Capacity Of Suction Caissons Research Articles

On the uncertainty analysis of uplift capacity of suction caissons in clay based on the fuzzy sets theory

Uncertainties in the input parameters of predictive models for uplift capacity of suction caisson lead to uncertain performance. To account for the influence of such uncertainties on the suction caisson stability, a fuzzy model is employed. The input uncertainties are introduced to the predictive formulas by triangular membership functions. To obtain the extreme values of the uplift capacity, optimization problems with many objectives are solved by the coupling of genetic algorithm (GA) with the uplift capacity estimation models. The relationships derived by different methods for the prediction of the uplift capacity, are analyzed by the fuzzy approach using a compiled database. Through the membership functions of several statistical measures, it is inferred that small input uncertainties can significantly affect the responses. Also, the recently proposed “M5-GP” - based prediction models are found to be vulnerable to input uncertainties, hence, a new revision called “Improved M5GP” model is developed. Finally, it is shown that the presented model is the best among various models regarding the reliability as well as the accuracy.

Determination of Uplift Capacity of Suction Caisson Using Gaussian Process Regression, Minimax Probability Machine Regression and Extreme Learning Machine

This article employs Gaussian process regression (GPR), minimax probability machine regression (MPMR) and extreme learning machine (ELM) for prediction of uplift capacity (–) of suction caisson. This study uses GPR, MPMR and ELM as regression techniques. L/d (L is the embedded length of the caisson and d is the diameter of caisson), undrained shear strength of soil at the depth of the caisson tip (Su), D/L (D is the depth of the load application point from the soil surface), inclined angle (θ) and load rate parameter (Tk) have been adopted as inputs of GPR, MPMR and ELM models. The output of GPR, MPMR and ELM is P. The results of GPR, MPMR and ELM have been compared with the artificial neural network (ANN) model. The developed models have also been used to determine the effect of each input on P. This study shows that the developed GPR, MPMR and ELM are robust models for prediction of P of suction caisson.

New design equation for undrained pullout capacity of suction caissons considering combined effects of caisson aspect ratio, adhesion factor at interface, and linearly increasing strength

Undrained pullout capacity of suction caisson in clays with homogeneous and linearly increasing strengths with depth was investigated by two-dimensional axisymmetric finite element analysis. Effects of the caisson aspect ratios, the complete range of adhesion factors at soil-caisson interface, and the full range of dimensionless strength gradients on the dimensionless pullout factor of suction caissons were comprehensively examined. Based on a nonlinear regression to the derived finite element solutions, a new design equation of the undrained pullout capacity of suction caissons was proposed, considering the practical ranges of caisson aspect ratios, the complete range of adhesion factors at soil-caisson interface, and a general profile of both homogeneous and linearly increasing strengths with depth. The proposed equation was validated through a comparison of existing solutions and published experimental data.

Investigation of scour effects on lateral behaviors of suction caisson

ABSTRACTThe use of suction caissons can reduce the development costs of offshore wind energy and has broad application prospects. However scour around marine foundations is inevitable, it gravely affects the stability of marine engineering. Therefore, there is an urgent need to study the weakening effects of scour on suction caisson. In this study, the variation trends of remaining soil parameters (the effective unit weight and the peak effective friction angle) after scour are examined with consideration of the dilatancy and stress history of sandy silt. It is found that the parameters of shallow soil change considerably after scour, and the larger the scour depth, the greater is the change in the parameters. However, the deep soil is less affected. On the basis of these findings, scour effects on the ultimate moment capacity of suction caisson are studied. The ultimate moment capacity is found to greatly reduce under scour, and its calculated value is larger than the actual value when the effects of dilatancy and stress history are ignored. To simplify calculation, it is feasible to replace the ultimate moment capacity when both dilatancy and stress history are considered with that when only dilatancy is considered.

Assessment of cyclic response to suction caisson in clay using a three-dimensional displacement approach

ABSTRACTAn investigation was made to present analytical solutions of cyclic response to suction caisson subjected to inclined cyclic loadings in clay using a three-dimensional displacement approach. A model representing the relationship between vertical load and vertical displacement and that between lateral load and lateral displacement along the skirt of suction caisson subjected to cyclic loadings is proposed for overconsolidated clay. For the effect of vertical load on cyclic load capacity of suction caisson, using the Mindlin solution in the case of a vertical point load, the vertical stress of soil under the base of suction caisson is presented. For the stress state of soil beneath the base of suction caisson subjected to cyclic loading, the Mohr–Coulomb failure line and critical state line are presented and the relationship between total stress, effective mean principal stress, stress difference, and pore-pressure is elucidated. The comparison of results predicted by the present method for a suction caisson subjected to cyclic loadings in clay has shown good agreement with those obtained from field tests. Cyclic behavior of clay up to failure is made clear from the relationship between cyclic tensile load, vertical and lateral displacements, and rotation and that between depth, vertical, and lateral pressures.

