Bearing Capacity Of Bucket Foundation Research Articles

The influence of the soil plug on the bearing capacity of bucket foundations in clay

ABSTRACT The soil plug is a common problem in the installation of bucket foundations for offshore wind turbines (OWTs), but there is little research about the influence of the soil plug on the bearing performance of bucket foundations. In this paper, the range of soil plug height is firstly determined according to the recordings of engineering cases and geotechnical tests in the published literature. Then the finite element models of bucket foundations with different soil plugs are established to investigate the influence of the soil plug on uniaxial and combined bearing capacities under different soil properties and embedment ratios. Based on the numerical results, a bearing capacity calculation method of bucket foundations considering the effect of soil plug is proposed. The proposed equivalent method can be used to evaluate the influence of the soil plug on the bearing capacities of bucket foundations.

Numerical analysis of lateral – Moment capacity of bucket foundations for offshore wind turbine in sand

This paper reports the lateral – moment bearing capacity of bucket foundations under lateral loading in sand. The Modified Mohr-Coulomb (MMC) model is adopted to capture the hardening – softening behaviour in medium dense and dense sands within a finite element (FE) modelling framework. The FE model performance is assessed against available field test data as well as analytical solutions showing a relatively good agreement. A series of parametric study is conducted to investigate the effects of bucket aspect ratio, bucket diameter, load eccentricity, vertical load and relative density of sand on the lateral - moment bearing capacity of the bucket. Comparisons are drawn between the conventional Mohr-Coulomb (MC) model and the stress dependent MMC model highlighting the role of sand dilatancy in mobilising the lateral moment capacity. Based on the FE results, a simple stepwise calculation framework is proposed for two scenarios: (i) to predict the lateral - moment bearing capacity of the bucket if the bucket dimensions are known, and (ii) to design the bucket dimensions for a known required bucket capacity.

Combined bearing capacity of bucket foundations in soft-over-stiff clay

In this study, a series of three-dimensional small-strain analyses are carried out to explore the combined capacity of bucket foundations in soft-over-stiff clay under general loading. It aims to provide a supplement to existing design codes. Numerical models are generated and validated with existing data in open literature, where good agreements are obtained. The effects of the layered deposit are explored, including the thickness of the upper soft clay, the length of skirt, the magnitude of the vertical load, and soil properties. Due to the presence of soft clay, the uniaxial bearing capacities reduce significantly, reaching as low as 25% reduction compared to the caisson in uniform stiff clay. In the V-H, V-M and V-H-M spaces, the failure envelopes are normalized in unique shapes according to the geometry of the bucket. Based on the numerical results, an empirical design procedure is proposed to evaluate the failure envelopes of bucket foundations subjected to complex loading conditions in soft-over-stiff clay.

Bearing capacity of bucket foundations in silt-over-clay soil condition under combined V-H-M loading

The bearing capacity of bucket foundations subjected to combined vertical-horizontal-moment loadings (V-H-M) is an important issue for its design and application. This paper investigates the response of bucket foundations under V-H-M loadings in silt-over-clay using small strain finite element method. Model validation is carried out by comparing with previously testing data with good agreement obtained. Then parametric study is conducted to study the effect of embedded ratio, soil property and top layer thickness. It is found that the soil failure mechanism and corresponding bearing capacity of bucket foundations in silt-over-clay are significantly different to that in clay only condition. Approximating expressions are proposed to describe the unique trends of the normalized failure envelopes for bucket foundations in silt-over-clay soil deposits. The findings of this study could help to guide design application of bucket foundations.

Research on the Law of Bearing Capacity of the Bucket Foundation for Offshore Wind Turbines in Clay Soil

Xing, Z.; Fu, P., and Huang., L., 2020. Research on the law of bearing capacity of the bucket foundation for offshore wind turbines in clay soil. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 43–48. Coconut Creek (Florida), ISSN 0749-0208.The bucket foundation can be used as the foundation of high-rise buildings. An in-depth understanding of the bearing capacity of the foundations is critical to ensure reliable design and safe operation of foundation. Based on the load characteristics of high-rise buildings and the parameters of soil, the authors explore the law of the bearing capacity of bucket foundations in clay soil and summarize the impacts of the ultimate horizontal load and the ultimate bending moment load on the failure of the bucket foundation. The research found that the failure mode of bucket foundations in clay soil was mainly caused by rotation, the optimal height-diameter ratio of the bucket foundation was about 0.57, and the envelope curve of horizontal load-bending moment failure was roughly an ellipse.

