Behavior Of Stiffened Bucket Foundation Installation In Soft Clay

With the development of marine resources in China,bucket foundations have been successfully applied to ocean engineering,especially offshore wind power projects in recent years.Stiffeners can be supplied to further enhance the stiffness of structures to avoid bucking during installation.However,stiffeners also induce significant uncertainty for the soil failure mechanism.Therefore,it is a considerable challenge for engineers to accurately estimate the penetration resistance because of the uncertainty of the soil-flow mechanisms inside the bucket and the friction forces on the inside and outside of the skirt surfaces.Thus,it is significant to explore the characteristics of stiffened bucket foundation installing in soft clay,in terms of penetration resistance and soil flow mechanism.The conclusions of this study can provide theoretical basis for the design and construction of practical projects.In this study,model tests and numerical analyses employing large deformation finite element method are carried out to study the penetrating characteristics of stiffened bucket foundation penetrating in soft clay.The influence of scale effect on the penetration characteristics of stiffened bucket foundation was explored,the mechanism of soil characteristics change caused by soil flow was revealed,and the parameter of soil strength after disturbance was established.The research conclusions provide reference for the application of bucket foundation.The main contents and conclusions are as follows:(1)Through 1g model test,it is observed that the soil trapped in the stiffeners gap moves downward with the foundation during the penetration,and an obvious soil-soil shear phenomenon occurs when s/b=4 and 6.7,and the soil flow and disturbance during the penetration of stiffened bucket foundation are greatly affected by the diameter of the foundation D,the spacing of stiffeners s,and the length to diameter ratio L/D.(2)A numerical model is generated and validated with centrifuge testing data in terms of soil flow mechanism and penetrating resistance.The result indicates that the generated numerical model could provide accurate and reliable prediction on the penetration characteristics for stiffened bucket foundation penetrating into clay.(3)The influence of various parameters of the normally consolidated clay on the degree of soil disturbance was analyzed by using parametric study.In order to quantify the degree of soil disturbance,a definition of‘soil movement parameter'is proposed to quantify the soil disturbance.It is found that the strength at mudline,the diameter of the foundation and the width of the stiffener have great influence on the degree of soil disturbance.The formula of soil strength at any position based on soil flow and disturbance is presented.(4)Scale effect is quantified based on parametric study.The normalized soil strength s_u/?'D can be used as a parameter to quantify the size effect with the same foundation shape.Two formulas for engineering analysis and design with considering scale effect are proposed to predict the critical depth of rotational soil flow and the normalized penetration resistance of stiffened caisson penetrating in clay.