Estimating uplift capacity of suction caissons in soft clay: A hybrid computational approach based on model tree and GP

Stability of suction caissons used as foundations or anchors of offshore structures is a critical challenge in marine structures engineering. To this end, many studies have been conducted including those concentrate on implementing computational intelligence methods to model the response of suction caissons under loading. In this regard, this paper aims at formulating uplift capacity of suction caissons using a hybrid artificial intelligence computational tool based on model tree (M5) and genetic programming (GP), called M5-GP. The formulae are developed in terms of several governing parameters using a reliable experimental database from the literature. The results show that the M5-GP based relationships are able to predict the uplift capacity of suction caissons precisely. Furthermore, to consider the safety in the design process, probabilistic equations are also given for various risk levels. The new formulas compare favorably with the existing relationships in the literature regarding prediction performance. In addition, the simplified formulation is compact, easy to use and physically sound. Therefore, it is especially appropriate to be used in design practice.

PREDICTION OF UPLIFT CAPACITY OF SUCTION CAISSON IN CLAY USING FUNCTIONAL NETWORK AND MULTIVARIATE ADAPTIVE REGRESSION SPLINE

Suction caissons are extensively used as anchors for offshore foundation structures. The uplift capacity of suction caisson is an important factor from effective design point of view. In this paper, two recently developed AI techniques, functional network (FN) and multivariate adaptive regression spline (MARS), have been used to predict the uplift capacity of suction caisson in clay. The performances of the developed models are compared with other AI techniques; artificial neural network, support vector machine, relevance vector machine, genetic programming, extreme learning machine and group method of data handling with harmony search (GMDH-HS). The model inputs include the aspect ratio of the caisson, undrained shear strength of soil at the depth of the caisson tip, relative depth of the lug at which the caisson force is applied, load inclination angle and load rate parameter. Comparative analyses are made with the results of the above AI techniques, using different statistical performances criteria; correlation coefficient (R), root mean square error, Nash-Sutcliffe coefficient of efficiency, log-normal distribution of ratio of predicted to observed load capacity, with a ranking system to find out the best predictive model. The FN and MARS models are found to be comparably efficient and they outperform other AI techniques.

Investigation of the load-bearing capacity of suction caissons used for offshore wind turbines

This paper presents the results of three-dimensional finite element analyses of the suction bucket foundation used for offshore wind turbines. The behavior of the bucket and the response of soil supporting the bucket in dense and medium dense sandy soils subjected to static horizontal load are investigated. Field tests results and a centrifuge model test are used to validate the numerical model. Dimensionless horizontal load-displacement and overturning moment-rotation relationships are derived utilizing the Power law and Buckingham’s theorem. The results show good agreement between the numerical analysis results and the straight lines obtained from the Power law until a specific value of horizontal load and overturning moment. Regarding stress behavior of soil supporting the bucket, due to soil densification and bucket movement, maximum stresses are seen near the bucket tip at the right inside of the bucket. The major part of the applied load is transferred by the bucket skirt. Numerical analysis modeling results show that the bucket rotation and displacement are highly dependent on the bucket geometry and soil properties in addition to loading conditions. Normalized equations and figures for the ultimate horizontal load and overturning-moment capacities are presented and can be used for the preliminary design of the bucket foundations in sandy soils.

Analysis of pullout load capacity of suction caissons in clay by a three-dimensional displacement approach

ABSTRACTA study was made to present analytical solutions of pullout load capacity for a suction caisson subjected to inclined tension in clay. The inclined tension on the skirt of the suction caisson is transformed into an equivalent system comprised of the vertical, horizontal, and moment load applied on the center of the lid. The vertical and horizontal stiffness coefficients along the skirt of the suction caisson in clay are presented by three-dimensional elastic solutions considering the nonhomogeneous and nonlinear property of clay. The vertical, horizontal, and rocking stiffness coefficient of the suction caisson on the base are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of clay. The envelopes of the horizontal and vertical ultimate load capacity for clay are presented. The yield, pullout, and failure for clay are taken into consideration. The effects of load inclination, loading depth, and aspect ratio on the pullout load capacity are shown. Behavior of the suction caisson in clay up to failure is investigated using the relationship between tensile load and displacement and that between depth, vertical, and horizontal pressure.