Effect of honeycomb bulkheads on uniaxial undrained bearing capacities of wide-shallow bucket foundation

In order to study the effect of honeycomb bulkheads on uniaxial undrained bearing capacities of wide-shallow bucket foundation, the finite element models of bucket foundations with and without bulkheads on soft ground were established respectively. A large number of 3D finite element analyses have been performed to obtain uniaxial bearing capacities of the two foundations with different embedment ratios and soil shear strength heterogeneity by using displacement control method. The results show that, for homogenous clay, all the vertical, horizontal and moment bearing capacities of the wide-shallow bucket foundation are not affected by the honeycomb bulkheads. For non-homogenous clay, the moment bearing capacity of the wide-shallow bucket foundation is obviously affected by the honeycomb bulkheads, while the effect for improving the vertical and horizontal bearing capacity of the bucket foundation can be neglected. For the convenience of designers reference, simplified calculation equations for undrained bearing capacities are fitted according to the finite element results.

An investigation into the lateral loading response of shallow bucket foundations for offshore wind turbines through centrifuge modeling in sand

A shallow suction bucket is a new foundation type for offshore wind turbines. Due to its large size and bulky shape, the bucket and the soil within the bucket do not necessarily deform as a whole. Moreover, limited research has been conducted on the hydrodynamic wave influence on the shallow bucket bearing response. These factors pose great challenges to the shallow bucket foundation design. This paper presents a set of centrifuge tests of a shallow bucket model subjected to monotonic and dynamic lateral loads to study the lateral bearing response of shallow bucket foundations in the field under combined loads induced by wind, waves, etc. In addition to the routine measurements (e.g., load-displacement), the soil pressures on the bucket and the distribution and evolution of the excess pore pressures in the surrounding soils are also obtained. The deformation pattern of the bucket (e.g., rotation center) is revealed through displacement measurements. Finally, the proposed easy-to-use analytical equations using the limit equilibrium to assess the bearing capacity of bucket foundations, taking into account the influence of the soil strength degradation caused by hydrodynamic wave loadings, are found to yield good results upon comparison with the centrifuge data, providing useful guidelines for the design of shallow bucket foundations.

Effect of embedment on the vertical capacity of bucket foundation in loose saturated sand: Physical modeling

ABSTRACTBucket foundations have been widely used for a variety of offshore applications. The effects of skirt length on ultimate bearing capacity of bucket foundation have been studied and reported in published scientific papers. However, few studies have addressed the behavior of bucket foundations in loose saturated sand. In this paper, a series of experimental investigations were performed to determine the bearing capacity of bucket foundation under uniaxial loading. The experiments were conducted on small-scale foundations under vertical loading in loose saturated sand. It was found that increasing the skirt length would enhance the bearing capacity of bucket foundation. As reflected in the present study, bearing strength might be enhanced more than 5 times in loose saturated sand in comparison to surface footing with equivalent diameter. Based on the experimental investigation, a depth factor was proposed to approximate bearing capacity of bucket foundations in terms of those for surface footing and embedment ratio. Moreover, the corresponding settlement of foundation at the failure load was found to increase with skirt length.

Experimental and numerical studies on lateral bearing capacity of bucket foundation in saturated sand

The lateral bearing capacity of bucket foundation was studied by tests and FEM. The characteristics of bearing capacity under horizontal loading were obtained experimentally. In this paper the results of the numerical and tests study on the bearing capacity and failure mode of bucket foundations that support wind turbine structures in homogeneous medium sand were presented, considering the frictional contact behavior of interface between skirt and subsoil. The height to diameter ratios (L/D) were taken from 0.3 to 1.0. The results of test and FEM showed that the rotation is the main failure mode of bucket foundation, and the center of rotation changes with the height to diameter ratios. The inclination angle for the ultimate lateral bearing capacity of the wide-shallow bucket foundation is about 3.0°, which is different from small diameter foundations, such as suction anchors and piles. The comparison of results from FEM, tests and simplified calculation method proves the accuracy of the research results.

