| When a jack-up drilling platform is inserting piles near the old pile pit,its spudcan foundation may slip into the old pile pit due to eccentric or tilt load,resulting in safety accidents such as pile leg bending and deformation,platform overturning,and even platform collision with the conduit frame.In order to reduce the above engineering risks,this paper carries out a series of spudcan structure type optimization research and comparative analysis,and proposes five new spudcan structure types of rosette-shaped spudcan(four-hole,six-hole,eight-hole),flat-bottomed spudcan,and inward-concave spudcan.The three-dimensional finite element calculation model of the footprint of the jack-up drilling platform spudcan is established by CEL method,and the mechanism of pile-soil interaction,the force characteristics of the spudcan structure and the form of foundation soil flow when inserting piles under different eccentric distance and different pile pit types are analyzed for each new spudcan and traditional spindle-shaped spudcan.Finally,the applicability of the optimized new spudcan structure,test pile pit method and foundation drilling method to the spudcan footprint conditions are compared and analyzed.The specific research contents and related conclusions are as follows:(1)Based on the CEL finite element large deformation numerical analysis method,we have compared and analyzed the mechanism of pile boot-foundation soil interaction,the flow mechanism of the foundation soil,the horizontal range of plastic deformation of the disturbed soil and the difference between the tilt angle of the pile boot and the offset distance of the pile leg and the traditional spindle-shaped pile boot structure,and evaluated the risk of puncture accident when the new pile boot penetrates into the layered foundation of hard clay over soft clay.It is concluded that the horizontal sliding force and pile leg offset distance of the six-hole rosette spudcan are reduced by 32.59% and 60.53%,respectively,compared with the spindle-shaped spudcan,which has the largest adverse effect on the reduction of footprint conditions.Therefore,the new six-hole rosette-shaped spudcan is considered to be the optimal structural form for the footprint condition of the spudcan.(2)Further,a comparative analysis of the load-bearing characteristics of the six-hole rosette-shaped spudcan and the conventional spindle-shaped spudcan is carried out for soft clay and hard clay soils forming two different types of pile pits,inverted conical and cylindrical,respectively.The force characteristics of the spudcan are studied under different shapes,eccentric distances,slope angles and diameters of pile pits.The results show that the six-hole rosette-shaped spudcan has significantly reduced the adverse effects on the footprint under various conditions compared with the traditional spindle-shaped spudcan.The comprehensive analysis shows that the six-hole rosette-shaped spudcan has better piling stability than the traditional spindle-shaped spudcan under the footprint condition.(3)Based on the most unfavorable working conditions of pile insertion stability obtained from the above analysis,a comparative study on the applicability of the six-hole rosette spudcan structure optimization method,the test pile pit method and the foundation drilling method to the spudcan footprint working conditions was conducted.The results show that all the three solutions can effectively reduce the adverse effects after the footprint of the spudcan and improve the stability of the spudcan structure.The evaluation of the effectiveness of the above methods is based on the adverse additional response of the final spudcan penetration: foundation drilling method > new six-hole rosette spudcan > test tread method,but considering the disadvantages of the foundation drilling method and test tread method,such as additional mechanical equipment and construction process,it is considered that the six-hole rosette spudcan structure optimization method is the best way to reduce the adverse effects of the spudcan tread condition. |
