Study On Horizontal Ultimate Bearing Capacity Of Marine Fan Suction Bucket Foundation Considering Scour Effect

Suction drum foundation is widely used in the field of ocean engineering due to its advantages of convenient installation and transportation,no noise pollution in the construction process,high anti-overturning bearing capacity,less steel and recycling and reuse.As the foundation of the offshore fan,besides bearing the vertical load caused by the dead weight of the fan,it is also subjected to the horizontal load of the sea wind,sea wave and sea bottom flow,which puts forward the test of the horizontal bearing capacity of the barrel foundation.In addition,the suction drum foundation has been scoured by water flow during its service,which is easy to cause soil loss around the foundation,affecting the bearing capacity and stability of the suction drum foundation,thus causing the safety problem of the whole fan.Therefore,it is extremely important for the suction drum foundation to ensure its horizontal limit bearing capacity.In this thesis,nonlinear finite element method is used to study the influence of soil loss on suction bucket foundation under complex fan load.On this basis,the influence of soil loss on the horizontal ultimate bearing capacity of suction bucket foundation after scour is analyzed,and the uncertainty of the bearing capacity of suction bucket foundation under the influence of scour is studied as follows:(1)Finite element model was established to study the influence of different soil layers on the horizontal ultimate bearing capacity of suction bucket foundation and the selection of local mesh size.It is found that the horizontal bearing capacity obtained under the action of single sand,single clay and multi-layer soil is quite different,especially in the analysis of sandy soil foundation,which indicates that it is necessary to use multi-layer soil to analyze the horizontal bearing capacity of suction bucket foundation.(2)Based on the allowable value of foundation deformation,the horizontal ultimate bearing capacity of suction bucket foundation under the load of a single fan is studied,and the most unfavorable load is selected.On this basis,the horizontal ultimate bearing capacity of suction bucket foundation under complex fan load is analyzed,and the horizontal ultimate bearing capacity of suction bucket foundation under complex fan load in the scouring process is studied.The research shows that the suction drum foundation has a great influence on the slope of the foundation in the scouring process.At 4m,the slope exceeds the maximum allowable range,which has jeopardized the safety of the offshore fan and may cause the risk of collapse.(3)The established suction bucket foundation in multi-layer soil model is used to analyze the horizontal ultimate bearing capacity of the suction bucket foundation in the case of soil loss in the bucket with inclined slope loss and soil loss in the bucket without inclined slope loss,and the horizontal ultimate bearing capacity of the suction bucket foundation in the case of soil loss outside the bucket with multi-layer floating sand loss and sand soil loss under scouring.The results show that,in the soil loss outside the bucket foundation,the horizontal bearing capacity first remains unchanged,then slowly decreases,and finally rapidly decreases.It can be seen that the soil loss reduces the horizontal ultimate bearing capacity of the suction bucket foundation.(4)Analyze the influence of the uncertainty of parameters such as length-diameter ratio,thickness and range of scouring pit on the horizontal bearing capacity of the suction bucket foundation and the influence of the uncertainty of elastic modulus,friction Angle,cohesion of clay,elastic modulus and friction Angle of sand on the horizontal bearing capacity of the suction bucket foundation.Statistically,the random characteristics of the horizontal ultimate bearing capacity of both conform to the normal distribution.Then,according to the data obtained by Monte Carlo method,the sensitivity of random variables is analyzed by significance analysis method.The results show that the size of scour pit and the friction Angle of sand have significant influence on the horizontal ultimate bearing capacity of suction bucket foundation.