Vertical bearing capacity of bucket foundation in sand overlying clay

We perform a suite of axisymmetric finite element analyses to study the load transfer mechanism and predict the vertical bearing capacity of bucket foundations in sand overlying clay profiles. We use elasto-plastic soil models following Mohr-Coulomb and Tresca failure criteria for sands and clays, respectively. A non-associated flow rule is used with the Mohr-Coulomb model to realistically simulate the dilatant behavior of sands. A broad range of strength parameters for both sands and clays are used. The aspect ratio and bucket tip-to-clay depth (d) are also varied. The traces of plastic shear strain increments are monitored to observe how the vertical load is transmitted to underlying sand and clay layers, and to study the associated failure surface. The shape of the failure surface is shown to be not unique and display complex pattern conditional on strength parameters, aspect ratio, and d. We present a suite of equations to predict the vertical base capacity. The proposed set of equations provide enhanced estimate of the base capacity compared with theoretical models. We also calculate the shaft resistance of the bucket foundations on multi-layered profiles. The shaft resistance can reliably estimated from an empirical equation developed for bucket foundations in uniform sand.

유한요소해석을 통한 다층지반에서의 버킷기초 수직지지력 산정

유한요소해석을 통한 다층지반에서의 버킷기초 수직지지력 산정

Vertical bearing capacity of bucket foundations in sand

Bucket foundations are widely used to support offshore structures. The vertical capacity of bucket foundations in clays has been extensively studied. However, the unique load transfer characteristics of bucket foundations in sands are not well documented. We perform a series of two-dimensional axisymmetric finite element analyses using the Mohr-Coulomb model following a non-associated flow rule. Because the depth-to-diameter ratio of a bucket foundation is much lower compared with that of a pile, a higher level of arching is shown to occur in the soil. A pronounced increase in the horizontal stress and a corresponding increase in the shaft resistance (Qs) are observed. The arching also causes the failure surface to widen due to additional vertical stress imposed on the soil. Based on numerical results, predictive equations for Qs and a combined shape and depth factor for the base capacity (Qb) are proposed for bucket foundations in sands that follow a non-associated flow rule.

사질토 지반에 설치된 버킷기초 및 얕은기초의 수직지지력 산정

The vertical bearing capacity of a bucket foundation installed in sand can be calculated as sum of the skin friction and end bearing capacity. However, the current design equations are not considering the non-associated flow characteristics of sand and the reduction in the skin friction and increase in the end bearing capacity when the vertical load is applied. In this study, we perform two-dimensional axisymmetric finite element analyses following non-associated flow rule and calculate the vertical bearing capacity of circular bucket foundation of various sizes installed in sand of different friction angles. After calculating the skin friction and end bearing force at the ultimate state, design equations are derived for each. The skin friction of bucket foundation is shown significantly small compared to the end bearing capacity. Considering the difference with the available design equation for piles, it is recommended that the equation for piles is used for the bucket foundation. A new shape-depth factor (s q ?d q ) for bucket foundation is recommended which also accounts for the increment of the end bearing capacity due to skin friction. Additionally, the shape and depth factor of embedded foundation proposed from the associated flow rule can overestimate the bearing capacity in sand, so it is more adequate to use the shape-depth factor proposed in this study.

Negative pressure consolidation of silt inside bucket foundation

A series of model experiments of bucket foundations concerning suction installation and negative pressure consolidation in saturated silt were carried out in a cube steel bin at Tianjin University. The experimental results show that the silt inside the bucket has been strengthened by negative pressure, and the strengthening effect decreases with the increase of the distance from the bucket. A three-dimensional numerical model of the experiments was built by means of finite element software ABAQUS with fluid-solid coupling method. The results show that the bearing capacity of the silt inside the bucket foundation increases significantly at the former stage of negative pressure consolidation, while the increasing trend slows down over time. The rotation centers of the bucket foundation and the inner soil region tend to be closer to each other based on the consolidation. The bearing capacity of the bucket foundation is improved effectively with the increase of soil strength. The effects of negative pressure consolidation on the bearing capacity of bucket foundation were also illustrated by an actual offshore wind power project case.