Evaluation of pullout load capacity of suction caissons in sand using a three-dimensional displacement approach

ABSTRACTAn investigation was conducted to obtain analytical solutions for the pullout behavior of a suction caisson undergoing inclined loads in sand. The inclined load is transformed into an equivalent load system in which the vertical, horizontal, and moment loads are applied on the center of the lid of the suction caisson. The vertical and lateral stiffness coefficients along the skirt of the suction caisson in sands are presented using the new three-dimensional elastic solutions taking into account the nonhomogeneous and nonlinear properties of the sand. The vertical, lateral, and rocking stiffness coefficients on the base of the suction caisson are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of a soil. The yield, pullout, and failure for sands with the nonhomogeneous and nonlinear characteristics are taken into consideration. The effects of the load inclination, the loading depth, and the aspect ratio on the pullout load capacity of the suction caisson are presented. Behaviour of the suction caisson in sand prior to failure is clarified from the relationship between tensile load, displacement, and rotation and that between depth, vertical pressure, and lateral pressure.

Failure mode and capacity of suction caisson under inclined short-term static and one-way cyclic loadings

ABSTRACTIn addition to the loading angle at the pad eye, the types of applied forces will affect the failure mode and the capacity of suction caisson in a soft clay seabed. In this study, a specially designed platform was used to perform model tests with different loading angles and cyclic parameters. First, the short-term static capacities and the failure modes for the typical inclined loading angles were studied, and then the influences of cyclic amplitude, number of cycles and cyclic period on the subsequent failure mode, and caisson capacity were investigated by applying a series of one-way cyclic loadings. The experimental results showed that when the loading angle decreases from 50.2° to 32.0°, the model caisson’s failure mode changes to a combined mode consisting vertical motion, horizontal motion, and anticlockwise rotation, and its corresponding capacity noticeably increases. However, the increases in amplitude, number, and frequency of the previous cyclic loadings would turn this combined failure into a dominant vertical pullout and reduce its capacity to some degree. Therefore, the influence of the previous cyclic loadings should be taken into account to accurately estimate the holding capacity of the suction caisson.

The Pull-out Capacity of Suction Caissons in Model Investigations

Abstract A small-scale model experiment on the pull-out resistance of suction caissons is described. The pull-out force and suction developed within the caisson in the extraction process were recorded during the experiment. A simple breakout model, together with an elementary static formulae, is applied to predict the results obtained experimentally. There is a reasonably good agreement between the experimental results and predictions. An extensive discussion of the approach applied is included. The analysis presented in this paper is original, as it differs from other approaches mentioned in this paper, and leads to acceptable predictions. At the end, the results are also compared with another approach for predicting the capacity of suction caissons.

Embedment Effects on Vertical Bearing Capacity of Offshore Bucket Foundations on Cohesionless Soil

AbstractThis paper presents the results from a series of physical modeling and three-dimensional finite-element (FE) analyses in which the authors examined the uniaxial vertical capacity of suction caissons for offshore wind turbines. The experiments were carried out in quartz sand and involved monotonic application of vertical load. It was found that the drained capacity of suction caissons is dependent on embedment ratio. In contrast, predictions from conventional semiempirical depth factors were found to somewhat underestimate when applied to rough foundations. On the basis of the tests and FE analyses, new expressions for the depth factor of shallow foundations were validated for embedment ratios (aspect ratios) up to unity, calibrating the fitting parameters by using data from a range of soil profiles.

Installation and Monotonic Pullout of a Suction Caisson Anchor in Calcareous Silt

AbstractThis paper reports results from a series of model tests undertaken to provide insight into the behavior of a stiffened caisson anchor during installation and monotonic pullout in lightly overconsolidated calcareous silt. The tests were carried out in a beam centrifuge, varying the installation process (jacked in or jacked in followed by suction-assisted installation), and the consolidation period before anchor pullout. The mudline load inclination was also varied to encompass various mooring configurations. The centrifuge data were used to calibrate analytical installation and vertical pullout capacity models, based on conventional bearing and frictional resistance factors but with strain rate-dependent and strain-softened undrained shear strength for the soil. Piezocone-based direct design approaches were also proposed, deriving end-bearing and frictional resistance from cone tip resistance and sleeve friction, respectively. Holding capacity of suction caisson under inclined loading was presented...

