scholarly journals Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

2021 ◽  
Author(s):  
Qiang Li ◽  
Kenneth Gavin ◽  
Amin Askarinejad ◽  
Luke J Prendergast
Keyword(s):  
Slenderness Ratio ◽  
Offshore Wind ◽  
Combined Loading ◽  
Initial Stiffness ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Lateral Capacity ◽  
Vertical Loading ◽  
Load Tests ◽  
Observed Behaviour

The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased, and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below ≈ 45% of the pile’s ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour.

Experimental Investigation Into Pile Diameter Effects of Laterally Loaded Mono-Piles

2011 ◽  
Author(s):  
Etienne A. Alderlieste ◽  
Jelke Dijkstra ◽  
A. Frits van Tol
Keyword(s):  
Cyclic Load ◽  
Large Diameter ◽  
Load Control ◽  
Geotechnical Centrifuge ◽  
Lateral Capacity ◽  
Current Test ◽  
Pile Diameter ◽  
Validity Range ◽  
Load Tests ◽  
Laterally Loaded

This paper presents the results of model tests on laterally loaded mono-pile foundations in sand. The tests have been performed in a geotechnical centrifuge. The objective of the research is to quantify large diameter effects of these mono-piles on the lateral capacity and the stiffness response for cyclic lateral loading. These large diameters are out of the validity range of the commonly used design methods. For this reason prototype pile diameters up to 4.4 m with a length over diameter ratio of 5 have been investigated. The results show an increase in pile diameter from Ds = 2.2 m to Dl = 4.4 m leads to a significant increase in static lateral capacity and stiffness from cyclic load tests. All tests have been performed with constant L/D = 5, Id = 60% and a load eccentricity up to e = 4.8 m. However, the current test series needs to be extended to higher initial densities and the load control should be more strictly regulated before a clear diameter dependence, for pile diameters > 2.2 m, is proven.

Physical modelling of the push-over capacity of a jack-up structure on sand in a geotechnical centrifuge

2009 ◽  
Vol 46 (2) ◽  
pp. 190-207 ◽  
Author(s):  
B. Bienen ◽  
M. J. Cassidy ◽  
C. Gaudin
Keyword(s):  
Wind Waves ◽  
Physical Modelling ◽  
Three Dimensions ◽  
Combined Loading ◽  
Silica Sand ◽  
Foundation Soil ◽  
Experimental Development ◽  
Dense Sand ◽  
Geotechnical Centrifuge ◽  
Jack Up

Offshore jack-up drilling rigs are subjected to loading from wind, waves, and current in addition to their self-weight. This applies combined loading in all six degrees-of-freedom in space on the footings. Although the foundation–soil interaction is crucial to the overall response of a jack-up structure, current state-of-the-art models to predict jack-up footing behaviour, developed using data from single footing experiments, have not been validated for such multi-footing systems under general combined loading. This paper introduces the experimental development of a three-legged model jack-up and loading apparatus designed to investigate the rig’s response — in particular the footing load paths — under combined loading in three dimensions. Push-over experiments were performed in a geotechnical beam centrifuge on silica sand. Experimental results of two tests on dense sand are discussed, highlighting differences in response and mode of failure depending on the loading direction of the jack-up. The importance of three-dimensional modelling is also stressed by experimentally demonstrating that the symmetric load case is not necessarily conservative.

Investigating the Response of Offshore Foundations in Soft Clay Soils

2002 ◽  
Author(s):  
B. W. Byrne ◽  
M. J. Cassidy
Keyword(s):  
Soft Clay ◽  
Offshore Wind ◽  
Combined Loading ◽  
Offshore Wind Turbines ◽  
Combined Load ◽  
Vertical Loading ◽  
Load Response ◽  
Drilling Rigs ◽  
Jack Up

A series of tests were conducted in a drum centrifuge with the aim of investigating the performance of typical offshore foundations on soft normally consolidated clay. The foundations consisted of spudcan footings and suction caissons. These types of foundations are being considered for use in various offshore applications including as foundations for mobile drilling rigs (jack-ups) and offshore wind turbines. A special loading device was designed so that combined loading could be applied to the footing. This device could apply the same ratio of horizontal to moment loading as that applied to the foundations of mobile drilling units. The main aim of the investigation was to compare how the performance changes as the foundation is varied. This is important when considering the use of a jack-up rig for a permanent facility, a concept that is increasingly being considered. In such a case there are concerns about the long-term suitability of the spudcan footing, with the amount of sustainable rotational fixity being of particular interest. A total of 64 experiments were carried out investigating areas that include a) comparing the vertical loading response in both compression and tension, b) using a fixed arm to apply predominantly horizontal loading, and c) using a hinged arm to apply a distinct ratio of horizontal to moment loading. Interestingly in the case of the spudcan footing considerable back-flow of the soil was observed during the installation phase. The combined load response of spudcans under these conditions is an area that has not been investigated thoroughly.

