometers which were installed at the center of the same instrumented bored pile. Measurements obtained from the BOTDA sensors were found to be in good agreement with the inclinometer data. The maximum lateral wall deflection over the excavation depth was between 0.05% and 0.1%. The lessons learned from this field implementation are discussed and suggestions provided for further similar applications. Field application in this study reveals that the BOTDA measurement has great potential to be used for performance monitoring of large diameter piles.

Applicability of Timoshenko, Euler–Bernoulli and rigid beam theories in analysis of laterally loaded monopiles and piles

In various analytical, semi-analytical and numerical studies on laterally loaded piles, the pile is conventionally modelled as an Euler–Bernoulli beam. Modelling large-diameter monopiles and piles using the Euler–Bernoulli beam theory may not be appropriate, because the Euler–Bernoulli beam theory is strictly valid for long, slender piles and does not account for shear deformations, which may have a significant effect on the lateral pile response of large-diameter piles. In order to investigate the effect of shear deformation in the modelling of monopiles and piles, a framework for static analysis of laterally loaded piles is developed, in which the monopile/pile is modelled using the Timoshenko beam theory and the soil as an elastic continuum. A rational soil displacement field is assumed and the differential equations of pile and soil displacements are obtained using calculus of variations. Solutions are obtained analytically and numerically following an iterative scheme. The analysis framework also incorporates the Euler–Bernoulli and rigid beam theories as progressive simplifications of the Timoshenko beam theory. Pile responses obtained using the three beam theories are compared with three-dimensional finite-element analysis to establish the relative accuracies of each beam theory in predicting lateral pile response. Systematic parametric studies are performed to establish which beam theory is most appropriate to model laterally loaded monopiles and piles, particularly the large-diameter piles, and to find out the range of applicability of the different beam theories in predicting lateral pile response. The Timoshenko beam theory can be used for all cases of laterally loaded piles to produce the most accurate results, particularly for piles with hollow cross-sections. The Euler–Bernoulli beam theory produces accurate results for most piles with solid cross-sections. The rigid beam theory can be used for a quick initial estimate of pile head displacement, particularly for piles with high values of relative pile–soil stiffness ratio.

Experimental and Numerical Research of Stress-Strain State of Homogeneous Soil Massif at Interaction with Single Barrette

Deep foundations are used for the design of high-rise buildings due to a large pressure transfer on the soil base. The foundations of buildings sometimes use barrettes which are able to perceive significant vertical and horizontal loads due to improved lateral surface. Barrettes have increased load bearing capacity as compared with large diameter piles. In modern practice the interaction between barrettes and soil is investigated by analytical and numerical methods and has no sufficient experimental confirmation. The review of experimental methods for the research of the intense stress-strain state of the uniform soil massif at interaction with elements of a deep foundation is provided in this article. Experimental research are planned with the use of laboratory stand for the purpose of qualitative data obtaining on the interaction barrettes with an assessment of a settlement model adequacy and also at the research of the intense stress-strain state by numerical methods.

Design and fatigue analysis of monopile foundations to support the DTU 10 MW offshore wind turbine

This study aims to investigate the challenges and feasibility of extending monopile technology for larger wind turbines and deeper water.Preliminary monopile designs to support the DTU 10 MW reference wind turbine were established for water depths 20 m, 30 m, 40 m and 50 m. To properly account for the pile-soil interaction and the rigid pile behavior of large-diameter piles, lateral soil stiffness was derived using the finite element software Plaxis 3D.To verify the preliminary design, FLS analyses were done using the SIMO-RIFLEX computational tool. As the water depth increases, the contribution of hydrodynamic loads to fatigue damage is found to be larger. A method for predicting total fatigue damage using fewer representative sea states was introduced: a fatigue Damage Parameter (FDP) was established to correlate fatigue damage to environmental condition by means of thrust, significant wave height (Hs) and wave peak period (Tp), and to select representative conditions. Using at least 30% of the total number of conditions resulted in at least 90% accuracy in damage prediction.

Dynamic behavior of large-diameter piles with considering liquefaction under clay layer

Marine structures are mostly constructed on deep foundations, namely large-diameter piles. Such support structures are driven into deposits of saturated granular soil, which is vulnerable to liquefaction under loadings of dynamic nature, e.g., earthquakes. Although numerous studies have been accomplished to obtain a comprehensive understanding of their performance during liquefaction, a conclusive study has not been presented for the specific case of large-diameter piles under a clay layer. This issue has great importance in case of offshore wind turbines, since they are very sensitive to dynamic loadings. In this study, a 3D FEM model was constructed by OpenSeesPL to explore soil and pile responses throughout liquefaction. To capture the precise behavior, a constitutive law based on a multi-surface plasticity was utilized for soil. The described model used in this study is capable of accurate prediction of sand behavior in undrained conditions. Different scenarios were tested: variations in pile dimensions, loading frequency and influence of clay layer. Sensitivity analyses show that loading frequency, presence of clay layer and pile diameter could significantly affect behavior of large-diameter piles in saturated soil conditions.

Field tests of large-diameter rock-socketed bored piles based on the self-balanced method and their resulting load bearing characteristics

Owing to the capacity limitations of reaction systems for field loading tests, it is very difficult to carry out ultimate load tests on large-diameter rock-socketed bored piles in mountainous areas. Therefore, the self-balanced loading test method was used in this study to determine the load capacity of large-diameter rock-socketed bored piles. Distributed optical fibre test technology was used to explore the mechanical behaviour of the piles, and steel strain gauges and sliding micrometres were used for comparison. The test results indicate that the self-balanced loading test method can effectively circumvent the limitations of reaction systems in traditional loading tests. The axial force distribution in the pile shaft along the length of the pile was found to exhibit a non-linear distribution with increasing depth that transmitted higher loads deeper and deeper along the piles as the applied loads were increased. Finally, pile shaft resistance was found to develop prior to pile tip resistance, with the shaft load share ratio decreasing as the tip load share increases with the increase in load. Furthermore, the reliability of distributed optical fibre technology for determining the load bearing characteristics of large-diameter rock-socketed bored piles in complex geological conditions is confirmed.

Deformation mechanisms for offshore monopile foundations accounting for cyclic mobility effects

There has been a huge surge in the construction of marine facilities (e.g., wind turbines) in Europe, despite the many unknowns regarding their long-term performance. This paper presents a new framework for design strategy based on performance measures for cyclic horizontally loaded monopile foundations located in saturated and dry dense sand, by considering pile deformations and pore pressure accumulation effects. A three-dimensional finite element model was developed to investigate the behavior of large-diameter piles. The model accounts for nonlinear dynamic interactions in offshore platforms under harsh combined moment and horizontal environmental loads, with emphasis on the cyclic mobility of the surrounding cohesionless subsoil and associated shear.The maximum moment applied in the cyclic analyses is varied from 18% to 47% of the ultimate resistance. The considered data reflect behavior at the expected load amplitudes and cycle numbers during the service life of operation.For low numbers of load cycles (<1000 cycles), there were no differences between the power law and logarithmic approaches in terms of describing the accumulated deformations; however, for high numbers of cycles (<10,000 cycles), the logarithmic law was less suited to describe the accumulation response. Magnitude of cyclic loads was found to cause a linear increase in the accumulated rotation. The results from short-term and long-term dynamic response of monopiles indicate that few load cycles with higher load levels are the main concerns in accumulation of pile rotation rather than thousands of load cycles with low amplitudes.