Reliability analysis of suction caissons for moored structures under parameter uncertainties

A study is performed to assess the effect of parameter uncertainties on the uncertainty of the reliability index of suction caissons for moored structures under extreme sea conditions. Uncertain parameters in the statistical model of the maximum dynamic tension of the mooring lines and in the suction caisson capacity model are considered. A first-order approach is used to express the mean and the variance of the reliability index of suction caissons in terms of the mean values of the uncertain parameters, and in terms of the sensitivity vector and the covariance matrix of the uncertain parameters, respectively. The predictive reliability of the suction caisson is estimated as a function of the mean and variance of the reliability index. Suction caissons in normally consolidated clay subjected to loading from catenary and taut-leg mooring lines of an FPSO structure under extreme sea conditions in the Gulf of Mexico are considered for the study. The results show the relative influence of parameter uncertainties on the uncertainty of the suction caisson reliability index.

Numerical Analysis of Inclined Uplift Capacity of Suction Caisson in Sand

Numerical Analysis of Inclined Uplift Capacity of Suction Caisson in Sand

Plastic Flow of Sand and Pullout Capacity of Suction Caissons

A suction caisson has a relatively small length-to-diameter ratio, and the suction-induced seepage forces can liquefy the sand surrounding the caisson, depending on the pullout rate. Houlsby et al. (2005) modeled the seepage forces effect, and its related impact on the effective stresses and the corresponding pullout capacity. However, ignoring potential liquefaction and sand flow that may occur due to the seepage-induced forces can yield an overestimate of pullout capacity as a function of the induced deformation. A Bingham plastic flow model is used to describe the shear stresses as a function of shear strain rate. The general rheological behavior is expressed as when sand flow occurs

Undrained Bearing Capacity of Suction Caissons for Offshore Wind Turbine Foundations by Numerical Limit Analysis

Determining the ultimate capacity of suction caissons in response to combined vertical, horizontal, and moment loading is essential for their design as foundations for offshore wind turbines. However, the method implemented for stability analysis is quite limited. Numerical limit analysis has an advantage over traditional limit equilibrium methods and nonlinear finite element methods in this case because upper and lower bounds can be achieved to ensure that the exact ultimate capacity of the caisson falls within the appropriate range. This article presents theories related to numerical limit analysis. Simulations are conducted for centrifuge model tests, the findings of which reveal the ability of numerical limit analysis to deal with the inclined pullout capacity of suction caissons. Finally, this article proposes an estimation of the ultimate capacity of a 3.5 MW offshore wind turbine foundation on normally consolidated clay based on the typical environmental parameters of Bothkennar, Scotland. Undrained failure envelopes and safety factors are obtained for suction caissons with different embedment ratios. Failure mechanisms, plastic zones, clay stress distributions, and the influence of the skin friction coefficients of caissons are discussed in detail.

Prediction of uplift capacity of suction caisson in clay using extreme learning machine

This study presents the development of predictive models for uplift capacity of suction caisson in clay using an artificial intelligence technique, extreme learning machine (ELM). Other artificial intelligence models like artificial neural network (ANN), support vector machine (SVM), relevance vector machine (RVM) models are also developed to compare the ELM model with above models and available numerical model in terms of different statistical criteria. A ranking system is presented to evaluate present models in identifying the \'best\' model. Sensitivity analyses are made to identify important inputs contributing to the developed models.

A hybrid fuzzy inference model based on RBFNN and artificial bee colony for predicting the uplift capacity of suction caissons

Abstract The suction caisson is an essential part of the foundation system used in offshore platforms. The failure of a single suction caisson may cause the collapse of an entire offshore system. Hence, accurately predicting the uplift capacity of suction caissons is of critical importance to platform function and reliability. This study proposes the intelligent fuzzy radial basis function neural network inference model (IFRIM) to predict the uplift capacity of suction caissons. IFRIM is a hybrid of the radial basis function neural network (RBFNN), fuzzy logic (FL), and artificial bee colony (ABC) algorithm. In the IFRIM, FL deals with imprecise and uncertain information; RBFNN acts as a supervised learning technique to address fuzzy input–output mapping relationships; and ABC searches for the most appropriate parameter settings for RBFNN and FL. Comparison results show IFRIM to be the fittest model for predicting the uplift capacity of suction caissons in terms of accuracy and reliability. A 10-fold cross-validation approach found that the IFRIM reduced the RMSE and MAPE at least 70% and 90%, respectively, below other tested models.