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

2018 ◽  
Vol 4 (9) ◽  
pp. 1996 ◽  
Author(s):  
Muqdad Abdallah Kahribt ◽  
Jasim M. Abbas
Keyword(s):  
Lateral Displacement ◽  
Slenderness Ratio ◽  
Offshore Structures ◽  
Lateral Loading ◽  
Loading Conditions ◽  
Lateral Loads ◽  
Dense Sand ◽  
Lateral Response ◽  
Loading System ◽  
Vertical Displacements

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. 

scholarly journals Numerical Study of Laterally Loaded Piles in Soft Clay Overlying Dense Sand

2021 ◽  
Vol 7 (4) ◽  
pp. 730-746
Author(s):  
Amanpreet Kaur ◽  
Harvinder Singh ◽  
J. N. Jha
Keyword(s):  
Layer Thickness ◽  
Soft Clay ◽  
Bending Moment ◽  
Layered Soil ◽  
Clay Layer ◽  
Pile Groups ◽  
Dense Sand ◽  
Lateral Capacity ◽  
Laterally Loaded ◽  
Pile Length

This paper presents the results of three dimensional finite element analysis of laterally loaded pile groups of configuration 1×1, 2×1 and 3×1, embedded in two-layered soil consisting of soft clay at liquid limit overlying dense sand using Plaxis 3D. Effects of variation in pile length (L) and clay layer thickness (h) on lateral capacity and bending moment profile of pile foundations were evaluated by employing different values of pile length to diameter ratio (L/D) and ratio of clay layer thickness to pile length (h/L) in the analysis. Obtained results indicated that the lateral capacity reduces non-linearly with increase in clay layer thickness. Larger decrease was observed in group piles. A non-dimensional parameter Fx ratio was defined to compare lateral capacity in layered soil to that in dense sand, for which a generalized expression was derived in terms of h/L ratio and number of piles in a group. Group effect on lateral resistance and maximum bending moment was observed to become insignificant for clay layer thickness exceeding 40% of pile length. For a fixed value of clay layer thickness, lateral capacity and bending moment in a single pile increased significantly with increase in pile length only up to an optimum embedment depth in sand layer which was found to be equal to three times pile diameter and 0.21 times pile length for pile with L/D 15. Scale effect on lateral capacity has also been studied and discussed. Doi: 10.28991/cej-2021-03091686 Full Text: PDF

Numerical investigation of the monotonic drained lateral behaviour of large diameter rigid piles in medium dense uniform sand

Géotechnique ◽  
2021 ◽  
pp. 1-39
Author(s):  
Huan Wang ◽  
M. Fraser Bransby ◽  
Barry M. Lehane ◽  
Lizhong Wang ◽  
Yi Hong
Keyword(s):  
Numerical Investigation ◽  
Load Transfer ◽  
Large Diameter ◽  
Offshore Wind ◽  
Soil Pressure ◽  
Lateral Capacity ◽  
Pile Diameter ◽  
Centrifuge Tests ◽  
Lateral Response ◽  
Loading Eccentricity

This paper presents a numerical investigation of the monotonic lateral response of large diameter monopiles in drained sand with configurations typical of those employed to support offshore wind turbines. Results from new centrifuge tests using instrumented monopiles in uniform dry sand deposits are first presented and used to illustrate the suitability of an advanced hypoplastic constitutive model to represent the sand in finite element analyses of the experiments. These analyses are then extended to examine the influence of pile diameter and loading eccentricity on the lateral response of rigid monopiles. The results show no dependency of suitably normalized lateral load transfer curves on the pile diameter and loading eccentricity. It is also shown that, in a given uniform sand, the profile with depth of net soil pressure at ultimate lateral capacity is independent of the pile diameter because of the insensitivity of the depth to the rotation centre for a rigid pile. A normalization method is subsequently proposed which unifies the load-deflection responses of different diameter rigid piles at a given load eccentricity.

