Model Test Analysis Of Influence Of Spudcan Penetration Into Saturated Soft Clay On Adjacent Pile Groups

Drilling ship is an important device in offshore engineering,which is often placed adjacent to a fixed jacket platform in operation.Large soil deformation can be induced during spudcan penetration,leading to adverse effects on the adjacent platform piles.However,limited model test researches have been conducted to investigate the effects of spudcan penetration and extraction adjacent to an adjacent platform pile group.Therefore,small scale model tests both under 1g and 50 g condition were conducted in this study to investigate the effects of spudcan penetration in clay on the group effect of laterally loaded pile groups.A set of 1g model tests were conducted,during which distributions of pile bending moment along pile shaft before and during spudcan penetration were analyzed based on strain gauges instrumented along the shaft.And the distributed pile head loads among group piles were obtained by differentiation of the fitting curves of pile bending moment distributions.Variations of the pile head slope were also recorded to determine the pile head constraint condition.Finally,the effects of spudcan penetration on the group effect of the adjacent pile groups were analyzed based on the modified Poulos method.Conclusions are summarized as follows:(1)In the load stage,distributions of the bending moment are basically the same among group piles,and the pile head load is also uniformly distributed among the piles.With pile head load increasing,the Y multiplier increases and group effect increases as well.(2)The spudcan penetration leads to the change of load borne by near and far pile heads in pile group.Redistribution of the pile head loads among group piles are observed in the tests and the distributed load of the far pile is larger than that of the near pile,leading to larger bending moment along the far pile.Increment of the spudcan-pile clearance leads to larger difference in pile head loads between the group piles.But the trend of redistribution is not influenced,that is,the pile head load of the far pile is still larger than that of the near pile and the maximum bending moment of the far pile remains larger than that of the near pile.(3)Compared with the loading stage,spudcan penetration makes group effect of adjacent horizontally loaded pile groups decrease.The Y multiplier decreases.To further verify the conclusions,the pile shaft strains of the 50 g centrifugal model test were obtained through the single point measurement.The relationship between the bending moment of pile shaft and the penetration depth was obtained.As spudcan penetration depth increases,the pile head load distribution agrees with 1 g model test,accordingly analysing the effect of spudcan penetration on group effect for adjacent laterally loaded pile group.