Penetration And Horizontal Bearing Behavior Of Skirted Suction Caissons In Saturated Clay

The traditional suction foundation is a large steel thin-walled cylindrical structure with an open bottom and a closed top,which can be used as the foundation for offshore wind power and offshore platforms.The skirted suction caisson adds a "skirted"structure surrounding the traditional suction’s top,which effectively increases the horizontal bearing capacity of the traditional suction foundation and reduces its lateral displacement.Penetrating to a predetermined installation position is a prerequisite for designing the bearing capacity of the suction caisson.In this paper,the effects of different consolidation time and foundation penetration method of clay soil on skirted suction caissons penetration and horizontal monotonic carrying capacity are studied in comparison with traditional suction foundation by model test method,and the process of penetration is analyzed.The influence of horizontal and horizontal loads on the soil around the foundation is obtained through the water injection test of the suction foundation.The study provides theoretical significance for the design and application of skirted suction caissons.The main research results are as follows:(1)Installation mechanism of skirted suction caissons in clay.The friction between the foundation and the soil increase after the skirt structure touches the soil.Suction exhibits a sudden change,which increases approximately linearly and the linear rate of change becomes larger than that before the skirt structure did not touches the soil.For the same consolidation time,the penetration of the skirted suction foundation is greater than that of the traditional suction foundation under self-weight;however,the penetration by suction is reduced,and their amount of soil plug is basically the same.Therefore,the ratio of suction penetration to the length of the foundation hs/L is smaller than that the traditional suction foundation.The ratio hsp/hs of soil plug volume to suction penetration is generally larger than that of traditional suction foundation.(2)Bearing capacity characteristics of skirted suction caissons under horizontal monotonic load.The ultimate horizontal bearing capacity of the skirted suction caissons is significantly improved compared to the traditional suction foundation,with a maximum increase of 45.58%.Under the same load,the horizontal displacement of the skirted suction caissons is less than that of the traditional suction foundation.The traditional suction foundation reaches the limit horizontal bearing capacity.Under this bearing capacity,the corresponding horizontal displacement of the suction foundation is reduced up to a maximum value of 79.43%.At the beginning of loading,the suction rises sharply,and the bearing capacity of the suction foundation is provided by both the internal suction and the interaction between the foundation and the soil.At this time,the movement of the foundation is a combination of rotation and uplift.When the horizontal displacement reaches about 1.5 cm(end of the elastic deformation stage),the suction gradually stabilizes,at the same time,the soil inside the foundation has begun to fail,meaning that the foundation is unstable,and the caisson results in rotation under lateral loading.(3)The influence of skirted suction caissons on the deformation of surrounding soil under horizontal monotonic load.Under the suction,the soil around the foundation is depressed circumferentially.Under the pressure,the soil around the foundation is cracked in a direction perpendicular to the tangent to the foundation.In the early stage of horizontal load application,the uplift area of the soil on the front side of the foundation spreads horizontally and longitudinally around the foundation,and the number and height of soil cracks also increase;in the later period of horizontal load application,the uplift area mainly develops horizontally,and the uplift height and number of cracks increase faster than that in the previous period.Under the limit horizontal load,the soil area in front of the foundation along the loading direction is the active soil pressure area.The soil is swelled by compression and shear,and the shear strength of the soil surface is significantly reduced.The soil exhibits "looseness".The influence range of skirted suction caissons on surrounding soil is larger than that of traditional suction foundation.Due to the existence of skirt structure,soil cracks in the uplift area on the front side of skirted suction caissons are less than that of traditional suction foundation,and the uplift height is lower.After the suction foundation reaches the ultimate horizontal carrying capacity,the foundation is pulled out.About 1/2 of the soil in the traditional suction foundation is pulled out with the foundation under the action of shear.About 90%of the soil in the skirted suction foundation skirt is pulled with the foundation.(4)Pull-up process of water injection based on skirted suction caissons.During the pull-up process by water injection,the soil around the foundation increased.Water injected into the main barrel flowed out of the main barrel,and the foundation could not be completely pulled out.The traditional suction foundation had a larger displacement than the skirted suction caissons.The time when the pressure in the bucket reaches the peak will affect the time of the pull-up displacement.The basis of the pressure in the bucket first reaches the maximum pull-up displacement.The water injection rate in the early stage affects the pressure change in the bucket.The water injection rate is fast and the pressure in the bucket rises rapidly.At the same time,the soil cracks in the bucket will increase.In the later water injection process,the pressure in the bucket will dissipate quickly;the water injection rate is slow.It has little effect on the soil in the bucket,and the pressure in the bucket dissipates slowly during the later water injection process.According to the balance formula of the force,the resistance during the pull-out of the suction foundation is calculated.It is found through comparison that when the internal pressure of the suction foundation reaches the maximum value,the pull-out resistance of the suction foundation is the largest at this time.