Experimental Study On Oblique Uplift Behavior Of Single Pile

Pile foundation single point mooring is usually used for offshore floating structures.The pile foundation needs to bear the oblique anti-uplift load transferred from the upper floating structure.In the process of wind and wave load,the load of the anti-uplift pile is cyclic with the change of wind and wave.If the oblique uplift bearing capacity of a single pile is insufficient,the local instability of the mooring system will be the least,or the whole mooring system will fail,resulting in irreparable casualties and economic losses.Especially under severe sea conditions such as typhoon and storm surge,the insufficient uplift bearing capacity of pile foundation may cause tilting,drifting and even overturning of Marine floating structure.At present,the research focuses on the vertical pull-out characteristics of pile foundation,but the oblique pull-out characteristics of pile foundation are not fully studied,especially under oblique cyclic load.In addition,the oblique pull-out mechanism and failure mode of pile foundation are not clear.In this paper,a self-designed test device was used to study the oblique uplift characteristics of single pile in saturated Marine clay.The influence of oblique load on the single pile's oblique uplift characteristi cs was analyzed,and the formula of oblique uplift bearing capacity and adhesion coefficient of sin gle pile were deduced.The test results show that the oblique ultimate uplift capacity of single pile in creases with the increase of inclination angle between 0 °and 30 °,while decreases with the increase of inclination angle between 30 °and 90 °.The critical angle is 45 °,that is,when the inclination angle is 0 °? ? ?45 °,the oblique ultimate uplift bearing capacity is determined by the horizontal uplift bearing capacity component,while when the inclination angle is 45 °? ? ?90 °,the oblique ultimate uplift bearing capacity is determined by the vertical uplift bearing capacity component.At the same time,it is found that the vertical displacement range of pile tip is 10%±2.7%of pile diameter when pile foundation reaches the oblique ultimate uplift bearing capacity under different inclination angles.In addition,the failure mode of oblique uplift pile is along the composite shear plane,which shows that there is a void length at the pile top behind the pile and completely separates from the soil around the pile,the residual depth behind the pile is shear failure along the pile-soil interface,and the shear failure in front of the pile is shear failure along the soil around the pile.The cyclic loading test equipment of oblique load was developed,and the experimental study on the influence of cyclic load level,average load level,cyclic load times and dip angle on the oblique uplift behavior of single pile in Marine clay was carried out.Oblique uplift pile under cyclic load can be divided into three states:unstable,stable and metastable.The cyclic load level,average load level,and oblique dip angle all affect the stable state of pile foundation,which may change from stable to metastable,or even from stable to unstable state.In addition,the oblique ultimate uplift capacity of pile foundation aft er cycle is measured by the cyclic stability group test,and the uplift capacity de gradation.It is mainly caused by the loss of pile lateral friction,followed by the dissipation of pile tip suction.The degradation coefficients of oblique uplift bearing capacity corresponding to the four groups of tests with a dip angle of 60 ° and cyclic load characteristics of 0.5-0.2,0.5-0.4,0.5-0.6 and 0.6-0.2 are 0.925,0.832,0.77 and 0.905,respectively.