Study on Bearing Capacity of Bucket Foundation Subjected to Horizontal Loading

Wu, K. and Fan, Q., 2015. Study on bearing capacity of bucket foundation subjected to horizontal loading.The bucket foundation is one parts of offshore platform and is wearing the wave or wind loading which causes the bucket foundation instability to offshore platform falling. So, the numerical simulation, limit analysis and model test are investigated and compared in order to reveal the bearing capacity of bucket foundation under horizontal loading. Based on the three analysis methods compared, it can be observed that: (1) the results of the three methods are in good agreement. (2) The bucket foundation subjected to horizontal loading is rotation and the center of rotation is located in the two-thirds of embedded depth. Under horizontal load, the coherent spoon plastic zone is formed in the bottom of bucket foundation. And, the wedge plastic zone is formed on both sides of the bucket foundation. While, in the same direction with horizontal load of the barrel side is passive area and larger earth pressure is being because of barreling into foundation soil. On the other side of the foundation is active area, which the foundation is separation with soil.

Numerical Studies on the Working Mechanism and Bearing Capacity of Bucket Foundations for Offshore Wind Turbines

Sun, L.; Huo, Z., and Yan, S., 2015. Design of hydraulic telescopic grouted clamp device and analysis of its closing collision.Bucket foundations represent a new type of foundation for offshore wind turbines. They are large cylindrical structures that open at the base and close at the top. Compared with traditional offshore pile foundations, bucket foundations exhibit the advantages of shorter installation periods, lower material costs, and more rational bearing patterns. The complex interaction between a bucket foundation and soil defines the loading mechanism of this foundation type, and its failure mode has yet to be clearly defined. A simplified limit equilibrium method or other oil-platform design codes (e.g., API) is typically adopted to design bucket foundations. However, the simplified limit equilibrium method does not reflect the working characteristics of the soil in the foundation, thus resulting in a relatively considerable deviation. A numerical analysis is performed to simulate the working mechanism and evaluate the bearing capacity behavior of bucket foundations. Calculation results show that the bearing characteristics of bucket foundations are different from those of the simplified limit equilibrium method, and that failure occurs and develops in the soil within the bucket wall. This difference causes the simplified limit equilibrium method to overestimate the bearing capacity of bucket foundations.

Three-Dimensional Finite Element Analysis on the Bearing Capacity of Bucket Foundation with Different Ratios of Diameter to Height

The ABAQUS software is used for simulating the vertical bearing capacity of bucket foundation of different ratios of diameter to height and the analysis for the stress and displacement distribution and load-displacement curve. When the bucket foundation is under pressure, the vertical stress of the soil distribution changes from the bottom to the top, and then spreads to most part of the soil in the bucket foundation. The vertical displacement of the soil develops from the top of foundation and spreads inside, then expands to the outside range, the maximum displacement occurs both at the bottom and inside. According to the analysis of the ultimate bearing capacity of the bucket foundation, it could be found that when the height of the bucket foundation remains unchanged, the ultimate bearing capacity increases with the increasing ratio of diameter to height. If the ratio of diameter to height is less than 1.2, the ultimate strength increases significantly. If the ratio of diameter to height is greater than 1.2, the increasing speed of the ultimate bearing capacity changes slowly. When the diameter of the bucket foundation is constant, the ultimate bearing capacity decreases as the ratio of diameter to height gradually increases, and it decreases at a homogeneous speed. So the ratio of diameter to height 1.2 can be used as the optimum point of the ratio of diameter to height of the bucket foundation.

Study on Deformation Behavior of Bucket Foundation with Marine Soft Soil Materials under Horizontal Loading

The 21st century is the new era which mankind develop and utilize the ocean，In order to exploit and utilize of marine resources，the bucket foundation is emerged under this condition. In the process, a lot of marine soft soil materials is inevitably encountered with in engineering practice. Traditionally, the bucket foundation is only a upside-down bucket and no compartment is set inside. Using the finite element method, this paper makes a systematical expatiation on the research on the horizontal bearing capacity of bucket foundation with marine soft soil materials under cyclic loading conditions.