scholarly journals Evaluation of soil models for improved design of offshore wind turbine foundations in dense sand

Géotechnique ◽  
2020 ◽  
Vol 70 (8) ◽  
pp. 682-699
Author(s):  
Hans Petter Jostad ◽  
Birgitte MISUND Dahl ◽  
Ana Page ◽  
Nallathamby Sivasithamparam ◽  
Hendrik Sturm
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Dense Sand ◽  
Improved Design

Investigating Novel Foundations for Offshore Windpower Generation

2002 ◽  
Author(s):  
B. W. Byrne ◽  
G. T. Houlsby
Keyword(s):  
Wind Turbines ◽  
Oil And Gas ◽  
Wind Farms ◽  
Design Guidelines ◽  
Engineering Problem ◽  
Offshore Wind ◽  
Combined Loading ◽  
Loading Conditions ◽  
Moment Load ◽  
The Uk

In recent years there has been a worldwide increase in the pressure to develop sources of renewable energy. The UK government is committed to ensuring that ten percent of UK energy consumption will be supplied by renewables by the year 2010. Central to this commitment is the need to develop wind farms particularly in the offshore environment. Moving offshore will allow very large wind turbines capable of supplying 2 MW (first generation) to 5 MW (second generation) of power to be installed in large farms consisting of up to fifty or more turbines. In contrast to typical oil and gas structures the foundation may account for up to forty percent of the projected installed cost. The weight of each structure is very low, so the applied vertical load on the foundation will be small compared to the moment load derived from the wind and waves. Further, it will be necessary to have a single design that can be mass-produced over each site rather than have each foundation individually engineered. In combination these points lead to a very interesting engineering problem where the design of the foundation becomes crucial to the economics of the project. One solution is to use conventional piling. However, at some sites it may prove more economical to use shallow foundations, and, in particular suction installed skirted foundations [1]. It will be necessary to develop an adequate design framework for these no vel foundations under the relevant combinations of load so that the optimum structural configuration can be achieved. At Oxford University a program of research on skirted foundations has been underway for the last five years, and much progress has been made on the understanding of this type of foundation under combined loading. This progress has been in both experimental and theoretical areas. This paper explores various structural options that might be used for the wind turbine application. These different options lead to different loading conditions on the foundations. Experiments investigating these different loading conditions are explored. A theoretical approach that describes the experimental results in a way that can be implemented in typical structural analyses programs is outlined. Finally details of a major research program into developing the necessary design guidelines for foundations for offshore wind turbines is described.

Instrumented load tests in mudstone: pile capacity and settlement prediction

2002 ◽  
Vol 39 (6) ◽  
pp. 1254-1272 ◽  
Author(s):  
J R Omer ◽  
R Delpak ◽  
R B Robinson
Keyword(s):  
Load Transfer ◽  
Load Capacity ◽  
Large Diameter ◽  
Soft Rock ◽  
Site Investigation ◽  
Alternative Methods ◽  
Vertical Loading ◽  
South Wales ◽  
Pile Design ◽  
Load Tests

The present work stems from the design of a viaduct in South Wales, U.K., where full-scale pile testing was carried out to assess whether the proposed design methods would meet the required load capacity and settlement criteria for the working piles. Five fully instrumented large diameter bored cast in situ piles, up to 30 m deep, were installed in weathered mudstone and tested under vertical loading. A sixth pile, which had no shaft instrumentation, was formed with a voided toe. In conjunction with vast soil data from 218 site investigation boreholes, the extensive data produced from the load tests were analyzed to quantify the key parameters considered to influence load transfer and settlement behaviour. Each pile was first calibrated using four methods to establish the as-built stiffness, taking into account the nonlinearity of concrete and the effect of partial steel encasement. It is demonstrated that the current national norms for bored pile design in cohesive soil – soft rock are overconservative for South Wales ground conditions. To ameliorate this, alternative methods are proposed, which lead to improved reliability and accuracy in shaft and base capacity assessment. In addition, a numerical model is developed that can be used to predict the complete load-settlement variation up to the ultimate state. The model is sufficiently expounded to allow its immediate application in pile design by geotechnical engineers.Key words: piled foundations, load tests, bearing capacity and settlement, Mercia mudstone.

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