Study On The Effect Of Scour Depth On The Stability Of Composite Bucket Foundation

Composite bucket foundation is a new type of offshore wind power foundation.It is gradually promoted and applied because it can be prefabricated on land and installed in the sea,which effectively reduce the engineering cost.During the in-situ work,the bucket foundation is subjected to erosion by sea currents for a long time.Field observation showed that there were scour pits around the foundation,which usually located in the back side of the bucket foundation.Therefore,it is necessary to study the impact of scour on the stability of the bucket foundation.In this paper,the horizontal and anti-overturning ultimate bearing capacity of composite bucket foundation under different scour rates was studied by numerical analysis,model test and limit analysis.The main research contents and results are as follows:(1)The effect of scour on the horizontal and anti-overturning bearing capacity of composite bucket foundation was studied.The horizontal and anti-overturning ultimate bearing capacity of composite bucket foundation under different scour rates was calculated by using the method of excavating the soil on one side of the foundation and introducing the concept of soil scour rate.It was found that with the increase of soil scour rate,the horizontal and anti-overturning ultimate bearing capacity of foundation decreased gradually,and the decreasing trend decreased gradually.(2)The effect of scour on H-M envelope of composite bucket foundation was studied.It was found that with the increase of soil scour rate,the H-M envelope of composite bucket foundation had an obvious tendency to shrink inward in the first quadrant,part of the second quadrant and the fourth quadrant.(3)The laboratory small scale model test was carried out.The test results showed that the load-displacement curve of the foundation could be divided into three stages under horizontal or moment loads,which corresponded to the elastic deformation stage,the elastic-plastic transition stage and the plastic stage of soil respectively.When the foundation was rotating under load,the soil behind the bucket was separated from the bucket wall.The horizontal and anti-overturning ultimate bearing capacity of foundation decreased with the increase of soil scour rate.(4)Based on the foundation failure mode of unidirectional loading of composite bucket foundation under different scour rates,the corresponding ground kinematically admissible field was established.The upper limit solution of horizontal and antioverturning ultimate bearing capacity of composite bucket foundation was deduced by limit analysis method.The reduction rate of bearing capacity was calculated,and the relationship between the reduction rate of bearing capacity and soil scour rate was studied,and the results were compared with those of numerical analysis.